All About Space Annual Vol. 3 2016

NEW

Galactic evolution

Discover Pluto's moons

Measuring galaxies

Mapping our Solar System

Colonising space

The future of space travel Amazing NASA projects

Exploring deep space

Investigating Mars

EXPLORATION | SOLAR SYSTEM | DEEP SPACE | SPACE SCIENCE | FUTURE TECH

Welcome to the

This year, astronomers were able to capture breathtaking images of the eclipse of a super moon. The next lunar eclipse visible from the UK won’t occur until 2019 and a lunar eclipse coinciding with a super moon won’t occur again until 2033. Fortunately, beyond that, there are so many more incredible events occurring in space. In the All About Space Annual 2016 we take a look at the intrepid missions to the planets of our Solar System and our cosmic backyard. We journey beyond our home Solar System and even the Milky Way, observing the biggest galaxy in the universe and Earth’s supernova neighbour. We dive into the depths of supermassive black holes and answer the mind-bending questions you’ve never thought to ask: what if the Moon exploded? What if Earth stopped spinning? Then we look to the future to see what incredible projects NASA is working on and theorise how the human race might go on colonise space. This book is crammed with fascinating facts, stunning illustrations and interviews with some of the world’s top scientists, so continue to explore space and its far-flung celestial bodies now!

Imagine Publishing Ltd Richmond House 33 Richmond Hill Bournemouth Dorset BH2 6EZ ☎ +44 (0) 1202 586200 Website: www.imagine-publishing.co.uk Twitter: @Books_Imagine Facebook: www.facebook.com/ImagineBookazines

Publishing Director Aaron Asadi Head of Design Ross Andrews Production Editor Hannah Westlake Senior Art Editor Greg Whitaker Designer John Ndojelana Photographer James Sheppard Cover images courtesy of NASA, Adrian Mann, Jay Wong, Reaction Engines, DSI, Science Photo Library & Wiki Commons Printed by William Gibbons, 26 Planetary Road, Willenhall, West Midlands, WV13 3XT Distributed in the UK, Eire & the Rest of the World by: Marketforce, 5 Churchill Place, Canary Wharf, London, E14 5HU Tel 0203 787 9060 www.marketforce.co.uk Distributed in Australia by: Network Services (a division of Bauer Media Group), Level 21 Civic Tower, 66-68 Goulburn Street, Sydney, New South Wales 2000, Australia Tel +61 2 8667 528 Disclaimer The publisher cannot accept responsibility for any unsolicited material lost or damaged in the post. All text and layout is the copyright of Imagine Publishing Ltd. Nothing in this bookazine may be reproduced in whole or part without the written permission of the publisher. All copyrights are recognised and used specifically for the purpose of criticism and review. Although the bookazine has endeavoured to ensure all information is correct at time of print, prices and availability may change. This bookazine is fully independent and not affiliated in any way with the companies mentioned herein. All About Space Annual Volume 3 © 2015 Imagine Publishing Ltd ISBN 9781785461637

Part of the

bookazine series

Contents 100 wonders of space pg.8

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Exploration

Solar System

24 10 daring space missions

60 Birth of the Solar System

34 Mapping the Milky Way

70 This is Pluto

42 The search for New Earth

78 Exploring Mars

50 Interstellar space travel

82 Traversing Callisto 86 Space volcanoes

Deep Space

Space Science

96 The power of supermassive black holes

130 What if the Moon exploded?

104 The biggest galaxy in space

140 A beginner's guide to space time

113 Earth's supernova neighbour

148 Do we live in a multiverse?

Future Tech 166 20 incredible NASA projects 176 Space colonies 182 Asteroid nets 184 10 out of this world rovers

150 What is the shape of space? 152 How to build a galaxy 160 How does our galaxy measure up?

“Roving vehicles have been sent to the Moon and Mars since the 1970s” ©NASA, Mark A. Garlick

120 The Shapley supercluster

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1 Saturn’s Rings

100 wonders

The rings of Saturn are extraordinary. First observed by Galileo Galilei in 1610, these structures are incredibly thin, measuring just one kilometre (0.62 miles) from top to bottom. They’re made up of billions of particles of ice and rock, some as large as mountains and others too small to be seen with the naked eye. It’s not known for sure how old the rings are, or exactly how they formed, but it is thought possible that the fragments are pieces of shattered moons, smashed to bits by collisions in the not too distant past.

of space From giant craters to supermassive black holes and alien planets: explore All About Space’s favourite parts of the cosmos

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100 wonders of space

6 Life As far as we know, Earth is the only planet to harbour living organisms, but chances are there are many more planets out there like our own.

2 Andromeda

7 Great Red Spot

Currently sitting at just over 2 million light years from Earth, our closest spiral galaxy Andromeda, and its 100 million stars, are rapidly getting closer. They are rushing towards us at a speed of 402,000 kilometres (250,000 miles) per hour, on a course for collision 4 billion years from now.

The width of two Earths, Jupiter’s Red Spot is by far the biggest storm in the Solar System, and is given its red colour by the effects of UV light on the clouds.

3 The Moon

SPRINGS: New Moon

Earth

SPRINGS: Full Moon

Earth

NEAPS: First Quarter

The Moon is a space wonder right on our own doorstep. As it orbits the Earth, its gravity tugs on the oceans, creating a measurable bulge; as the oceans swell, we see the effects on the ground as tides. The Sun has a similar, but smaller, effect, and when the Moon and the Sun are in line, the pull on the oceans adds together, creating extra high ‘spring tides’ once a fortnight.

These iconic columns of gas and dust were first imaged by the Hubble Space Telescope in 1995, and in 2015 the pictures were retaken in high definition. Lit by ultraviolet radiation released by massive, young stars in the Eagle Nebula, the pillars are constantly being shaped, heated and eroded, and hidden inside are the infrared traces of brand-new stars.

These meteors shower the atmosphere every November as we pass through a trail of dust and gas left by comet Tempel-Tuttle as it nears the Sun.

9 Methane seas Weather is not exclusive to water worlds like our own; Saturn’s moon Titan has seas, clouds and rain of liquid methane.

10 Giant moon cliff

The tallest cliff in the Solar System is on Uranus’s moon, Miranda. Verona Rupes is 20 kilometres (12 miles) deep, and it would take 12 minutes to fall from top to bottom.

Sun

Sun

Earth Sun

NEAPS: Last Quarter

4 The Pillars of Creation

8 Leonids meteor shower 

5 Sombrero Galaxy Named for its hat-like appearance, the Sombrero is a galaxy within a galaxy. The flat disc, viewed almost side-on from the Earth is the most obvious feature, resembling the wide brim of a hat, but if you look again in the infrared spectrum a much larger elliptical galaxy becomes visible, completely encasing the central disc.

11 Acid atmosphere The atmosphere of Venus is 96 per cent carbon dioxide, and the pressure at the surface is 90 times that on Earth. It has little water, and the clouds are made from corrosive sulphuric acid.

12 Accretion disc Black holes are surrounded by a spiralling disc of gravitationally trapped matter. It keeps swirling until something disturbs the disc and it tumbles into the void.

13 Vesta's giant mountain Earth

Sun

Rheasilva peak at the centre of the Rheasilvia crater on the asteroid Vesta is 22 kilometres (13 miles) high, rivalling Mars’s Olympus Mons volcano as the tallest peak in the Solar System.

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100 wonders of space

14 Valles Marineris

Valles Marineris is Mars’s answer to the Grand Canyon, but on a grander scale. It extends for 3,000 kilometres (1,800 miles), and cuts an eightkilometre (five-mile) deep scar into the planet’s surface. Measuring 600 kilometres (370 miles) across, this canyon is thought to have formed 3.5 billion years ago.

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15 Hellas Planitia

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Hellas Planitia is an ancient impact crater measuring over 2,000 kilometres (1,200 miles) in diameter, and extending down for four kilometres (2.5 miles). This enormous scar on the southern hemisphere is the largest complete crater on the surface of Mars, created by an asteroid impact around 4 billion years ago.

16 Olympus Mons

This imposing mountain is the tallest volcano in the Solar System; standing at an incredible 25 kilometres (16 miles) tall. It easily eclipses the tallest volcano on Earth, Mauna Loa. On Mars, the surface is static, so lava continues to erupt in one position, generating a volcano of truly gargantuan proportions.

17 Faces on Mars

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17

When Viking 1 made its mission to Mars in the Seventies it was greeted by a strangely familiar sight; two faces were staring back from the bare rocks on the surface. Unfortunately, high-resolution images of these features revealed both to be natural landforms, and not sculptures created by intelligent life.

18 Utopia Planitia

The crater of this Martian impact basin contains landforms known as ‘thermokarst’, with geometrically shaped lines and depressions with scalloped edges. When Viking 2 arrived in 1979, it found a thin layer of ice on the surface, and the lines in the ground are thought to have been formed by wedges of subsurface ice.

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19 Mars haboobs

Mars is coated in a layer of fine magnetic dust, and experiences some incredibly violent weather; warm air in the deep Hellas Basin can generate storms that engulf the entire planet.

100 wonders of space

24 Dark nebulae These clouds are so dense that no light can pass through; it is all absorbed, making it appear as though there are gaps in space.

25 Shooting stars

20 Red Square Nebula 21 The diamond ring The unusual geometric shape of this nebula found in the constellation of Serpens remains an astronomical mystery, but the leading hypothesis is that we are looking at the side of several cones of gas released by the star or stars sitting at the centre. The cones are at right angles to one another, producing the shape of a square, but if we looked from a different angle we would be able to see directly into one of the cones, and it would appear as a red ring.

At first glance, this photograph captured by the European Southern Observatory’s Very Large Telescope might look like a single object in the form of a cosmic diamond ring, but in reality, it is the result of an interaction between two objects. The ring itself is formed by the blue bubble of a planetary nebula known as Abell 33, created when the atmosphere of a dying Sun-sized star ballooned into space, and the ‘diamond’ is a well-positioned bright foreground star.

22 Callisto ice spires

Jupiter’s moon Callisto was thought to be a dead object, an ancient cratered world coated in a layer of ice, but images captured by NASA’s Galileo spacecraft in 2001 revealed spires jutting out from the

These wonders of the night sky have long fascinated humanity. They happen when chunks of dust and rock burn up as they pass through the atmosphere.

26 Stellar magnets Magnetars are neutron stars with extreme magnetic fields. They are rare and unpredictable, suddenly erupting with gamma-ray bursts before going quiet.

27 Titan

surface. The icy spikes are coated in dark dust which absorbs heat from the Sun, causing the ice to melt, and gradually eroding the surface.

Saturn’s moon Titan is unique in the Solar System; it is the only satellite with its own atmosphere, and is covered in seas of liquid ethane and methane.

28 Teatemperature star The nearby brown dwarf star, CFBDSIR 1458+10B, is part of a binary system and has a surface temperature comparable to a freshly made cup of tea.

29 Hypervelocity stars

The surface of Callisto is coated in spiky mounds of ice, surrounded by dark puddles of dust

23 Subsurface oceans Beneath the surface of seemingly frozen moons there are potentially vast quantities of liquid water. In the far reaches of the Solar System the temperature plummets, but friction caused by the gravitational interactions between a moon and its parent planet could melt subsurface ice, resulting in hidden oceans. The tidal motion of these oceans as the moon orbits would help to keep the water in liquid form. The best candidates for subsurface water in the Solar System are Jupiter’s moons Europa, Callisto and Ganymede, and Saturn’s moons Mimas and Enceladus.

Warm convecting ice

Europa has a magnetic field, indicating that something is conducting electricity below its surface; one explanation is partially melted icy slush.

Liquid ocean under ice

Europa is still warm at its core, so it is thought more likely that the water inside is truly in liquid form, making up a salty subsurface ocean.

Some stars travel at speeds over 3.2 million kilometres (2 million miles) per hour, fast enough to escape the gravitational pull of their parent galaxy.

30 Himiko

Also known as the Lyman-alpha blob, Himiko is an enormous ancient galaxy; it is so far away that we are looking 800 million years into the past.

31 Hamburger Galaxy

Positioned edge-on to Earth, this spiral galaxy appears to us like a flat red-orange disc of stars and dark dust, reminiscent in shape of a popular American food.

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Molten iron core

100 wonders of space

Like Earth, the core of a diamond planet is thought to be composed of molten iron, or a combination of iron and carbon (molten steel).

Silicon-based materials Around the core is a second molten layer containing siliconbased materials, such as silicon carbide (SiC) or enstatite (MgSiO3).

33 Massive water reservoir

The quasar APM 08279+5255 hides a black hole 20 billion times the Sun's mass, and contains an ancient water cloud. The gas surrounding the black hole contains 140 trillion times more water than Earth’s oceans.

34 Gammaray bursts Surface graphite

The lower pressures at the surface would result in a layer of graphite, and depending on the atmosphere and temperature, there could also be hydrocarbon weather.

Diamond layer

32 Diamond planets

Our own Solar System is dominated by oxygen and the terrestrial planets inside it are made from silicon-based rocks. But elsewhere in the universe it is a different story; in carbon-dominated systems, some planets are thought to be made from diamond. One of the first candidates for

If there is enough pressure beneath the surface, a rigid band of crystals could form, creating a thick layer of diamond.

Once a day, a random point in the sky blazes with an intense pop of energy known as a gamma-ray burst. Each burst is thought to be the final firework display of a massive star as it collapses down to form a black hole.

a diamond planet is a super-Earth known as 55 Cancri E. It is 40,000 light years away, twice the size of Earth and almost eight times the mass, and beneath a surface of graphite, planetary scientists think it could contain a thick shell of precious stones and other crystal structures.

35 Cosmic Microwave Background The cosmic microwave background (CMB) is evidence of the Big Bang written all over the fabric of the universe. It was discovered by Bell Telephone Laboratories in the Sixties, and was originally little more than a nuisance, interfering with radio communications, but it soon became clear that this background radiation was special. The CMB represents

Very early universe

In the earliest stages of the universe, it was so hot and dense that free electrons scattered photons, and no light could escape.

the oldest light in the universe; the thermal radiation left over from the Big Bang. The early universe was hot and dense but over the last 13.7 billion years, it has stretched and cooled. As the universe has expanded, the heat signature expanded with it, leaving behind a visible fingerprint in the form of a uniform layer of microwave radiation spread across the sky.

Creation of the CMB

The first light of the universe was released 380,000 years after the Big Bang, when the universe had cooled to around 2,700°C (5,000°F).

Expansion

As the universe has continued to expand, the first light has expanded with it, and the thermal signature is now just 2.725 degrees above absolute zero; visible as microwaves.

36 The Cold Spot The Cosmic Microwave Background (CMB) (see wonder number 35), is the afterglow of the Big Bang, and is relatively uniform across the entire sky, however there is a strange cold spot in the lower right-hand corner. The chance of this happening at random is around 1 in 100, and its presence is puzzling cosmologists. Possible explanations put forward include an enormous supervoid, a defect known as ‘texture’, and even the presence of a parallel universe.

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100 wonders of space

Gas and dust

The material surrounding the black hole forms a doughnut shape as it swirls towards the centre. It has a corresponding magnetic field, and clouds of charged particles form above and below.

Black hole

The supermassive black hole at the centre is the powerhouse of the quasar, distorting space-time with its enormous gravitational pull and drawing in the surrounding dust and gas.

Jets

The magnetic field that surrounds the black hole channels radiation away in two vast energetic jets, visible as a quasar or a blazar depending on the viewing angle.

38 Hubble Deep Field

37 Quasars Quasars, or ‘quasi-stellar radio sources’, are some of the brightest and most energetic objects in the universe; they can release thousands of times as much energy as the Milky Way. A quasar is a supermassive black hole engaged in a feeding frenzy. As the black hole at the centre of a large galaxy draws in material, it swirls around in a vast disc and the particles rub against one another, releasing huge amounts of energy as they are torn apart. As they twist towards the event horizon, magnetic field lines funnel enormous quantities of radiation outwards in two huge jets, creating a dramatic beacon visible from the Earth.

39 Stephan’s Quintet

One of the most astonishing things about space is what appears when you point a telescope at nothing. Between 2003 and 2004, the Hubble Space Telescope was aimed at an empty portion of the sky in the constellation of Fornax and in the eight years that followed, it kept returning, creating an even more detailed image of what appeared to be a blank patch of sky. The resulting images revealed a sea of galaxies, stretching back in space and time 13.2 billion light years, almost to the birth of the universe.

This cluster of five galaxies was discovered in the 19th century and demonstrates the effects gravity on a monumental scale. Three of the galaxies are so close that immense gravitational tides have made visible changes to their structure, pulling on their spiral arms and distorting their shapes as they twist towards an inevitable collision. The bluer galaxy at the bottom left of the image is an interloper, 240,000 light years away from the others, it is not actually part of the group.

40 Dark energy We know little about dark energy other than that it is accelerating the expansion of that which followed the Big Bang. It is thought to make up between 68 and 71 per cent of the universe.

41 Dark matter Between 24 and 27 per cent of the universe is thought to be composed of dark matter, made up of subatomic particles that interact only weakly with ‘ordinary’ matter.

42 Rare types of matter

‘Normal’ atomic matter, made up of protons and neutrons makes up just five per cent of the universe. The remainder is dark matter and dark energy, neither of which have ever been directly detected.

43 Red dwarfs

These small, dim stars burn so slowly that they are thought have lifespans longer than the total age of the universe, meaning that none are yet old enough to have died.

44 Asteroid belt Between Mars and Jupiter lies a band of leftovers from the beginnings of the Solar System; either the remnants of a planet that failed to form, or the fragments of a broken one.

45 Oort cloud The Solar System is encased in a sphere of icy objects, collectively known as the Oort cloud. The Sun’s gravity at that distance is so weak that passing objects can send comets hurtling inwards.

Old elliptical galaxies

46 Backwards spiral galaxy Spiral galaxies Distant new galaxies

The arms of spiral galaxies trail backwards as they turn, but NGC 4622 is turning in the same direction that its arms point, possibly as the result of a collision that upset its spin.

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100 wonders of space

47 Pulsars

When pulsars were discovered in 1967, Jocelyn Bell thought she might have intercepted communications from an alien civilisation. While searching for the high-energy twinkling of quasars, she noticed a patch of sky emitting regular pulses of radio waves every 1.3 seconds. The signal was actually generated by a neutron star. Neutron stars are created when a star between eight and 25 times the mass of the Sun runs out of fuel and collapses. As the neutron star spins its radio jets spin too, sweeping across the sky in regular pulses.

48 Hoag’s Object This unusual object is a ring galaxy, one of the rarest galaxy types in the universe. At the centre is a spherical bulge of old orange-red stars, and around the edges is a ring of bright blue hot young stars. Other ring galaxies are thought to have formed following a collision, or due to a rapidly spinning central bar, but the origin of Hoag’s Object is unknown. If you look inside, another ring galaxy is visible far in the distance.

Sun

50 Massive star VY Canis Majoris is one of the largest stars in our galaxy; 2,000 times the size of the Sun, and between 30 and 40 times the mass. Within just a few tens of millions of years, VY Canis Majoris will collapse, creating a supernova that will spray the surrounding space with water, silicone compounds and carbon, giving rise to a new generation of smaller more Sunlike stars.

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49 Spirograph Nebula The star at the centre of these geometric swirls used to be like our own Sun, but a few thousand years ago it started running out of fuel and ballooned to become a red dwarf. Since then, its fuel has disappeared, and its envelope has begun expanding. The white dwarf now forming at the centre is unpredictable, and scientists believe that its erratic winds could be making these strange patterns in its nebula.

100 wonders of space

51 Exoplanets

Hot Jupiter HD 189733b

These enormous gas giants orbit close to their parent stars, blocking the light as they pass and making their presence easy to detect. Some, like HD 189733b, orbit closer than Mercury.

Until 1994, the planets of the Solar System were the only planets that we were aware of in the universe. It was always thought likely that other stars had companions. The first exoplanet was found orbiting a pulsar and, just a year later, in 1995, another was discovered orbiting a Sun-like star. NASA’s JPL lists a total of 5,003 known exoplanets.

Hot Neptune Gliese 436 b

These Neptune-sized planets orbit close to their parent stars, and a year on the surface passes quickly, making them easy to detect from far away.

Chthonian planet Osiris (HD 209458b) Gas giants orbiting close to their stars are bombarded by radiation and solar winds, and evaporate rapidly. Chthonian planets are the hypothetical rocky remnants that will be left behind.

Super-Earth HIP 116454b

These planets have a mass greater than Earth, but lower than Neptune. Despite the name, not all super-Earths are Earth-like – some are blisteringly hot, others are frozen, and some are made of gas.

Water world Kepler 22b

This group of ocean planets are composed mostly of water. Some are thought to have thick atmospheres, supporting liquid water on the surface, but others are hot, steamy and unstable.

Terrestrial 55 Cancri e

These are the planets that, like Earth, are composed mainly of rocks or metals. It is thought that there could be as many as 40 billion habitable terrestrial planets in the Milky Way alone.

Rogue planet WISE 0855-0714

Rogue planets do not orbit their parent star. Instead, they orbit the centre of their galaxy directly, still warmed by their molten cores, but often encased in ice.

Gas giant GJ 540b

These enormous planets, just like Jupiter and Saturn, are several times the mass of Earth, and are composed mostly of gas, with a molten rocky or metallic core.

Brown dwarf Teide 1

These objects are larger than planets, but smaller than stars. With a mass in between, they were unable to sustain a nuclear fusion reactor that makes a star, and are sometimes known as ‘failed stars’.

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100 wonders of space

57 Supernovae When massive stars die they go out with a bang, releasing as much energy as the Sun will during its entire lifetime in just fractions of a second.

58 South PoleAitken Basin

52 Horsehead Nebula This remarkable pillar of dense dust and gas is named after the horse-like head and neck at its tip. It is part of a larger optical nebula known as Barnard 33, and is visible in pink silhouette thanks to an extremely bright five-star system, Sigma Orionis – part of the constellation of Orion. The Horsehead pokes out of a larger cloud system, and inside its dark interior new low-mass stars are being born.

The south pole of the Moon has a spectacular impact crater, covering an area measuring around 2,600 kilometres (1,600 miles), and deeper than the height of Mount Everest.

53 Einstein Cross

One of Albert Einstein’s greatest ideas was that the universe is made from a fabric called space-time, and that mass causes this fabric to bend, like balls sitting on a trampoline. Incredibly, there is evidence of it happening right before our eyes. The Einstein Cross is a single quasar, but it looks like four because a galaxy sitting in front of it bends space-time, curving the light as it passes, and acting like a lens to duplicate the image.

59 Chelyabinsk meteorite This 19-metre (62-foot) wide asteroid exploded in mid-air over Russia in 2013; an event that happens on this scale approximately once every 30 years.

60 Cataclysmic variable stars In some binary systems, a white dwarf and a larger star, like a red giant, orbit close to one another. The white dwarf feeds on its companion, creating an accretion disc that glows.

54 Caloris Basin This enormous impact basin measures 1,500 kilometres (930 miles) in diameter, and is one of the hottest places on Mercury. Its perimeter is studded by volcanic vents, visible here as bright orange hot spots, and its interior is pockmarked by hundreds of more recent impacts.

61 Total solar eclipse These rare events are only possible thanks to the chance position of the Moon; at its current distance, the Moon appears the perfect size in the sky to completely cover the Sun’s disc as they line up. Read more about them in our feature on page 64.

55 Mercury double sunsets

When Mercury is at its closest point to the Sun, it travels so quickly that its rotational speed can’t keep up, and after the Sun sets it reappears and sets again.

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56 Aurorae

The aurora borealis and the aurora australis are some of nature’s most spectacular wonders. The Sun releases a stream of charged particles called the solar wind, and this feeds into the magnetosphere around our planet, dislodging other particles and slamming into the gases that make up the atmosphere. These collisions excite the gas molecules, and make them glow. Depending on the height and the type of gas hit different colours are made.

Outer crust

The outer layer of a neutron star is rigid and incredibly smooth; the tallest ‘mountain’ on the surface measures just fractions of a centimetre.

Inner crust

The matter inside a neutron star has degenerated, and exists as neutron dense nuclei, alongside free superfluid neutrons and electrons.

62 Neutrons

100 wonders of space

Neutrons are subatomic particles of neutral charge, and in normal matter they make up part of the atomic nucleus, sitting alongside positively charged protons. Under the immense pressure inside a neutron star however, atoms degenerate and positively charged protons and negatively charged electrons are crammed together so tightly that they too start to form neutrons, making up the bulk of all the matter contained inside.

64 Ant nebula

This object bears a striking resemblance to the head and thorax of an ant, but look closely and a dying star is visible at its core; between the two segments, a star not unlike our Sun is in the midst of collapse. The shape of its explosion has puzzled astronomers, and rather than being uniform in all directions, the gas is wound up into two symmetrical lobes. It is thought that there may be another star, stirring the gas with its gravitational pull, or that the spin of the dying star could be creating these enormous swirls.

Outer core

The matter at the base of the crust is crushed into strange patterns of sheets, rods and spirals, known as ‘nuclear pasta’.

63 Neutron stars When a massive star runs out of fuel, the outwards explosive force that opposes the inwards crunch of gravity is removed, and in just fractions of a second, the structure collapses. Very large stars collapse entirely to form black holes, but smaller

Inner core

What lies within the core of a neutron star is unknown, but it could contain exotic particles like unbound quarks.

stars still retain a shred of their former presence in the shape of a neutron star. They are the size of a city, but contain the mass of around 500,000 Earths, and are so dense that a single teaspoonful of their matter would weigh ten million tons.

66 Orion Nebula The astonishing colours of the Orion Nebula have made it one of the most famous sights in the sky. Just 1,500 light years from the Earth, the glowing red cloud of ionised hydrogen is dominated by a group of three enormous stars collectively known

65 Twin stars

Around 85 per cent of the stars in the Milky Way are thought to move in pairs, threes, or in larger groups. They are known as binary or multiple star systems, and instead of existing alone, the companions orbit around a common centre of mass. Some pairs can easily be seen through a telescope, while others look like one bright star, but can be distinguished by fluctuations in the colour of their light as they orbit, and some pass in front of one another, producing measurable eclipses that can be seen from Earth.

as the Trapezium. The nebula is just 30,000 years old, and is a place of intense star birth. The hot young Trapezium stars have blown a hollow in their dust shroud, and are illuminating the surrounding cloud.

67 Crab Nebula

This five light year-wide nebula is the remnants of a supernova explosion that lit up the southern sky in 1054 CE. The gas cloud is expanding at a rate of around 1,800 kilometres per second (1,100 miles per second), and the gas creates a glowing rainbow. In the interior, the blue and green filaments are oxygen and sulphur, and towards the edges, the orange and red are hydrogen and oxygen. At the very centre, electrons glow blue as they circle the magnetic field of a neutron star.

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100 wonders of space

72 Globular clusters

These dense symmetrical spheres contain ancient red-orange stars, and are the oldest subsystems inside galaxies, thought to have formed between 13 and 15 billion years ago.

73 Reflection nebula

These nebulae do not emit any light of their own, but they reflect light from nearby stars, revealing their dusty outlines.

68 Whirlpool Galaxy

74 Asteroid moons 

This near-perfect swirl is a classic example of a spiral galaxy. Like our own galaxy, bright blue stars are formed within the enormous arms, twisting around a central bulge of older orange-red stars in the last phases of their existence. The spirals are lined with dust lanes composed of dark silicon and carbon, and clouds of hydrogen gas glow red as they are excited by the light from the young stars.

It is not just planets that have satellites, around 16 per cent of large near-Earth asteroids have one, or even two, moons of their own.

75 Cosmic voids The structure of the universe looks something like a threedimensional web, with most of the galaxies arranged into clumps and filaments. In between, there are vast holes.

76 Wolf-Rayet stars These hot, massive stars are nearing the end of their lives, and have started losing their atmosphere at an astonishing rate as solar winds blow their gases out into space.

77 Ceres Ceres is the largest object in the asteroid belt; its growth was stunted by the gravity of Jupiter, and at only 950 kilometres (590 miles) across, it is known as an embryonic planet.

78 Large quasar group

The largest structure in the known universe is a cluster of quasars, the violent nuclei of early galaxies, stretching in a chain that covers 4 billion light years.

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69 Space volcanoes

70 Io

The Solar System is full of volcanic activity. The largest volcano of all, Olympus Mons, is located on Mars, and Venus boasts the highest number of volcanoes of any planet, with over 1,600 major volcanic features, and tens of thousands of smaller volcanoes. Though neither planet has seen recent volcanic activity, it is possible that some are still active. Volcanoes are not just restricted to planets; Jupiter’s moon Io is more volcanically active than Earth, and Neptune’s moon Triton and Saturn’s moon Enceladus both harbour cryovolcanoes, which spew not lava but water. The gravitational pull of the parent planet of each moon warps their shape, causing their internal structure to melt and flex, and resulting in violent eruptions.

71 Light 'echoes' In early 2002, the star V838 Monocerotis suddenly became incredibly bright, and then rapidly dimmed again in an unprecedented display that stumped astronomers. During the event, which is known as a ‘light echo’, the star grew hugely in diameter, but

unlike other ageing stars, it did not lose its outer layers and instead they cooled until its surface was almost cold enough to touch. The light emitted was reflected by dust that the star had already expelled, revealing layers of previously invisible swirls.

Jupiter’s third largest moon, Io, is the most volcanically active place in the Solar System, capable of jettisoning lava 300 kilometres (190 miles) into the sky. Its atmosphere is thin and sulphurous, and its surface is constantly being smoothed and remodelled by lava flows. Incredibly, Io acts as a lightning rod, and as it dips through Jupiter’s magnetic field it generates currents of up to 3 million amperes, which zip down towards the surface of the gas giant below.

100 wonders of space 1996

2006

1997

2005

79 Solar Flares

The sudden release of magnetic energy from the Sun’s atmosphere sends out bursts of radiation, releasing 10 million times more energy than an erupting volcano.

1998

2004

1999

2003

2000

2002 2001

80 Solar Maximum The Sun is a consistent presence in Earth’s sky, but it isn’t quite as constant as it might appear. Its magnetic flux varies on an approximately 11-year cycle, and at its peak, known as the solar maximum, sunspots are visible on its surface almost

1948

Key

Halley's Comet Planet

of these spots rises, appearing in two bands one either side of the equator, and these active regions are often associated with solar flares and coronal mass ejections, which start to ramp up as the solar maximum passes.

continuously. In areas where the Sun’s magnetic field is at its strongest, the temperature plummets; this creates visible dark spots, some of which can measure 50,000 kilometres (31,000 miles) across. During the solar maximum, the number

tune 1961 Nep 1977

us Uran

1926 1921

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1915

81 Halley’s Comet

It might only measure a few kilometres in diameter, but Halley’s Comet is the most famous object of its kind in the Solar System; records of the chunk of ice date back to 240 BCE, and it was present during the Battle of Hastings in 1066. It is in orbit around the Sun, and returns to pass by Earth approximately every 79 years, making its most recent appearance in 1986 and is expected to return in 2061.

1983

iter Jup

1985

s Mar 1986 Earth Venus Mercury

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100 wonders of space

87 Micro black holes These hypothetical black holes are thought to have formed early in the history of the universe, and contain the mass of a mountain crammed into the volume of just one atom.

88 Neutrinos These subatomic particles are made in violent explosions, but with no mass and no charge they can travel through objects, reaching Earth and pointing us back to their source.

82 Cigar Galaxy

This edge-on spiral is known as a starburst galaxy, and is a hive of star formation activity. The new stars are fuelled by supernovae, and several have been observed over the last few decades. The most recent in the area occurred in 2014.

83 Heart Nebula

A favourite space object on Valentine’s Day, IC 1805 bears more than a passing resemblance to a heart. The clouds of dust and gas have been shaped by a cluster of newly formed stars known as Melotte 15, only 1.5 million years old.

89 Hot ice planets  The temperatures on the planet GJ 436b are well above the boiling point of water, but the pressure is so high that it has turned to an exotic form of ice.

90 Dune fields Despite their differences, Earth, Venus, Mars and Titan all share a common feature; wind in the atmosphere of each has swept the surface dust into rippling dunes.

91 The hole in space We’re located inside a hole in the interstellar medium known as the Local Bubble, formed by a group of exploding supernovae around 10 million years ago.

92 Pole stars Polaris is the current North Star and is almost lined up with magnetic north, but the Earth’s axis spins in a cone-shape every 26,000 years, so this won’t always be the case.

93 Rum cloud Sagittarius 2b, a cloud near the centre of the Milky Way, has 10 billion, billion, billion litres of alcohol, along with a molecule called ethyl formate, which smells like rum.

94 Dinosaur crater

Chicxulub is a 66-million-year-old impact crater in Yucatan, Mexico. It is the site of the asteroid impact that let to the mass extinction event that killed the dinosaurs.

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84 Colliding galaxies The Antennae Galaxies are in the midst of a violent merger. The two galaxies are entwined involved a chaotic dance that began a few hundred million years ago; their dim orange cores are still visible and distinct, but their arms are wrapped together, and bright blue newly formed stars are bursting out of the chaos, lighting up the hydrogen gas in pink.

85 Tarantula Nebula 86 Cartwheel Galaxy The wispy arms of the Tarantula Nebula are made from partially ionised hydrogen gas, excited by a supercluster of massive stars called R136. It is the largest star-forming region in nearby space: hidden within it are more than 800,000 new stars. Their energetic activity blows holes in the clouds surrounding them, giving the nebula its lace-like structure.

This spiral galaxy suffered a head-on collision that created rings of star formation that rippled out from the centre. Ultraviolet and X-ray light released by new stars and violent black holes are visible in this image as purple and blue, while the green visible light shows the spokes of the cartwheel, revealing clues about the galaxy’s shape before the impact.

100 wonders xxxxxxxxxxxxx of space

95 Huge canyon

96 Giant river bed

Saturn’s moon Tethys is scarred by a 2,000-kilometre (1,200-mile) long canyon called Ithaca Chasma that runs three quarters of the way around its surface. The history behind its formation is unknown, but it is thought that the 100-kilometre (60-mile) wide crack could have formed as the moon cooled, or could have been created during the impact that left the vast Odysseus crater on its leading hemisphere.

Baltis Vallis is a 6,800-kilometre (4,200-mile) channel on Venus. It is the longest in the Solar System, challenged only by the River Nile in Egypt, which measures around 6,650 kilometres (4,132 miles) from start to finish. At between one and three kilometres (0.6 and 1.8 miles) wide, Baltis Vallis is thought to have been formed by fast-moving lava flows, and resembles a river in the way that it winds across the landscape.

97 Painted moon The surface of Saturn’s moon Iapetus is half black and half white, earning it the nickname ‘painted moon’. Its strange colouration is thought to be down to debris sprayed onto its face by other moons. As the dark material is heated by the Sun, any ice trapped with it turns to vapour, leaving just the sooty debris behind and preventing the ‘paint’ being covered with bright ice.

100 Giant Moon

State University; JPL-Calltech; Peter Tuthill & James Lloyd; DLR (German Aerospace Centre); Steveroche; Cassini Imaging Team; SSI;

© NASA; Adam Evans ; Tyrogthekreeper; ESA; ESO; Tobias Roetsch; Planck Collaboration; Ken Crawford; ESO/F. Courbin et al; Arizona

98 Jewel box

Long thought of as the ninth planet, Pluto was demoted to ‘dwarf planet’ in 2006. However, despite its diminutive size, Pluto is still a wonder in its own right. The tiny ball of rock and ice would fit inside the United States, but it manages to hold on to five moons. The biggest, Charon is almost half its size, making it the largest moon relative to its parent body in the Solar System.

The NGC 3603 nebula is home to one of the most massive clusters of young stars in the Milky Way. Just 20,000 light years from Earth, the open cluster is described by NASA as a ‘stellar jewel box’, with three truly massive Wolf-Rayet stars nestled at its core. The hot young stars have blown away their blanket of dust and are blasting the surrounding hydrogen gas with ultraviolet light, illuminating the clouds.

99 Six-star system The Castor star that makes up the head of one of the twins in the constellation Gemini, is not quite what it seems. It is actually a complex system of six separate stars. Castor A and B are a binary system, a pair of orbiting stars, but each is orbited by another dwarf star, Castor Aa and Castor Bb. This system of four stars is then orbited by another binary pair of dwarf stars, known together as Castor C.

21

Exploration

Missions to the planets, our cosmic back yard and beyond 24 10 daring space rescues

From fearless spacewalks to death-defying descents to Earth

34 Mapping the Milky Way

How the telescope Gaia is scanning the skies

42 The search for New Earth

Will our searches ever lead to the discovery of an Earth 2.0

50 Interstellar space travel

The science behind the warp drives that could take us to the stars

“Astronomers have only catalogued a tiny fraction of the 100 billion stars in our galaxy”

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Mapping the Milky Way 22

24

10 daring space rescues

42

Searching for New Earth

50

Interstellar

©NASA, ESO

space travel 23

1DA0RING SPACE S E U RESC

escents to d g in fy e -d h t a cewalks to de of heroism that brought a p s s s e rl a fe From ith stories w d e ll fi is e c disaster a ra e n f o k Earth, sp in r b from the missions back

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10 daring space rescues

25

Exploration

1

Apollo 13

Disaster date: 13 April 1970 What happened: A faulty oxygen tank turned the third manned mission to the Moon into an epic fight for survival

In April 1970, John Swigert, Fred Haise and James Lovell left Earth on a mission bound for the Moon. After 55 hours the crew took part in a live television broadcast back to Earth, but just nine minutes later, disaster struck. Ground tests before the launch had revealed a problem with oxygen tank 2. It had been used previously on Apollo 10, but had been damaged and had undergone repairs. Before launch, it would not empty properly, so engineers used the internal heater to boil off the extra oxygen. Unbeknown to them, during the procedure, the on-off switch became welded shut.

The fault went unnoticed and during the flight the temperature inside the tank skyrocketed. When the crew stirred the tanks 56 hours into their mission, they didn’t realise that the insulation on the electrical wires inside had melted. As the fans turned, the wires touched, shorting out and setting the insulation alight. The astronauts heard a loud bang and felt the spacecraft rumble. Swigert contacted mission control and said the famous words, “Houston, we’ve had a problem here”. The oxygen dials showed that one tank was empty and the level in the second was falling.

Mission timeline 8. Return home

Time: 142:40:45 Apollo 13 re-entered the atmosphere almost four days after the disastrous explosion, carrying the exhausted crew to a gentle ocean splashdown.

Powering on Earth

Time: 140:10:00 The Command Module was brought back online shortly before the crew reached Earth.

The crew had trained in simulations and remained calm, but tank one had also been damaged and their oxygen supply was rapidly running out. Before launch, the crew had practised using the Lunar Module as a lifeboat in case of emergencies. It carried enough oxygen and battery power for almost two days. With just a few minutes of power left the crew shut the Command Module down and transferred to the Lunar Module. Mission control calculated that it would take two five-minute burns to loop Apollo 13 round the far side of the Moon and back towards Earth, but it would take several days to rescue them. The Lunar Module had only been designed to operate for two days. The temperature plummeted and the men had to drastically cut their water intake and they barely slept as they returned towards the Earth. The Lunar Module was not heat shielded, so in order to re-enter Earth’s atmosphere, the crew had to return to the Command Module. It’d never been switched off during a mission before but as they approached Earth, the astronauts managed to successfully power the module back on. As the crew dropped through the atmosphere, communications cut out and mission control held its breath. Finally, they received confirmation that everyone was alright and the astronauts had splashed down safely in the Pacific Ocean.

7. Assessing the damage Time: 138:01:48 The damaged service module was released into space, and the crew were able to view the extent of the explosion for the first time.

“Mission control held its breath as the crew dropped through the atmosphere”

1. Lift-off

Time: 00:00:00 Apollo 13 was the third manned mission to the lunar surface, and the crew planned to explore the Fra Mauro region on the near-side of the Moon.

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2. Television transmission

Time: 55:14:00 Shortly before the explosion, the crew took part in a live television broadcast back to Earth, showing viewers what life was like inside the module.

10 daring space rescues

The Apollo 13 crew had to make use of the Lunar Module (on the left) in their fight for survival

NASA’s Apollo 13 report

6. Running repairs

Time: 93:30:00 After just a day and a half in the module, carbon dioxide levels rose dangerously high, and mission control had to invent a quick fix to replace the filters.

5. Emergency correction

Time: 61:29:43 The crew executed the first burn to swing Apollo 13 around the Moon and back towards the Earth.

4. To the lifeboat

Moon

Time: 57:43:00 As the remaining oxygen dwindled, the crew abandoned the Command Module and retreated to the safety of the Lunar Module, which had its own separate supplies.

3. “Houston, we’ve had a problem”

Time: 55:55:20 After the broadcast had ended, the crew were asked to stir the oxygen tanks. Tank two was faulty, and the procedure triggered a catastrophic explosion in the support module, venting their vital oxygen supply and taking the fuel cells offline.

d mission which aborted man’s thir The Apollo 13 accident, r of the inde rem sh har a is n, the Moo to explore the surface of g. kin erta und immense diff iculty of this ch veh icle, of ground complexes, laun The tota l Apollo system demand ing and s itiou amb t mos the and spacecraft constitutes . For these t ever underta ken by man eng ineering developmen t perform to mus ent ipm men and equ missions to succeed, both resu lted in two ady alre has em syst nea r perfection. That this to those men and explorations is a tribute successful luna r surface it. flew and t, buil designed, women who conceived, icult to icult to ach ieve, but diff Perfection is not only diff a nea r uted stit con n in Apollo 13 mai nta in. The imperfectio ance on the par t form per g din tan outs the disaster, averted only by suppor ted them. und control team which of the crew and the gro the with rged cha rd was The Apollo 13 Rev iew Boa rou ndin g the sur ces tan ums circ the ing responsibilities of rev iew accident, of the of g the probable causes accident, of establishin , of reporti ng ons acti y ver reco ht ss of flig assessin g the effectivene corrective for ns eloping recommendatio these find ings, and of dev ry out car to rt effo ry eve rd has made or other actions. The Boa al man ner. In arti imp and e, ctiv obje ough, its assignment in a thor re ana lyses and e effective use of the failu doin g so, the Boa rd mad Spacecraft ned Man the by car ried out corrective action stud ies ication and objectiv ity ded the with ed ress Center and was ver y imp

of this effort. equ ipment nature of the Apollo 13 The Boa rd feels that the to futu re lied lessons which, when app failu re holds importa nt ss of man ned ene ctiv effe and to the safety missions, will contribute space flight.

27

Exploration

2

Rosetta/Philae Disaster date: 12 November 2014 What happened: The ten-year mission to land a probe on a comet came close to failure when the harpoons designed to anchor the Philae lander did not deploy

The Rosetta spacecraft had chased comet 67P/ Churyumov-Gerasimenko for over ten years, travelling 6.4 billion kilometres (4 billion miles) before coming into orbit on 6 August 2014. The next phase of the mission was to soft-land the Philae probe on to the surface so that it could sample the comet with its on-board laboratory. The team aimed to slow the probe to one metre (3.3 feet) per second as it neared the surface, allowing its three legs to land gently on a flat patch of ground. Harpoons would then be deployed to bolt the lander to the floor. However, when Philae touched down it did not quite go as planned. The anchoring harpoons did not fire and instead of landing safely, Philae bounced off, skipping twice like a stone before coming to rest. The surface of the comet was a dangerous combination of jutting rocks, boulders and plumes of gas and dust, and when Philae returned its first images, it became clear

that it was tilted sideways in the shadow of a cliff with one of its legs up in the air. Having bounced away from its planned landing site, scientists on the ground had no idea where the probe had eventually touched down. Without enough sunlight, Philae was in danger of running out of battery and in its precarious position, any manoeuvre could knock it over completely or worse, propel it out into space. However, despite these problems, Philae completed its first set of science experiments, providing an incredible wealth of new data. Philae’s primary batteries ran down after 57 hours, at which point it entered hibernation mode. But before it went to sleep, scientists tried a bold rescue operation. They lifted the probe by four centimetres (1.6 inches) and rotated it by 35 degrees in the hope that with the solar panels repositioned, it might be able to wake up as the comet gets closer to the Sun.

With very little gravity on the comet, Philae is about the same weight as a paperclip, and this image captured by its camera reveals its precarious position

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Time: 09:03 GMT The Philae lander was released from Rosetta 22.5km (14mi) away from the surface of the comet.

2km

Descent

1.5km

Duration: 7 hours Philae arrived at the planned speed of 1m (3.3ft) per second after seven hours of descent.

1km

0.5km

Spirit rover Disaster date: 1 May 2009 What happened: After five years on the surface of Mars, NASA’s Spirit rover became lodged in a sand trap

In the spring of 2009, NASA’s Spirit rover was investigating a location on Mars known as Troy, but the ground was softer than it appeared. In 2006 Spirit’s right front wheel had stopped working, and as the top layer of soil gave way, the stuck wheel churned the ground and Spirit started to sink. NASA engineers built a sandy testbed to replicate Spirit’s predicament, and began testing different combinations of backwards driving and wheel wiggling to try to find the best way to free Spirit. Attempts to rescue the rover began on 16 November 2009, but after three days it had only moved forwards by 12 millimetres (0.5 inches). The rear right wheel stalled repeatedly and after just a

2.5km

Separation

few attempts, it gave up altogether. With just four wheels remaining, and with winter fast approaching, the team feared that soon the rover would no longer be able to capture enough solar energy. They tried driving backwards, and managed to climb up for the first time, but progress was painfully slow and after eight months the rover was still trapped. Winter eventually hit and Spirit entered hibernation, but unfortunately, contact never resumed. However, in the process of getting stuck churning up the soil, Spirit had released sulphates hidden beneath, revealing evidence of a nearby steam vent and providing new clues about the water cycle on modern Mars.

During its time on Mars, Spirit uncovered evidence of water, volcanic activity, and hydrothermal vents

10 daring space rescues Air time First bounce

Time: 15:34 GMT The harpoons designed to bolt Philae to the comet did not deploy, and the probe bounced away from the surface.

Duration: 1 hour 50 minutes Following the first bounce, Philae reached a speed of 38cm (15in) per second. Had it reached 50cm (19.7in) per second, it would have escaped the comet’s gravity.

Second bounce

Time: 17:25 GMT After travelling around 1km (0.6mi) across the comet’s surface, the lander came down and bounced again.

Air time

Duration: 7 minutes The second bounce was much shorter than the first and saw Philae land in a precarious position.

Final position

Time: 17:32 GMT Philae ended up tilted sideways in the shadow of a cliff but nevertheless, was able to perform the science that enabled Rosetta to successfully complete its primary mission.

4 Apollo 11 Disaster date: 24 July 1969 What happened: Buzz Aldrin and Neil Armstrong were almost stranded on the Moon after the switch that armed their ascent engine broke

2.5km

The Spirit rover became stuck in soft soil at the edge of a crater, and despite months of rescue attempts was unable to break free

The Moon landing was one of the most monumental days in human history, but there were some tense moments along the way. The descent was challenging, and amid problems with communications and the on-board computer, Armstrong and Aldrin overshot their landing zone. They eventually touched down with less than 30 seconds of fuel remaining. After their historic moonwalk, the two astronauts returned to the lander, but in the process one of their life support backpacks nudged the switch that armed the ascent engine and snapped it off. Without it, they wouldn’t be able to return to the waiting orbiter. Ground control quickly replicated the fault on a mockup of the module on Earth, and set about finding a way to flick the switch using any available objects. Luckily, the astronauts were carrying pens, so Aldrin was able to use one to push the switch, arming the engine and saving the day.

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Exploration Space Shuttle Endeavour carried seven crew members to Hubble and after five separate spacewalks, the telescope was fixed

5

Hubble Space Telescope Disaster date: 20 May 1990 What happened: The iconic Hubble Space Telescope almost became one of science’s biggest mistakes when it was launched into space with a faulty mirror

The Hubble Space Telescope has captured some of the most iconic images ever taken of outer space, but it started out with a major fault. The project had cost billions of dollars and carried a meticulously polished 2.4-metre (7.9-foot) mirror weighing just over 800 kilograms (1,800 pounds). Free from the interference of Earth’s atmosphere, Hubble was expected to return high-resolution images but after the first images were returned just a few weeks later, it became clear that something was wrong.

The primary mirror had a flaw known as a spherical aberration; the edges were too flat, which meant that the light was not properly focused, causing a fuzzy halo to appear in every image. There was public outcry, and NASA came under attack for wasting money on a scientific disaster. So, in 1993, NASA attempted to save the ailing space telescope. Seven crew members carried with them the Corrective Optics Space Telescope Axial Replacement (COSTAR). It was made up of five pairs

The mirror flaw

Spot the difference

of mirrors that, when installed in front of the Faint Object Spectrograph, the Goddard High Resolution Spectrograph and the Faint Object Camera, would work like a pair of glasses to bend the light, bringing it into focus. They also took the Wide Field Planetary Camera 2, which included its own corrective optics, and boosted Hubble’s ultraviolet vision. The astronauts spent 11 months training and practised the fiddly procedures over and over again inside a special water tank. The mission was a resounding success but during the final stages, while changing some insulation, a tiny screw floated away. Fearing that it could dent the new mirrors, the crew had to use the Shuttle’s arm to capture it. This before and after image of the nucleus of the M100 galaxy reveals the full extent of Hubble’s mirror fault

Actual shape Intended shape

Four microns too flat at the edges 30

BEFORE

AFTER

10 daring space rescues

Flying solo

Leonov decided not to tell ground control about his predicament, and made the decision to let the air out of his suit alone.

Inflated suit

The gloves and shoes attached to Leonov’s suit had expanded away from his body, and he was unable to bend his limbs to get back inside the airlock.

6

Inflatable airlock

Voskhod 2

Leonov was supposed to re-enter the airlock feet first, but he ended up having to pull himself in the wrong way round.

Disaster date: 18 March 1965 What happened: The first-ever spacewalk almost ended in tragedy when Alexei Leonov’s spacesuit expanded, preventing him from fitting back inside the airlock

In 1965, Alexei Leonov became the first man to ‘swim in space’. He had trained for 18 months for this 12-minute spacewalk, and his superiors were so afraid that something might go wrong that they reportedly provided him with a suicide pill in case he was unable to re-enter the spacecraft. By the time Leonov had completed his spacewalk, the air inside his suit had expanded in the vacuum of space. Moving became difficult, and when he tried to return to the airlock he realised that he could no longer fit inside. Leonov was running out of time and realising the severity of his situation, he tried something brave. He began to deflate his suit, risking his oxygen supply by releasing the gas into space. He managed to squeeze back into the airlock but in the process lost six kilograms (13 pounds) in body

During a spacewalk on the ISS, water started to build up inside Luca Parmitano’s faulty helmet, clinging to his eyes and nose

weight, and emerged covered in sweat. Unfortunately, this was not the end of his traumatic ordeal. The automatic guidance system on board the spacecraft was not working, so the crew needed to navigate re-entry into the Earth’s atmosphere manually. As they descended the craft began to spin. They veered off course and came down in the icy wastelands of the taiga forests of Siberia. The spacecraft eventually crash-landed in an area that was so inaccessible that the rescue helicopter was unable to land. Instead, they dropped supplies and the cosmonauts had to spend two nights in the forest with an open hatch, braving bears, wolves and the elements, before the rescue team accompanied them as they skied to the nearest landing point for evacuation.

Chest camera

Leonov carried a chestmounted camera, but his suit had blown up so much that he could not bend to reach the shutter release on his leg. Before his suit inflated, Leonov was able to attach a video camera to the end of the inflatable airlock, capturing images of his historic spacewalk and the Earth below

7 ISS helmet malfunction Disaster date: 16 July 2013 What happened: An ISS spacewalk was abruptly cut short when Luca Parmitano’s helmet started to fill with water During a spacewalk on the International Space Station, Luca Parmitano realised that something wasn’t right. He could feel water creeping across his communications cap, and it soon became clear that he needed to go back to the airlock. As Parmitano tried to climb back, the Sun set, plunging him into almost total darkness. He later told us, “It’s a black like nothing you can experience on Earth.” Guided only by a 30-centimetre (12-inch) ring of light from his helmet and with water

covering his eyes and nose, Parmitano had to navigate across a ‘no-touch zone’. “I was upside down with no light, no eyesight because my eyes were covered, I had water in my nose and I tried to call the ground and Chris, but neither one could hear me.” Parmitano decided to return to the airlock unaided and five minutes later he was inside. “The next thing I knew Chris was squeezing my hand trying to get a response and my response was to squeeze as hard as I could to give him the okay.”

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Exploration

8

Progress-Mir collision

Disaster date: 25 June 1997 What happened: The crew of Mir faced catastrophe as a bus-sized supply freighter punched a hole in the Russian space station In 1997, Russian cosmonaut Vasily Tsibliev was in charge of docking the supply freighter Progress with the Mir Space Station. It was his job to guide Progress in, using an on-board camera to navigate. However, the slow pictures made judging the speed of the craft difficult and, as Progress headed towards Mir, it began to move too fast. Cosmonaut Aleksandr Lazutkin saw the craft approaching and sounded the alarm. Even though Tsibliev had fired the braking rockets, it was too late and Progress slammed into Mir’s Spektr module, crashing through the solar array and tearing a hole in the hull.

The crew worked rapidly to cut the connections to the damaged module. Pressure inside stabilised and the immediate danger was over, but the impact had set Mir spinning wildly, preventing the remaining solar panels from facing the Sun. Working together with Tsibliev, who was now at the controls of the docked Soyuz, astronaut Mike Foale shouted instructions to fire the thrusters to bring the spin under control. As they passed over the sunny side of the Earth, they managed to charge the batteries and to the relief of all, the space station came back to life.

The Progress freighter slammed straight into the Spektr module on Mir. The solar panels were crippled and a hole was punched through the hull

1. Progress approaches

2. Braking rockets fired

3. Progress-Mir collision

4. Mir in a spin

Watching the Progress freighter coming in on the video monitor, Vasily Tsibliev did not realise that it was picking up speed and approaching Mir too quickly. The seven-ton craft was on a course for collision.

Aleksandr Lazutkin saw Progress approaching and sounded the alarm just before the freighter collided with the Spektr module. The pressure started to fall, and the three men had to work rapidly to seal off the damaged part of the station.

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Tsibliev fired the on-board braking rockets to slow Progress down, but they were small and weak, and there was not enough time to slow down before the freighter reached the hull of the space station.

The collision set Mir spinning, preventing light from reaching the solar panels. Using an old sailing technique and some quick maths, Michael Foale managed to calculate the amount of thrust required to correct the spin.

10 daring space rescues

9

Space Shuttle Discovery

The crew had to fix the heat shield problems before returning to Earth

Disaster date: 26 July 2005 What happened: During the launch of the first Space Shuttle flight after the 2003 Columbia disaster, the heat shielding on the underside of the craft was damaged

In 2005, NASA’s Space Shuttle Discovery travelled to the International Space Station to deliver supplies and equipment, but during launch the craft sustained some damage. Several chunks of insulating foam broke away from the Shuttle, and some of the ceramic gap fillers that stop the heat shield tiles from rattling managed to wriggle free. Engineers were concerned that these uneven bumps would cause turbulence as the craft re-entered Earth’s atmosphere, and projected that the damage could increase heating by up to 30 per cent, potentially putting the lives of the crew in danger. Just two years earlier, Space Shuttle Columbia had broken up on re-entry following damage to its heat shields, tragically ending the lives of its seven crew members. After this tragedy, ground control was not happy to allow the Discovery crew to return to Earth until the damage had been fixed.

A repair mission was included during the third and final spacewalk, but nothing like it had ever been attempted before. The underside of the Shuttle was fragile and astronauts had never been allowed so close to the heat shielding tiles before. As a consequence, no handrails had been built in for support, so astronauts Steve Robinson and Soichi Noguchi had to ride on the International Space Station’s Canadarm2 robotic arm to reach the damaged area. Robinson was to perform the historic repair and he carried a pair of forceps and a saw with him, in case the ceramic fabric was difficult to remove. But in the end he found it simple enough to ease them out with his fingers. As he triumphantly removed the second piece he said, “it looks like this big spaceship is cured”. The Shuttle was later cleared for re-entry, and returned safely to Earth on 9 August 2005.

“Ground control wouldn’t let Discovery return to Earth until the problem was fixed”

NASA astronaut Steve Robinson captured this close-up image of Discovery’s heat shields as he performed the vital repairs

10 Liberty Bell 7 Gus Grissom had been on a 15-minute suborbital flight and had splashed down in the Atlantic Ocean. His capsule, Liberty Bell 7, was fitted with a new explosively activated escape hatch at the side but as he waited for the helicopter, it burst open and water flooded in. Grissom escaped as the capsule started to sink but he was left floating in the open ocean. He had also forgotten to close the oxygen inlet to his suit and water was trickling in, weighing him down.

Unaware of his immediate peril and thinking that the spacesuit would keep Grissom afloat, the helicopter pilot attempted to rescue the sinking capsule first. But Liberty Bell 7 kept refilling as the waves swelled, and the helicopter could not take the strain. After a tense four minutes and with Grissom close to drowning, the sinking capsule was abandoned to the waves, and a second helicopter was called to pluck the exhausted astronaut from the water.

The hatch on Liberty Bell 7 flooded with water each time the waves swelled, and the helicopter’s engine almost cut out

© Adrian Mann; NASA; ESA; Getty; Roscosmos

Disaster date: 21 July 1961 What happened: One of the first-ever suborbital space flights almost ended in disaster when the escape hatch blew open prematurely, flooding the capsule in the middle of the ocean

With the first helicopter in a bad way, a second rescue pilot had to be called to pull Grissom from the Atlantic Ocean

33

MAPPING THE

MILKY WAY

A billion stars… and a billion-pixel camera. The space telescope Gaia is scanning the skies to make a vast 3D map of the Milky Way

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Mapping the Milky Way There are 100 billion stars in our galaxy but, to date, astronomers have only catalogued a tiny fraction of them. Using a satellite called Hipparcos launched by the European Space Agency (ESA) over 20 years ago, the position of celestial objects in the sky were measured 200 times more accurately than ever before. But before that mission had even come to an end, ESA’s scientists were discussing the next step. In 1992, the idea of launching a technically superior spacecraft capable of mapping - literally - a million times more of the Milky Way than ever before was floated. This would eventually become the Gaia mission, the most ambitious plan to map our galaxy that has ever got off the ground. Gaia was launched in December 2013 via a Russian Soyuz/ST rocket from Kourou, French Guiana, and its goal is to create an accurate 3D map of the Milky Way by plotting the positions of a billion stars, the equivalent of one per cent of the universe. As well as being able to collect more than 30 times the light of Hipparcos, its reach will extend beyond the galactic centre with measurements that will have an accuracy 200 times greater than Hipparcos was able to achieve. As a result, it will generate 50 gigabytes of data each day – a total of 100 terabytes once the mission has ended. And for the 2,500 people working on Gaia – from ESA’s staff and members of the space industry to those in academia and the scientific community – it will address key issues about our galaxy that have, until now, always seemed out of reach, something which excites project scientist Dr Timo Prusti. “The motivation has always been to discover the structure of the Milky Way,” he says, having worked on the Gaia mission since 2007. “We can see all of these beautiful pictures from the Hubble telescope of external galaxies but we don’t know how our own galaxy looks. Where are the spiral arms? Are we in the middle of a big spiral arm? With Gaia, we can get a correct picture; the basic information.” In order to carry out its work, Gaia had to reach its designated orbit 1.5 million kilometres (932,000 miles) from Earth. It did this in January 2014, arriving at a location known as Lagrange point 2 (L2) where the combined gravitational pull of the Sun and the Earth is neutral. This location allows for eclipse-free observations, creating the perfect vantage point for the craft to view the galaxy and it is important that it remains there, prompting the need for fine adjustments to be made each month using its built-in thrusters. Scientists then began calibrating Gaia’s two telescopes and three instruments. Almost immediately, they began to see results. Gaia was able to take test images, one of which showed a cluster of stars in a satellite galaxy of the Milky Way called the Large Magellanic Cloud. The best, however, is yet to come. In July, with the tests and the calibration complete, 3D mapping finally started. Rather than take

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Exploration

Gaia’s Deployable Sunshield Assembly (DSA) was folded against the spacecraft’s body for launch. An hour later, it was deployed

Fast facts

Gaia will also be able to spot thousands of asteroids, comets, failed stars, new planets, exploded stars and variable stars. Phew.

Sun

Moon 150 m illion km

Earth

Moon

1.5 m illion km

L2

Gaia orbits a point in space 1.5 million km (932,000 mi) from Earth known as L2

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simple snapshots, the main aim is to measure the distance between the stars. This not only plots their coordinates but it helps astronomers to determine each star’s essential properties, giving a firm idea as to their true luminosity, age and mass. To do this, Gaia absorbs a huge amount of data as it orbits. It spins slowly once every six hours, scanning the sky in any direction. Its two telescopes simultaneously observe two rectangular patches of the sky and it uses a quantity called the stellar parallax which, using simple geometry, can be converted into distance. “It’s a triangulation, where we are observing a star from two positions,” says Dr Prusti. “When Gaia is at L2 we measure that moment of time. Six months later, Gaia moves with the Earth to the other side of the Sun and it takes a second measure.” Both times, light is focused on the charge-coupled device (CCD) camera which covers an area of 0.38m 2 (4.1ft2). Not only is the camera capable of taking images to 1 billion pixels, it’s the largest focal plane ever flown in space. It can detect stars down to magnitude 20 – 400,000 times fainter than the naked eye could see. “These are very faint objects,” Dr Prusti asserts. The Gaia spacecraft is a technical marvel, costing around £640 million ($1 billion) to build. Standing at three metres (9.8 feet) in height and weighing

Mapping the Milky Way

Gaia’s goals

If ESA’s astronomers manage to achieve everything they set out to do, Gaia will hit the back of the net

Measuring the precise distance of stars

Creating a 3D map of the Milky Way

Revealing the physical properties of stars

Yielding clues about dark matter

Discovering previously unknown objects

Since Gaia will observe each star around 70 times over a five-year period – and because it is sensitive to parallax – it is able to take very precise measurements, pinpointing the positions of our galaxy’s stars and looking at their distance from each other. This will allow scientists to gain a snapshot of the Milky Way as it appears now. But Gaia will also study each star’s motion and this will answer questions about the galaxy’s origin and evolution. What’s more, scientists will be able to predict the future of the galaxy based on these movements.

Although we have a good idea of how our galaxy looks, until now no one has attempted to chart its true structure. But in creating a 3D map of the Milky Way, Gaia will plot a billion stars, a feat that will, no doubt, see a mass redrawing of astronomy books and star charts. The result will be the most complete 3D map of the Milky Way ever produced, even bettering that of Hipparcos which produced an catalogue containing some 118,000 stars. Simply knowing basic information about the kind of galaxy we live in will be incredibly useful for scientists.

Spectrophotometric measurements are being taken by Gaia to help scientists learn about each star’s gravity, luminosity, temperature and chemical composition. When combined with the movement of the stars, astronomers will also be able to work out which star families belonged to different galaxies outside the Milky Way; that is, those which have since been consumed by our galaxy. As well as giving scientists a better understanding of how galaxies work, this kind of data will also give a greater insight into the origins of the Milky Way.

The nature of dark matter has long been a mystery and astronomers are still to crack just what this invisible stuff is that makes up the bulk of the universe. Gaia will be able to study dark matter’s distribution in the galaxy and while it’s not a primary aim, it should at least shed new light in the wake of findings from the ESO's (European Southern Observatory's) La Silla telescope in Chile, which scanned 400 stars close to the Sun and found no evidence of dark matter. Only by observing dark matter’s gravitational effects on its environment, will further questions be answered.

Although Gaia was not created to find planets outside of the Solar System, the discovery of such objects around other stars is important in current science. Researchers from Princeton University in the US and Lund University in Sweden say there is no reason why Gaia cannot, as a by-product, be repurposed to allow such discoveries. They believe, over five years, that Gaia will be able to detect as many as 21,000 exoplanets. Certainly, Gaia’s project scientist Dr Prusti says the mission could discover larger, Jupiter-like planets as well as a number of new asteroids.

two tons, it has three main components. The service module is, in effect, the engine room which houses equipment to control and operate the satellite and a communication subsystem. As well as supporting the payload module, providing power, video data processing and data storage, it also has a high rate data telemetry, star trackers and a central computer and data handing subsystem. The payload module includes an instrument with three functions. The main one deals with astrometry, measuring star position, motion and parallax distance. To do this, Gaia needs to collect as many photos of the stars as it can so the positioning can be determined as precisely as possible. There’s also a photometric function which informs astronomers of the light wavelengths a star is emitting. This gives clues as to a star’s temperature and its constituent atmosphere. It also indicates the pressure on it.

A spectrometer observes the Doppler shifts (or change in frequency of a wave) in the spectrum of a planet’s star. Finally, to ensure the satellite is protected from intense heat, the satellite has a deployable sunshield which opens up to a diameter of ten metres (33 feet). “As time went on, the technology became available to ensure the mission would not be an impossible one,” Dr Prusti says. Perhaps the most astonishing thing, however, is Gaia’s ability to measure the motion of the stars. Since each star will be observed, on average, 70 times over the course of the mission, astronomers can study their velocity. And because each celestial object preserves a part of the era in which it was born, scientists can decipher where the star was millions of years ago. They will also be able to say where it will be in the future. “It allows us to look back in time and it gives us an idea of the galaxy’s history,” says Dr Prusti. “We will be able to work out how the Milky Way was formed and predict where it is going

“It allows us to look back in time and gives us an idea of the galaxy’s history” Dr Timo Prusti

A stellar nursery in the Large Magellanic Cloud, a galaxy near us that scientists used to help calibrate Gaia

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Exploration

The reach of Gaia

Able to gather more data than any other satellite ever created, Gaia can peer deep into the darkness of the Milky Way

Fast facts

Gaia will measure a billion stars – including our closest, Proxima Centauri. That’s one per cent of the total star content of the Milky Way.

The Sun

Lagrange point

because we will know how the stars are moving.” Plotting this star-studded family tree, of course, takes time which is why, despite the entire sky having been scanned at least once already, ESA’s astronomers don’t expect to see a reasonable, usable map of the sky to start emerging until the summer of 2016. Even then, a full astrometric catalogue is unlikely until 2017 at which point there will be a good knowledge of the motions. The remaining time of the mission will be spent improving accuracy of the data. But in the meantime, some fundamental finds are emerging. In August, two observations taken a month apart saw a sudden rise in the brightness

Gaia is located 1.5 million km (932,000mi) from Earth, orbiting around Lagrange point 2 – a place where the gravity of Earth and the Sun are balanced.

of a distant galaxy 500 million light years from Earth. Gaia had, it very quickly emerged, just discovered its first stellar explosion. “We can now look at what we saw last time – maybe two weeks or a month ago – and look for changes,” says Dr Prusti. “Then we can make an alert to say, ‘okay, something interesting happened in this part of the sky’.” Gaia will also be charting whatever flashes into its path and these images can be immediately transmitted back to Earth via high frequency radio waves. The satellite doesn’t send every piece of information it absorbs to scientists on Earth; instead it

“If there are any asteroids in strange orbits… we will see them first because nobody is searching for them” Dr Timo Prusti 38

Previous missions have only been able to measure the distance to stars that are up to 326 light years away. That’s 100 parallax seconds, or parsecs, from the Sun.

looks for stark changes which ensures that scientists are quickly alerted and can then follow it up. As a result, astronomers are expecting to detect a number of new asteroids (especially watching for any that may threaten Earth) and it is, space experts assert, best placed to do this, particularly because it can observe at a 45-degree angle from the Sun. “The interesting thing with a 45-degree angle observation is that we are looking inside the orbit of Earth itself,” says Dr Prusti. “If we have any small asteroids locked on the same orbit as Earth, we are going to find them with this scanning method. Gaia also has an advantage over most of the ground base searches for new asteroids which concentrate on the ecliptic plane. They don’t look at the full sky. They look to places where there is the highest probability to find something new. But for the main goal of Gaia, we need to look at the whole sky so if there are any asteroids in very strange orbits, sort of out of the ecliptic plane, we will see them first because nobody else is searching for them.” It will also be possible for Gaia to discover large planets, albeit those similar to the Solar System’s

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Far seer

Gaia can take in so much more. It can measure stars with an accuracy of ten per cent up to 10,000 parsecs (over 32,000 light years) away.

Mapping the Milky Way

Outer reaches

Being able to detect stars at this range – 20,000 parsecs or some 65,231 light years away – is a remarkable feat for any instrument.

Globular clusters orbit in large groups close to the galactic core

Motion measurement

Disc dynamics

The Milky Way is a disc-shaped structure. Gaia will look at the spiral arms (regions of stars extending from the centre).

Although Gaia will not be measuring distances at this point in the Milky Way, it will be studying motions to an accuracy of 1km (0.6mi) per second.

Globular clusters There are at least 100 billion stars in the Milky Way and Gaia is mapping just one per cent, or 1 billion, which shows the sheer scale of our galaxy

Jupiter (Gaia is not sensitive to small planets). In particular, Gaia will pick up on planets that have a five to ten year orbital period around their host star. It will also be able to discover icy bodies in the outer Solar System, comet showers, space warps, brown dwarfs (low-mass planets that emit little light), quasars and visible galaxies located billions of light years away. And it will also be able to detect dark energy, albeit indirectly, as well as dark matter. It can do all of this with clear vision. Gaia’s position in the sky means it does not have to contend with atmospheric disturbances. “We’re observing the whole sky under the same conditions that the atmosphere does not disturb,” says Dr Prusti. “This isn’t possible with a ground-based telescope, no matter how big it may be. The atmosphere will also cause a problem.” And yet Gaia has not been entirely without its own challenges. Aligning and focusing the telescopes was a difficult and time-consuming exercise which caused the commissioning phase to last a month longer than originally anticipated. “We had to take a very systematic step-by-step approach to get them aligned,” Dr Prusti says.

These are spherical collections of stars orbiting a galactic core. There are as many as 158 known in the Milky Way and up to 20 undiscovered.

In order for the mission to run smoothly, Gaia’s mission control team carried out a series of launch simulations at ESA’s European Space Operations Centre

Fast facts

Gaia has started to take measurements (200 times more accurately than Hipparcos) and it will continue to do so for a period of five years.

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Exploration

Fast facts

Gaia launched on 19 December 2013 as a fully European mission and it took a month to travel 1.5 million km (932,000mi) from Earth.

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Gaia’s launch, from Kourou in French Guiana

“Do you really need 1 billion stars? Isn’t 1 million enough?” Dr Timo Prusti

Worse, shortly after it was commissioned, a steady drop in the transmission of Gaia’s telescopes was spotted. Trapped vapour following the satellite’s launch had caused water ice deposits to build up on the mirrors. This was resolved by heating the payload so that the ice melted away from the optics but there was still a concern that stray light was hitting parts of the Gaia focal plane. ESA reported in a blog post that some of it was diffracting around the edge of the sunshield and being enhanced by reflections off ice deposits. “It was hoped that the decontamination campaign would remove this ice layer, but unfortunately the stray light is still there at the moment,” ESA said in April. “We still have unexpected contamination and we’re getting some water and gas in to the payload elements which are building up very slowly – yet fast enough, for there to be a need for a decontamination exercise in a few months,” Dr Prusti says. “Water in the form of ice is collecting on the mirrors and we don’t really like to heat them because it disturbs our scientific measurements. But we have to do it or the quality of the data will not be good enough.” It hasn’t been the only issue but it has been a major one. “There has been nothing like a showstopper as one can imagine because we are in space at the moment,” Dr Prusti continues. “But clearly there were many challenges. Getting all of the mirrors polished took longer than anticipated but we coped with any issues as they came.” The upshot of the ice problem, however, is that Gaia may not be seeing as faint a light as astronomers would like but ESA insists this aspect is a minor setback. “The more serious one is that the sharpness of the image is not as good as with clean mirrors. We need very sharp images because we try to determine the position of the centroid of a star.” And yet it was never going to be easy. As anyone who takes photos knows, you shouldn’t move when you snap away. But Gaia’s cameras are attempting to match the scanning speed of the sky. Scientists have to ensure Gaia is spinning at the same speed so the electronics can effectively read the picture. No wonder then, that the scientists haven’t attempted to stretch the mission beyond charting one per cent of the Milky Way. “There is always that question: ‘you are observing only one per cent? Is one per cent enough?’” says Dr Prusti. “But the other side of that is: ‘do you really need 1 billion stars? Isn’t 1 million enough?’ We are trying to strike the balance between sampling enough of the galaxy but still having a manageable amount of data to get down. We think we have it just right.” There is no doubt, though, that this is a hugely ambitious mission that, despite costing £2 billion ($3.1 billion) overall, will ultimately be very much worth it. Expect to see Gaia’s first catalogue in 2016 and the full catalogue in 2022.

Mapping the Milky Way

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The Milky Way mapper

How Gaia’s satellite has been constructed to create a 3D map of the Milky Way

metres

Not a scorcher

The sunshield keeps the scientific instruments at a constant temperature of -110°C (-166°F), nippier than Antarctica. It has thermal insulation so that it is resistant to temperatures between -170°C (-274°F) and 70°C (158°F).

Huge sunshield

A large cutting edge sunshield made from carbon-fibre reinforced composite protects the Gaia spacecraft during its mission. It’s similar to a big skirt – at 10m (33ft) in diameter.

C-Si

Silicon carbide

Sensitive sensors

Fast facts

Packing light?

The average UK broadband speed is 14.7Mb/sec but while Gaia’s 8.7Mb/ sec may seem slow in comparison, considering it’s beaming from 1.5 million km (932,000mi) away, it’s quite nifty.

,

Data hungry

So much data will be taken by Gaia that, if you were to put everything on to DVD, you would need 200,000 discs: that’s more than 100TB worth.

It gets its power from the Sun. Underneath the sunshield are lots of solar panels that face the Sun, generating a lot of juice.

Strong signal

2

Gaia’s got some payload: ten mirrors, an astrometry function, a photometry function and a spectrometry function all within the one unit on a spacecraft 3m (9.8ft) high.

Snap happy

Chinese manufacturer Oppo may be creating a 50MP smartphone camera but Gaia boasts a photometer with a resolution of 1,000MP. That’s sharp.

© NASA; Adrian Mann; ESA

o

-110 C

The Gaia spacecraft has sensors that are so powerful, they can detect faint objects with a luminosity 400,000 times lower than the naked eye is capable of seeing.

i C-S

The material that goes into making cutting tools and sandpaper is silicon carbide. It’s really tough stuff – a mix of pure silica sand and carbon – and it makes up Gaia’s structure.

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The search for

NEW EARTH

We've found over a thousand exoplanets in our galaxy, with millions more left to discover. So will we ever find Earth 2.0?

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The search for new Earth

“How likely is life to begin? My answer is ‘very likely’, although intelligent life is possibly extremely rare” Professor Brian Cox 43

Exploration The Next-Generation Transit Survey (NGTS), which is sited at ESO’s Paranal Observatory in Chile, will hunt for super-Earth size worlds

Astronomers think it’s out there somewhere. The planet that’s a dead-ringer, or at least close enough in comparison to our very own Earth. The discovery of such a world could provide tantalising evidence that we aren’t alone in the universe and that life, whatever it may look like, can evolve elsewhere. But we’re yet to find this world and the truth is we have barely begun. The first exoplanets of any kind were not discovered until 1992 and there are still hundreds of billions of stars in our own galaxy that we have yet to study. And while we haven’t yet found a planet that could serve as our Earth's doppelganger, we're getting close. The Kepler Space Telescope holds the record for the most planets found. Even before the space

telescope was built and launched back in 2009, astronomers knew what to task the mission with. Kepler was to search for potentially habitable worlds, hopefully like ours. Despite becoming crippled when two of its reaction wheels (which were used for accurately pointing the space telescope) failed, Kepler hasn’t disappointed. “We’ve found [nearly] 2,000 confirmed planets around distant stars” states physicist Brian Cox, “And over a thousand of them have come through Kepler. Although you might say that's not many, even though it’s more than none, which is what it was 20-odd years ago, the statistics are still quite surprising. Now we know that most stars have solar systems. We suspect that there are of the order of tens of billions of Earth-like planets

Top 5 Earth-like worlds Kepler-438b Announced as a confirmed exoplanet earlier this year, this world has a radius of 1.12 times that of Earth. It rests in the habitable zone of its red dwarf (a star that’s cooler and smaller than our Sun) and astronomers believe that this planet is the most Earth-like to date.

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in the Milky Way, not thousands, not millions, but billions of them.” In our search, astronomers have a checklist as to what really determines and therefore counts as 'potentially habitable'. When you compare Earth with the hellish conditions of Venus and the relatively freezing temperatures of Mars, our planet is like paradise and we are in a very good position to be able to work out what conditions might be like on other rocky worlds. For one, our planet rests in what is known as the habitable zone, a midway point that’s not too hot and not too cold for liquid water to exist, thus being at an ideal distance from its star. “It’s true that on our planet there’s enough heat energy to foster bacteria deep down, so when we search

Gliese 667Cc Able to complete one lap around its parent star in just 28 days, Gilese 667C is a red dwarf that lies 22 light years away in the constellation Scorpius. Gliese 667Cc isn’t the only planet that’s a member of this system. One of two confirmed worlds, this rocky super-Earth is at least 3.9 times more massive than Earth.

The search for new Earth Just the right temperature

Conditions for a habitable Earthlike planet

A planet must be at a suitable distance from its star in order to sustain liquefied water. In general, life is able to survive at temperatures between -15ºC (5ºF) and 115ºC (239ºF).

Less than 1.6-times the size of Earth

Astronomers have proven that planets up to 1.6-times the size of Earth generally follow the same processes that made our planet.

The right amount of nutrients

Nutrients are important to maintain life on a planet. Solid planets and moons are usually made up of the same general chemical makeup.

A magnetic shield

To deflect harmful space radiation as well as possible storms from their parent star, an Earth-like planet should have a magnetic field. This shield also ensures that the atmosphere doesn’t whittle away to nothing.

A protective blanket

A world wrapped up in an atmospheric blanket keeps it warm, trapping heat in and keeping harmful radiation out.

for a new Earth, we’ll be looking for one that orbits at a good distance from its star” states evolutionary biologist Richard Dawkins. This is partly the reason we have not found a new Earth just yet. Our exoplanet-finding methods are biased toward finding planets in close orbits around their stars, rather than in orbits far enough away for the temperatures to be balmy, but not too hot for liquid water. That’s not to say we can’t use them to find small planets further from their stars, just that it is more difficult. For example, Kepler has to observe three transits of a planet before it can be considered a real candidate, but a planet like Earth will take several years to make this many orbits. So astronomers watching with Kepler have had to be

Kepler-442b Discovered by NASA’s Kepler spacecraft, Kepler-442b orbits an orange dwarf star 1,120 light years from Earth. It completes its orbit in roughly 112 days and has a radius 1.3 times that of Earth. It is thought to have a comfortable temperature similar to that of our planet.

patient. Finally, they are starting to reap the rewards, spotting alien planets that are looking more and more like Earth, but crucially we have not found one that seems the same yet. This world should be rocky and have a mass that’s not too dissimilar to Earth. It turns out that worlds with low mass are unable to hold on to an atmosphere since they would have a low gravity and a thick atmosphere like Earth’s, which is vital in protecting any life forms from space radiation. According to Dawkins, gravity would also have an effect on the appearance of life should it evolve on a world that’s substantially lighter or heavier than Earth. “Here we can say quite a lot because we understand quite a lot about the effect gravity has

Kepler-62e Astronomers believe that this exoplanet is a water world, a warm place that’s surface is dominated by liquid water. Kepler-62e lies some 1,200 light years away and takes 122 days to complete one lap around its red dwarf host star.

on life,” he says. “A mouse-sized animal, which is on a planet with very strong gravity would have the proportions of a rhinoceros, as the proportions of each part of the body is affected by gravity.” Dawkins adds that under extremely strong gravity, even small creatures would need thick, strong limbs in order to support the weight of their bodies. “If gravity were weaker, an animal the size of a rhinoceros would have the spindly, long legs of a crane fly or a spider,” he explains. Astronomers have found many worlds using Kepler and other planetfinding observatories, which are small enough to be rocky but which are more massive than Earth. These are called the super-Earths. Their stronger gravity means they could easily keep hold of their

Gliese 832c This hefty world orbits a red dwarf star and weighs in at around 5.4-times the mass of Earth. It’s thought that on the whole, this planet has a temperature similar to Earth. Yet with an orbit that sees the exoplanet swing in and out of the habitable zone, Gliese 832c’s climate can vary.

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Exploration

New world hunters

Transiting Exoplanet Survey Satellite (TESS)

A fleet of space missions and ground-based telescopes have scoured the universe in the search for a new Earth and there’s more on the way Kepler Space Telescope

Hubble Space Telescope

Launched back in 1990, Hubble has been imaging the universe for 25 years (see our celebratory feature on page 8). Having a wide range of astronomical pursuits from studying black holes in faraway galaxies to checking out planets in our Solar System, this space telescope only has a limited amount of time to go hunting for exoplanets. Despite being strapped for time, Hubble has made some important contributions in its search for new worlds, helping us discover what a world might be like on the surface.

Kepler is designed to look for Earth-like planets in orbit around other stars and more specifically, in the Milky Way galaxy. Staring at over 145,000 stars to monitor any dips in brightness that may signal the existence of a planet, Kepler has done well in its search for alien worlds as its 1,000th exoplanet was announced in January 2015. After two of its reaction wheels failed in 2013, Kepler watches out for habitable planets around smaller, dimmer red dwarf stars.

Spitzer Space Telescope

Yet to make it outside the confines of Earth’s atmosphere, the Transiting Exoplanet Survey Satellite, or TESS for short, will hopefully begin seeking out alien worlds in August 2017. Using an array of wide-field cameras, the 350kg (772lb) spacecraft will scan nearby stars that could have small planets orbiting them. TESS will be able to work out the size, mass, density and orbits of the planets it finds as well as examine small planets around stars just like our Sun.

The Spitzer Space Telescope mainly observes the cosmos in infrared and was primarily used to peer through layers of gas and dust to look at young and dying stars, as well as the more exotic black holes and active galaxies. The telescope scientists also armed Spitzer with the ability to hunt for distant worlds, a mission that’s now its sole purpose after its hardware was tweaked ten years after the mission made its way into space in 2003.

Ground-based observatories 46

The search for new Earth

Wide Field Infrared Survey Telescope (WFIRST)

WFIRST is currently in its design phase but it is hoped that this space telescope will ambitiously answer basic questions about dark matter and test Einstein’s theory of general relativity. What’s more, the mission tipped for launch in mid-2020 is looking to get direct images of alien planets. WFIRST hopes to also answer questions about potential life elsewhere in the universe and why Earth is so special.

James Webb Space Telescope (JWST)

Astronomers are waiting for October 2018 with bated breath, since it will see the launch of the highly sensitive JWST. The next-generation telescope will have a range of capabilities in its arsenal, with one of its core abilities to be able to understand the origin of Earth-like planets and its potential to support life. The JWST will probe the physical make up of distant worlds in other planetary systems.

New Worlds Mission

It’s quite difficult to get measurements of exoplanets that either orbit too closely to their star or are in orbit around a very bright star. The New Worlds Mission serves as a plan to build a large occulter in space that will block out intense starlight. It’s hoped that it will make use of this space parasol to observe exoplanets with ease.

atmosphere, but this would also mean that life would have to adapt. Detecting planets is one thing, but detecting their atmospheres is another. Astronomers using the Hubble and Spitzer space telescopes have detected molecules of carbon dioxide, methane and water vapour in the atmospheres of some gas giants and a handful of super-Earths, but the smaller the planet, the thinner the atmosphere and the more difficult it is to take the measurements. We don’t know for certain what conditions are like on the exoplanets we’ve managed to detect, but thanks to Kepler, we’ve now got a bagful of planets that are thought to reside in the habitable zone of their star. The Earthliest of these is Kepler-438b, a world confirmed as a near-Earth-sized exoplanet with a radius of around 1.12 times our world's. This is all well and good, except there is one crucial difference between Kepler-438b and our planet. Kepler-438b orbits what is known as a red dwarf, which is a cool and small star, much less impressive than our own Sun. Because red dwarfs are so cool, their surface temperatures are less than 4,000 degrees Celsius (7,232 degrees Fahrenheit), compared to the Sun’s which is about 5,500 degrees Celsius (9,932 degrees Fahrenheit), the habitable zone is much closer to them than it is around a star like our Sun. Kepler-438b orbits its star once every 35 days at a distance of just 24.8 million kilometres (15.4 million miles), compared to Earth’s 149.6 million kilometres (93 million miles). However, this distance from the star leads to some interesting possibilities. The planet has likely become tidally locked where the gravity of its star has interacted with the planet to slow its own rotation down, so that the length of its day becomes equal to its year. This means that it will always show the same face to its star, like the Moon does to Earth. On one hemisphere it will be warm and always daytime, while on the other it will always be nighttime. If there is no atmosphere, the far side will be in a deep freeze, but if there is a thick, Earth-like atmosphere, the warmth of the star could be redistributed around the planet, keeping the night-side warm enough potentially for liquid water to exist. Such a world would therefore not be a true mirror image of our planet, but the conditions could still be similar, with oceans of water and the potential for life. Red dwarfs are the most common type of star in the galaxy, so maybe the potentially habitable worlds in the Milky Way are tidally locked. In that case planets exactly like Earth are actually more rare than we thought. Finding a habitable planet, an 'Earth 2.0', does not necessarily mean there will definitely be life on that world, but Professor Brian Cox is confident that there could be. “How likely is life to begin? My answer is 'very likely', although intelligent life is possibly extremely rare,” he says. The most Earth-like world in the Solar System besides Earth is the Red Planet, Mars. Some scientists speculate that it may have once harboured primitive microbial life-forms, but Mars is small and lost most of its atmosphere a long time ago. If there were ever any life, it probably would have disappeared at the same time. However, Brian Cox doesn’t think we should use the Red Planet as an example of a habitable world.

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Exploration

Goldilocks zone

Hot stars

The ideal location around a star where Earth-like worlds might be found

The habitable zone is the region where liquid water can exist and is further from the star around hot stars, such as those with temperatures exceeding 30,000ºC (54,000ºF).

Sun-like stars

At a distance of 150mn km (93mn mi), Earth rests in the Sun's habitable zone where conditions are just right for life. Our Sun's surface is about 5,500ºC (9,932ºF).

Key Region too hot for liquid water Region just right for liquid water, also known as the habitable zone

Cooler stars

Region too cold for liquid water “Mars is a bit of a red herring because I don’t think it displays any of the characteristics that we should be looking for if we are looking to find life elsewhere in the rest of the universe,” he says. Maybe complex, intelligent life is a bit optimistic, but microbial life, or plant life could exist on another world like Earth. Scientists have even gone as far as to work out what plants on other worlds might be like and have shown that they would not necessarily have green foliage like most plants on Earth. Their colour would depend on two things: the colour of the star and the composition of the planet’s atmosphere which can absorb the starlight.

Evolutionary biologist Richard Dawkins believes that the gravity of a planet determines the appearance of life-forms on an Earth-like world

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Photosynthesis depends on the sunlight it is receiving and on Earth plants absorb the blue light scattered by the atmosphere as well as red light, reflecting away green light. A planet orbiting a hotter, brighter star where there is less red light and more yellow light, for example, might have plants that conduct photosynthesis by absorbing and reflecting different colours. Some scientists have speculated that plants on a world orbiting a red dwarf star, where there is a predominance of red and infrared light, might have black leaves. Alien plants have actually been suggested as a way to detect habitable worlds. If the world were covered in vegetation, the colour of its leaves would stand out when astronomers study the planet’s light. We do not yet have the technology to do this, but future space missions could have. Other biosignatures might include oxygen, carbon dioxide and water vapour in a planet’s atmosphere. Planet-finding missions and projects for the foreseeable future are focused mainly on finding exoplanets rather than characterising them and discovering if they are habitable. Kepler may have found over a thousand exoplanets, but new missions are set to dramatically increase that number. The two big upcoming missions are NASA’s TESS, or Transiting Exoplanet Survey Satellite and ESA’s PLATO, or PLAnetary Transits and Oscillations of stars. These will search for worlds that are

transiting some of the brightest stars in the sky. Finding planets around brighter stars is preferred, because it is then easier to detect the atmospheres of these worlds and because the starlight that passes through, the atmospheres is brighter. Other planetfinding projects include NASA’s James Webb Space Telescope (JWST), which will be able to look for planets as well as ESA’s CHEOPS, or CHaracterising ExOPlanet Satellite and the Next-Generation Transit Survey at the European Southern Observatory in Chile. Perhaps one of these will find the first true Earth-like world but how will they know if they have? They can measure transits, which will tell us the size of the world and its orbit, but to determine if a planet is really habitable we need to know about its atmosphere. The JWST will be able to analyse the atmospheres of these worlds, as will another British-led mission called Twinkle, although this will be limited to studying the atmospheres of only the biggest worlds closest to their stars. Still, the technology used in Twinkle could be developed to one day be used on a much bigger space telescope capable of resolving a small, Earth-sized world. If its atmosphere contained lots of oxygen, carbon dioxide and water and if the planet’s colour suggested there could be plant-life, then that would be a strong sign that we would have found another world like Earth. It would be our twin, but separated by dozens or hundreds of light years.

© NASA; NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring; Adrian Mann; Alamy; ESO; Maciej Rebisz

The habitable zone can be found much closer in relatively cool stars such as red dwarfs, which glow at temperatures of around 3,700ºC (6,692ºF).

The search for new Earth

Planetary detection

How can we tell if we’ve found a planet? There are two ways: the radial velocity method and transit method

The star’s light spectrum The star’s light spectrum changes as the star moves toward and away from Earth.

The radial velocity method

Moving toward

When the star moves toward Earth, the light waves it emits are squashed up and we see spectral lines in the blue end of the spectrum. We say that the light we see is blueshifted.

A world’s tug on its star causes a change in a star’s light spectrum Moving away

When a star moves away from us observers on Earth, its light waves are stretched out and we can then see spectral lines in the red end of the star’s light spectrum. We say that the light is redshifted.

Key Planet

Centre of mass

The transit method

Star

The light curve

A dip in a star’s light gives away the presence of an alien world

A light curve is a graph showing the light intensity of a star and thus the light it emits over time.

Out of sight

A dip in brightness

When the planet isn’t travelling across the face of its star, it appears out of sight according to observers on Earth, since no light is blocked out. Brightness

When the exoplanet moves in front of its star it blocks out a portion of light, therefore causing a trough in the star’s light curve.

Time

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e h t d n ehi uld b e c ien that co c s e Th drives tars warp s to the s take u

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Interstellar space travel To date, mankind has managed to send just one object beyond the boundary of our own Solar System. Voyager 1 received gravity assists from both Jupiter and Saturn that boosted its speed to over 61,000 kilometres (38,000 miles) per hour, but it still took 35 years to spiral outwards into interstellar space, 20 billion kilometres (12 billion miles) away. At this speed, Voyager 1 would take another 75,000 years to reach our nearest star, Proxima Centauri. That’s because 61,000 kilometres (38,000 miles) per hour is actually very slow. It’s just 0.005 per cent of the ultimate speed limit for the universe: the speed of light. If you drove your car at the same fraction of the motorway speed limit, you would be travelling ten times slower than a snail. Clearly, we are never going to explore beyond our own Solar System so long as we continue travelling at the speed of our current probes. Even at the speed of light, the universe is still far too massive for us to comfortably explore. It would take more than 100,000 years to cross our galaxy, 2.5 million years to reach the next one, and 45 billion years to reach the edge of the known universe. What we need is some way to travel faster than the speed of light. The problem is that Einstein said this is impossible. Here’s the reason: Einstein's law of special relativity says that the speed of light (referred to by the letter 'c') is always constant, no matter where you are in the universe or how fast you are moving. If you shine a torch out of the front window of a spaceship that is travelling at half the speed of light (0.5c), that beam travels away from you at 1c. An observer, however, hovering in space as you zoom past would also see the beam travelling forward at the speed of light, not 1.5c as you might expect. And if you shine it out of the rear window, both of you will still see the beam travelling at 1c. This is because relative velocities don’t just add together in a simple way. It only seems that way to us on Earth because it’s an approximation that works at low speeds. The faster you go, the less accurate this approximation is, but the difference is only really appreciable once you go faster than about ten per cent of the speed of light (0.1c). As a rocket fires its thrusters, it gets faster, but the amount its speed increases by for each second of thrust is less each time. The rocket could accelerate forever and still never reach the speed of light. This is why physicists say that it would take infinite energy to reach the speed of light – infinity is another way of saying ‘never’. If you can’t reach the speed of light, it follows that you can’t ever go faster than it. This is true for any object that has mass. Suppose we give up on exploring the universe, or even the galaxy. What if we simply settle for just travelling close to the speed of light without actually exceeding it? There are at least 50 stars within 16 light years of Earth, which would let us send a probe there and beam back the data in the same amount of time that the Voyager missions have been running. If you accelerate your probe at a constant 1G (a unit of acceleration that roughly equals ten metres [33 feet] per second squared) for two years, it would be travelling at 97 per cent of the speed of light by the end. That certainly sounds manageable, until you

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Exploration

The father of the warp drive

The Helix Nebula is one of the closest to Earth, but even travelling at light speed, it would take a craft 700 years to reach it. There has to be another way

Dr Miguel Alcubierre tells us about his 1994 paper that covered warp drives and bubbles in space-time Does general relativity permit warp bubbles for warp-drive technology? Warp bubbles are theoretically possible in the sense that the required geometry of space-time is easy to write down. However, they are certainly not solutions in a strict sense. What are the biggest obstacles to creating one? 1: The warp drive would require ‘exotic matter’, with negative-energy densities (antigravity) that – as far as we know – do not exist. It would also require some very weird distributions of momentum and stresses. 2: Even if you get your hands on negative energy and manage to manipulate it, you would need star-sized amounts of it. 3: At super-luminal speeds, the front of the warp bubble is disconnected from the centre. This means that a spaceship sitting in the centre of the bubble has no way of placing the required matter and energy at the front of the bubble. As a superluminal warp bubble cannot be created from within, it would have to be set up in advance from the outside. What happens to the ship if the warp bubble collides with an object while in motion? It depends on the details of the geometry. Of course, hitting anything at a high speed is always very dangerous. Are there other risks with manipulating spacetime directly? These are questions that can’t be answered without knowledge of the properties of the negative energy, which might not even exist. It’s like asking the Ancient Greek philosopher Democritus if you could use his atomic theory to build a bomb.

consider the logistics of firing an engine for that long. The Saturn V rocket used for the Apollo missions, for example, fired its engines for less than 20 minutes total at an average acceleration of about 1.5G. In order to achieve even this short period of acceleration, the weight of the discarded stages and fuel was 60 times the weight of the spacecraft that it propelled to the Moon. To accelerate a rocket continuously for two years, it would need a lot more fuel, but that fuel would need to be accelerated as well, which would require even more fuel and so on. This runaway cycle gets out of hand very quickly indeed. In fact, even if you only wanted to accelerate your space probe to about 0.5 per cent of the speed of light, so that it could reach Proxima Centauri in 850 years, a chemical rocket would need more hydrogen fuel than there is in the entire universe!

You could improve efficiency by switching to nuclear rockets that use fission or fusion to propel your ship with superheated streams of gas. Or, for the ultimate efficiency, you could use matter-antimatter conversion. This might drop the total amount of propellant you'd need to about ten railway tankers' full. Yet if you want the probe to slow down at the other end, you’d need to bring ten railway tankers' worth of propellant to your destination, which would increase the amount of propellant you’d need to get it there to about a thousand supertanker ships' worth of antimatter; a substance that is incredibly difficult to produce. It would take scientists at CERN an entire year to create just a billionth of a gram! It’s possible that in the future we may be able to do away with the need to carry propellant on the spaceship at all. In August this year, a research team at NASA tested a device that appears to produce thrust

Journey to Proxima Centauri World land speed record: 0.34km/s (0.2mi/s) Journey time: 3.7 million years

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SR-71 Blackbird: 0.98km/s (0.6mi/s) Journey time: 1.3 million years

Voyager 1: 17km/s (10.6mi/s) Journey time: 75,000 years

Interstellar space travel

The dangers of warp travel Even if we manage to build a warp drive, would we dare turn it on?

RADIATION Researchers at the University of Sydney in Australia have calculated that particles and radiation could be caught up in the bow wave of a warp bubble as it travels. When the ship decelerates, the accumulated particles would be released in a devastating burst that would destroy anything in the path of the ship.

COLLISIONS The physics of warp bubbles aren’t well enough understood yet to know exactly what would happen if your course takes you through the path of a planet or star. Would it be brushed aside? Would you pass harmlessly though it? Or would you be instantly vaporised? If you fly inside the event horizon of a black hole, could you escape?

NEGATIVE ENERGY

BLACK HOLES

VIOLATING CAUSALITY

What are the properties of negative energy? How would you store it? What happens if your negative-energy battery short-circuits? Whatever the details of the ensuing catastrophe, the numbers involved are likely to be so big that it could destroy the Solar System, never mind the spaceship.

Even if the negative energy doesn’t explode, distorting space-time so heavily could easily create a singularity, where space-time curves in on itself completely – in other words a black hole. Even if the spaceship itself escapes inside its own warp bubble, the consequences for those left behind would be disastrous.

In certain circumstances, travelling faster than the speed of light can enable you to travel back in time. If the universe doesn’t somehow prevent this, you could create all sorts of mind-bending paradoxes, such as going back and killing the inventor of the warp drive, or your very own grandparents.

“It's possible that in the future we may be able to do away with the need to carry propellent on the spaceship at all” out of nowhere by bouncing microwave beams inside a closed chamber. If – and it’s a big if – the results aren’t due to experimental error, this device, known as the Cannae drive would appear to break a fundamental law of physics. A less speculative, propellantless propulsion system would be to use a light sail that catches a stream of photons fired from a highly-focused laser on Earth. Whichever way you do it, you still have to deliver enough kinetic energy to the spacecraft to increase its speed and even without the effort of accelerating the mass of the propellant, the energy requirement is enormous.

NASA’s Glenn Research Center has estimated that sending something the size of the Space Shuttle on a 50-year one-way trip to our nearest star would need 70 million trillion Joules of energy. This is equivalent to diverting the entire electricity-generating capacity of the UK full-time for all of those 50 years. However you do the sums, conventional propulsion techniques just aren’t powerful enough to explore the stars. Yet there might be a loophole. Special relativity says that no object can be accelerated to the speed of light, but it doesn’t say anything about how fast space itself can move. Think of an airport travelator. You

Proxima Centauri: 4.2ly from Earth

Light-speed spacecraft Journey time: 4.2 years

walk along it at your normal pace, but because the floor is moving as well, your total speed seems much faster to someone walking beside the travelator. We aren’t adding the velocities of two objects moving on the ground; instead we are moving the very ground we walk on. Einstein’s theory of general relativity showed that the three dimensions of space itself can be stretched and curved. It’s a bit like a map. Maps can be flat and show places according to their positions along the width and length of the paper, or they can be globes that show them using latitude and longitude. The map is two-dimensional in both cases, but with a globe, those dimensions are curved into a third dimension. Over short distances, if the curvature is quite small, the surface of the globe will still seem flat. But if you stretch it more dramatically, some interesting things happen. Suppose our universe globe is painted on a balloon and you push your fingers in from opposite sides so that the surface gets more and more indented. Eventually, your fingers are touching, with just the skin of the balloon between them. If you could punch through this skin without bursting the balloon, you could hop from one side of the universe to the other without travelling all the way around the outside. This form of distortion is called a wormhole. One common objection that is raised against wormholes as a practical form of travel is that you need to position the far end where you want to go before you can travel there. If the ends of the wormhole are some kind of Stargate device, you would need to physically transport one of them there at sub-light speeds first. However, the amazing properties of wormholes could come to your rescue. A spacecraft carrying a Stargate doesn’t need to bring its own fuel because you can just pipe fuel through

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Exploration

Warp drive starship

Dr Harold White's warp travel spacecraft of the far future Space efficient

The larger the warp bubble, the more energy it will inevitably need, so it is important to utilise the space inside it as efficiently as possible to store as much energy as it can.

Solar panels

When the ship isn’t travelling at warp speed, it will still use old-fashioned solar power in order to preserve its precious supply of antimatter fuel for the warp drive.

Impulse drive

There may be restrictions on using warp drive at low speeds or when near planets, so traditional reaction jets will still be needed when it comes to manoeuvring.

Crew section

Warp rings

The energy needed to create the warp bubble is greater if the boundary of the bubble is sharp. Using thicker rings, Dr White thinks we could produce a thicker warp field.

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In the middle of the warp bubble, spacetime is perfectly flat, so the crew will experience absolutely no acceleration as they make their way between the stars.

International co-operation

The resources needed to research, develop and build a warp ship will exceed the budget of any one country, so every nation will need to join in.

Interstellar space travel

Fuel tanks

A warp drive may need antimatter to supply enough energy. This will have to be stored inside electromagneticconfinement tanks to stop it from touching the sides of the ship.

Communication array The warp bubble is disconnected from the rest of the universe, so the crew will only be able to communicate with Earth when the warp drive is turned off.

the wormhole and have it delivered instantly, regardless of how far the ship has travelled. This doesn’t violate the law of conservation of energy, because the extra mass you have supplied to the travelling ship causes the wormhole to shrink. To keep the size of the wormhole constant, you would need to pump extra energy into the device that powers it. According to professor John Cramer of the University of Washington, every kilogram (2.2 pounds) of fuel that you send through the wormhole would need 25 million megawatt-hours of extra power to keep the wormhole open. This is roughly as much electricity as the entire world produces every five weeks, so even if we diverted all our power into the Stargate, we wouldn’t be able to send more than two kilograms (4.4 pounds) of fuel per month. Imagine we have access to enough electricity to be able to pump fuel constantly through the wormhole and allow the spaceship to accelerate close to the speed of light (let’s say 99.995 per cent) and we send it to Tau Ceti, a star 12 light years away. You might assume that it would be about 12 years before the spaceship would arrive and we could use our wormhole, but Einstein showed that time slows down the faster you travel. At 99.995 per cent of the speed of light, time would pass 100 times more slowly. So for the captain of the ship, the 12-year journey would only appear to have taken 44 days. This is only true for time aboard the spaceship of course, but remember that the Stargate it carries is connected through the wormhole to the other end on Earth. Anyone looking through the wormhole would see the same view out of the front window of the spaceship as the captain sees. This means that after just 44 days they would see Tau Ceti loom into view, while Earthbound telescopes would see that the spaceship was only one per cent of the way there! Convenient as this sounds, it raises a much bigger problem with faster-than-light travel. Ian Crawford is professor of Planetary Science and Astrobiology at Birkbeck, University of London. “With a faster-than-light drive, you can contrive situations where you would go backwards in time,” he says. “And that is a big problem. If it's possible to travel faster than light then there must be some higher-order physical law that would prevent you from messing around with causality.” Theoretical physicist Stephen Hawking calls this the chronology protection conjecture. “When space-time gets warped almost enough to allow travel into the past,” he says, “virtual particles can almost become real particles […] And their energy [becomes] very large. This means that the probability of these [alternative] histories is very low [...] making the world safe for historians.” So wormholes might stretch space-time to breaking point, but there are other ways to warp

it that might allow us to travel faster than light, without travelling into the past. In 1994, Mexican physicist Miguel Alcubierre published a solution for the equations of general relativity that showed a way to create a bubble of distorted space-time around an object. By contracting space-time in front of a spaceship and expanding it behind, you could create a ripple in space-time that could roll across the universe, carrying the ship with it. The patch of space-time immediately surrounding the ship would be flat so the ship wouldn’t actually be moving in the traditional sense, but it would be carried on the ripple of curved space-time, like a surfer riding a wave. We don’t know how to make wormholes or warp bubbles yet. All we know is that general relativity doesn’t forbid them. However, the distortions that you need to travel faster than light involve bending space-time in the opposite direction to the way that gravity bends it. That suggests we would need negative matter or energy to achieve it. As exotic as that sounds, it’s possible that negative energy may actually exist. If you put two metal plates in a vacuum chamber and hold them about ten nanometres apart, they will be pulled together by something called the Casimir effect. This is thought to be because even a total vacuum has some energy and the space between the plates is too small for all the possible wavelengths of this vacuum energy to fit in it. So the gap between the plates somehow has less energy that the ordinary vacuum and they are pushed together by vacuum energy on the outside surfaces. Since the energy of the vacuum is zero, by definition, this means that there is negative energy between the plates. Miguel Alcubierre dismisses this form of negative energy. “Even if it exists, we have absolutely no idea how to use it for anything useful, let alone a warp drive.” Professor Crawford raises an even more fundamental objection. “The Casimir effect arises out of the quantum vacuum […] We’re trying to use quantum theory to generate negative energy as a way of keeping wormholes open, which are a prediction of general relativity, and we know that we can’t marry quantum theory to general relativity yet.” In the same way that the theories of electricity and magnetism were eventually realised to be different aspects of the same thing (electromagnetism), theoretical physicists have been working for decades to produce a theory of quantum gravity. “When we do have a theory that reconciles general relativity and quantum theory, we don’t know whether these loopholes will still be there,” warns Crawford. “They might disappear once we have a more complete theory of gravity. On the other hand, a more complete theory may tell us that it's easier than we thought.” There are an estimated 10,000 times more stars in the night sky than there are grains of sand on Earth. If one per cent of them have Earth-like planets around them and one per cent of those have life and one per cent of those have intelligent civilisations,

“With a faster-than-light drive, you can contrive situations where you would go backwards in time” Ian Crawford 55

Exploration that’s still about 10 million billion civilisations in the observable universe. If warp travel is possible, it seems even more extraordinary that we haven’t been visited by any of them yet. This is known as the Fermi paradox, after physicist Enrico Fermi. One possible solution, known as the Zoo hypothesis, is that some sort of Prime Directive exists whereby spacefaring aliens all agree not to interfere with less advanced species. “The problem with the Zoo hypothesis,” says Crawford, “is that it would require all of these aliens to agree to the same set of rules for the zoo.” According to Crawford, the only way this might be plausible is if warp travel is possible. “In the context of near-instantaneous travel and communication, then it becomes possible to imagine galactic political structures – Empires and Federations – that might be able to impose quarantines on planets where intelligence has just emerged. Yet it also makes it much easier to travel interstellar distances, so in fact there is a balance between galactic-scale political institutions that can force Prime Directives and the fact that there will be many more intelligent beings flying around the galaxy.” NASA’s official stance on warp travel places it firmly in the realm of speculation. This doesn’t mean they are ignoring it completely though. Dr Harold White at NASA’s Johnson Space Center in Houston, Texas, is working on a modified version of a device called a Michelson interferometer, which will use a ring of high-voltage capacitors to induce a small warp field. If it works, it should be possible to detect it by shining a laser through the field and measuring its speed. Results so far have been inconclusive, but professor Crawford applauds the effort. “Because the physics is still just not understood, most professional physicists won’t engage with it. It’s just considered too speculative. So it’s hats off to people like Alcubierre and Harold White and others who are sticking their heads above the parapet and pursuing the research seriously. I do think that’s worth encouraging.” Ultimately, even if warp drives are possible, professor Crawford believes there’s no guarantee that they would be any easier to build or less expensive to power than sub-light spaceships. “We don’t know what’s involved in building a faster-than-light probe, but we know we aren’t going to wake up one morning and find that we’ve got it for Christmas. It’s going to have to be developed, and developed from physical principles we don’t understand. Interstellar space travel is really a matter of learning to walk before you can run. We have to gradually build up an industrial infrastructure within our own back yard, moving out into the Solar System, where eventually we will develop the expertise and the economic wealth that will enable us to invest some fraction of that in interstellar exploration.” Warp-drive research might seem like the philosophers’ stone, the substance that could turn other metals into gold. The quest for this shortcut to riches was one that obsessed alchemists for centuries and, of course, they never found it. However, their search laid the foundations for the understanding of chemistry that we have today, which eventually gave us electricity, nuclear power and rocket fuel. So perhaps it wasn’t entirely a waste of effort after all.

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Warp-drive tourism Unless warp drive turns out to give us infinite speed, journeys beyond our galaxy are probably still out of reach. If we could travel at 1,000 times the speed of light, however, some very interesting places in the Milky Way would suddenly become accessible. ly = Light years

M80

Distance: 32,600ly On the furthest side of the Milky Way to Earth, this globular star cluster is packed with hot blue straggler stars, which seem out of place and might have been captured by M80's gravity from another part of the galaxy.

High-velocity gas clouds

Distance: 14,000ly Lying above the plane of the galactic disk, these clouds constantly bring new gas into the galaxy to allow it to keep producing new stars. We still don’t know where the clouds come from though, so it would be very useful to be able to visit them.

Interstellar space travel Arches cluster

Blue stragglers

Distance: 26,000ly Blue stragglers are a rare and puzzling sort of star that may form when binary stars merge. This reinvigorates their nuclear fusion, making them seem younger than the other stars in their neighbourhood.

Distance: 25,000ly This is the most densely packed group of stars in the galaxy. This cluster is only about two million years old and contains some mysterious magnetic fields that trap arches of high-energy particles.

Galactic core

Distance: 26,000ly The central 30,000ly region of the galaxy is a swirling mass of hot, ionised gas and massive stars. Dust clouds obscure our view of it from Earth in the visible wavelengths of light. This image was taken with the Hubble Space Telescope’s nearinfrared camera.

Kepler-186f

Tau Ceti e

Ancient white dwarfs

Distance: 7,200ly The M4 globular cluster in the constellation of Scorpius contains some of the oldest stars in the galaxy. These stars are 13 billion years old and formed quite early on in the life of the universe. They are now almost burned out and quite cool and faint.

Distance: 12ly The existence of this exoplanet hasn’t been conclusively proved yet, but it could be one of the nearest Earth-like planets to our own. With a warp drive, we could quite easily send a probe to take photos of its surface conditions to check.

Distance: 500ly Currently one of the best candidates for the most Earthlike planet award, Kepler-186f is just ten per cent larger than Earth, with a rocky surface and a good chance for surface water. Its star is much fainter though; midday on this planet would be just like an hour before sunset on Earth.

Proxima Centauri

Distance: 4.2ly As our nearest stellar neighbour, we should certainly visit to see if it has planets. Proxima Centauri is prone to sudden and dramatic flare-ups though, so it probably doesn’t have any native life.

Sedna

Distance: 12 Light hours The furthest planetoid in our Solar System is puzzling. Its slow rotation suggests it should have a Moon, but Hubble images don’t show one. A quick trip with a warp drive could solve the mystery.

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Solar System

From the Kármán line to beyond the orbit of Pluto 60 Birth of the Solar System Find out how our Solar System formed

70 This is Pluto

The dwarf planet with a huge heart and the biggest discovery of the 21st Century

78 Exploring Mars

Set foot on the red earth of Mars

82 Traversing Callisto

Puzzle over the mysteries of Jupiter's icy outermost moon

86 Space volcanoes

Discover how volcanoes have shaped the celestial bodies of our Solar System

“Further back in history there is evidence that Mars was rich in surface water”

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Exploring Mars 58

60

Birth of the Solar System

70

The biggest discovery of the 21st Century

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Traversing Callisto

86

Space volcanoes

©NASA, New Horizons, Mark A. Garlick

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60

Birth of the Solar System

Birth of the

SOLAR SYSTEM How did our Solar System form? Until recently, astronomers thought they knew. But now, new research is turning many of the old ideas on their heads

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Solar System Around 4.5 billion years ago, our Sun and all the other objects that orbit around it were born from an enormous cloud of interstellar gas and dust, similar to the glowing emission nebulae we see scattered across today’s night sky. Astronomers have understood this basic picture of the birth of the Solar System for a long time, but the details of just how the process happened have only become clear much more recently – and now new theories, discoveries and computer models are showing that the story is still far from complete. Today, it seems that not only did the planets form in a far more sudden and dynamic way than previously suspected, but also that the young Solar System was rather different from that we know now. The so-called ‘nebular hypothesis’ – the idea that our Solar System arose from a collapsing cloud of gas and dust – has a long history. As early as 1734, Swedish philosopher Emanuel Swedenborg suggested that the planets were born from clouds of material ejected by the Sun, while in 1755 the German thinker Immanuel Kant suggested that both the Sun and planets formed alongside each other from a more extensive cloud collapsing under its own gravity. In 1796, French mathematician Pierre-Simon Laplace produced a more detailed version of Kant’s theory, explaining how the Solar System formed from an initially shapeless cloud. Collisions within the cloud caused it to flatten out into a spinning disc, while the concentration of mass towards the centre caused it to spin faster (just as a pirouetting ice skater spins faster when they pull their arms inwards).

In the broad strokes described above, Laplace’s model is now known to be more or less correct, but he certainly got some details wrong, and left some crucial questions unanswered – just how and why did the planets arise from the nebula? And why didn’t the Sun, concentrating more than 99 per cent of the Solar System’s mass at the very centre of the system, spin much faster than it does? Solutions to these problems would not come until the late 20th century, and some of them are still causing doubts even today. Much of what we know about the birth of our Solar System comes from observing other star systems going through the same process today. Stars are born in and around huge glowing clouds of gas and dust, tens of light years across, called emission nebulae (well known examples include the Orion Nebula, and the Lagoon Nebula in Sagittarius). The nebulae glow in a similar way to a neon lamp, energised by radiation from the hottest, brightest and most massive stars within them, and remain active for perhaps a few million years, during which time they may give rise to hundreds of stars forming a loose star cluster. Since the brilliant, massive stars age and die rapidly, it’s only the more sedate, lowermass stars like our own Sun that outlive both the nebula and the slow disintegration of the star cluster. Star birth nebulae develop from the vast amounts of normally unseen, dark gas and dust that forms the skeleton of our Milky Way galaxy, and subside as the fierce radiation from their most massive stars literally blows them apart. The initial collapse that kick-starts formation can be triggered in several

“Much of what we know about the birth of our Solar System comes from observing other star systems” How stars are formed

Disturbed nebula

The birth of a star begins when a cloud of interstellar gas and dust passes through a galactic density wave, or is compressed by shock from a nearby supernova or tides from a passing star.

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Slow collapse

Denser regions within the nebula start to collapse under their own gravity. As mass concentrates towards their centres, they begin to spin more rapidly, and their cores grow hotter.

ways – for instance by a shockwave from a nearby exploding supernova, or by tides raised during close encounters with other stars. However, the biggest waves of star birth are triggered when material orbiting in our galaxy’s flattened outer disc drift through a spiral-shaped region of compression that extends from the galactic hub and gives rise to our galaxy’s characteristic shape. Inside the nebula, stars are incubated in huge opaque pillars of gas and dust. As these pillars are eroded by outside radiation from massive stars that have already formed, they break apart into isolated dark globules whose internal gravity is strong enough to hold them together – the seeds of individual solar systems. Gas falling towards the very centre of the globule becomes concentrated, growing hotter and denser until eventually conditions are right for nuclear fusion, the process that powers the stars, to begin. As the star begins to generate energy of its own, its collapse stabilises, leaving an unpredictable stellar newborn surrounded by a vast disc of gas and dust that will go on to form its solar system. But how? That’s where things get really interesting… The first person to put Laplace’s hypothesis on a sound theoretical footing was Soviet astronomer Viktor Safronov, whose work was first translated from Russian around 1972. Safronov’s modified ‘solar nebular disk model’ allowed the Solar System to form from much less material, helping to resolve the problem of the Sun’s slow spin. What was more, Safronov provided a basic mechanism for building planets out of primordial dust grains, known as ‘collisional accretion’. This simple mechanism involves small particles colliding and sticking to each other one at a time, eventually growing into objects that were large enough to exert gravitational pull and drag in more material from their surroundings. This produced

Flattening disc

Collisions between randomly moving gas clouds and dust particles tend to flatten out their motions into a narrow plane, creating a disc that spins ever more rapidly.

Birth of the Solar System objects called planetesimals, the largest of which might have been about the size of the dwarf planet Pluto. A final series of collisions between these small worlds created the rocky planets close to the Sun, and the cores of the giant planets further from the Sun. The difference between the two main types of planet is then explained by the existence of a ‘snow line’ in the early Solar System, around the location of the present-day asteroid belt. Sunward of this, it was too warm for frozen water or other chemical ices to persist – only rocky material with high melting points survived. Beyond the snow line, however, huge amounts of ice and gas persisted for long enough to be swept up by the giant planets. It all sounds simple enough, and has been widely accepted for the best part of four decades. But now that seems to be changing. “There’s been the beginning of a paradigm shift away from the twobody build-up that Safronov modelled,” says Dr Hal Levison of the Southwest Research Institute (SwRI) in Boulder, Colorado. “The idea of things growing by collisions hasn’t really changed but over the last five years or so, new theories invoking the idea of pebbles [are] coming to the fore. We’ve really only now got to the stage where we can discuss these ideas in any great detail.” The new approach stems from a long-standing problem: “The big question is how you get the first macroscopic objects in the Solar System – things that are bigger than, say, your fist,” explains Levison. “Safronov’s idea was that you just did that through collisions, but people have always recognised there’s a problem we call the metre barrier.” “You only have to look under your bed to see plenty of evidence that when small things hit one another, they can stick together, making these dust bunny clumps that are held together by electrostatic forces [weak attraction between innate static electric charges]. And if you look at objects bigger than, say

Birth of a protostar

As more and more material falls into the core of the nebula, it starts to radiate substantial infrared radiation that pushes back against the tendency to collapse. The core of the nebula is now a protostar.

Known as N90, this emission nebula in the Small Magellanic Cloud shows many features associated with the birth of stars, with a central cluster dominated by heavyweight stars, and stalactite-like opaque pillars where star birth is still continuing

Ignition!

Finally, conditions at the heart of the protostar become hot and dense enough for nuclear fusion to begin converting hydrogen into helium. The star now begins to shine properly, but goes through violent fluctuations before it stabilises.

Bipolar outflow

Gas continues to fall onto the infant star, accumulating around its equator but being flung off at its poles in jets known as bipolar outflow. Radiation pressure starts to drive gas out of the surviving nebula.

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The birth of the planets Our Solar System was cooked up in a swirling cloud of gas and dust

8Planetary migrations 9The Solar System today

1 Shapeless cloud

The neat, near-circular orbits of today’s planets are an inevitable result of their formation from the merging of many objects in a disc around the Sun – while many solar systems around other stars seem to have planets in much wilder orbits, this is probably a result of later gravitational interactions and phases of planetary migration like the ones that once shaped our own Solar System.

During one or more phases of planetary migration, the giant planets of the outer Solar System change their configurations and locations, moving back and forth through a host of smaller bodies (asteroids, small comets formed between the giant planets, or ice dwarfs orbiting beyond). The havoc they wreak ultimately gives rise to the modern asteroid belt, Kuiper belt and Oort cloud, though the latter may also include comets captured from other stars born alongside the Sun.

About 4.5 billion years ago, the raw materials of the Solar System lay in a shapeless cloud of gas and dust. Its dominant components were hydrogen and helium, but it was also enriched with elements created by previous generations of stars, and scattered through the so-called interstellar medium. These included carbon, oxygen and nitrogen, as well as dust grains (often carbon-based) up to one micrometre (0.001mm or 4x10-5in) across.

2 Collapse begins

The trigger event for the formation of an emission nebula typically produces condensation in several regions of the cloud that happen to have higher densities. Each may give rise to a whole group of stars – once the first stellar heavyweights have begun to shine, their radiation helps energise the nebula, and also sculpts its shape, dictating where the younger generations of stars will form. However, by blowing material out of the nebula, these early giants also stunt the growth of their siblings.

Individual systems 3 “The old idea of getting to Mars-sized

objects by banging Moon-sized things together could be wrong”

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A single globule of collapsing gas and dust may give rise to a single star of a multiple star system at its centre. As material falls inward, collisions between gas clouds and particles tend to cancel out movements in opposing directions, while an effect known as the conservation of angular momentum causes the cloud’s central regions to spin faster as most of the mass concentrates there.

Birth of the Solar System

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Growing pains

As the new protoplanets continue to orbit the Sun, their gravity draws in huge numbers of remaining pebbles and they grow rapidly. In the inner Solar System, where material is limited, they reach the size of Mars – Earth and Venus subsequently form from collisions between several such worlds. In the outer Solar System copious ice allows them to reach roughly the size of Uranus. Two of these worlds then grow further by absorbing huge amounts of gas to create Jupiter and Saturn.

6Planets from pebbles

Within the nebula, the seeds of planets start to form – according to the latest theories, these are huge drifts of pebble-like particles herded together by turbulence in the surrounding gas. Rather like cyclists in a road race, they cluster into huge streams to reduce the headwinds they encounter. Eventually, these pebble clouds grow massive enough to collapse under their own gravity, forming protoplanets up to 2,000km (1,240mi) across.

5Protoplanetary system

4Flattening disc

The end result of the cloud’s collapse is a spinning disc with an orientation derived from the slow random rotation of the original globule. Dust and ice particles tend to concentrate more efficiently around the central plane of this disc, while gas forms a looser halo, and continues to fall in towards the central regions until conditions there become extreme enough to create one or more protostars.

A few million years after the initial cloud began to collapse, nuclear fusion has ignited in the central star, and most of the excess gas has disappeared – either dragged in by the Sun’s gravity, ejected in bipolar jets along the system’s axis of rotation. What remains lies closer to the plane of the Solar System, and it, too, is gradually being driven away by the Sun’s radiation.

a few kilometres across, gravity can hold things together. But if you’re looking at something, say, the size of a boulder, then it’s hard to imagine what makes those things stick.” Fortunately about ten years ago, researchers including Andrew Youdin (University of Arizona) and Anders Johansen (now at Sweden’s Lund University) came up with an ingenious way around the problem. “What they’ve shown is that as dust grains settle into the central plane of the protoplanetary disc, that causes a kind of turbulence that concentrates the pebbles into large clumps,” continues Levison. “And eventually these clumps can become gravitationally unstable and collapse to form really big objects. This model predicts that you go directly from things the size of your fingernail to hundred-kilometre [62-mile]-sized objects, in just one orbit around the Sun.” Over the past few years, as various teams including Levison’s group at SwRI have worked on the theory, they’ve found that the clumping process is even more effective than they first thought: “We’re talking about objects up to the size of Pluto forming this way, out of pebbles.” And that’s just the first stage: “Once you get up to that size, you get a body that can grow very effectively by eating the surrounding pebbles, pulling stuff in with its gravity and maybe growing into something the size of Mars. So the old idea of getting to Marssized objects by banging a lot of Moon-sized things together could be wrong.” This new theory could help solve several outstanding problems with the Solar System, such as the relative ages of the Earth and Mars. “Mars seems to have formed about 2 to 4 million years after the Sun formed, while Earth formed about 100 million years later,” explains Levison. The theory, then, is that Mars was entirely formed by the two stages of the pebble accretion process, while Earth still had to go through a final phase of Safronovstyle planet-scale collisions in order to reach its present size. “Pebbles can also help to explain how the giant planets formed as quickly as they did,” Levison enthuses. “Most astronomers accept the ‘core accretion’ model for the giant planets, where you start out with four objects the size of Uranus and Neptune, and two of those then accumulate gas and grow to become Jupiter and Saturn. But the problem is that you need to build those cores before all the gas goes away. In the traditional Safronov model, that’s hard to do, but again this new pebble accretion model can do it really quickly.” The difference in scale between the Mars-sized rocky objects and the much larger giant-planet cores, meanwhile, is still to do with availability of raw material, with copious icy pebbles surviving only in the outer Solar System. But there’s one other big problem in matching the Solar System we know today with the original solar nebula – the positions of the planets, and in particular the cold worlds of the outer Solar System. Today, Uranus orbits at a distance of 2.9 billion kilometres (1.8 billion miles) from the Sun, and Neptune at 4.5 billion kilometres (2.8 billion miles). Beyond Neptune, the Kuiper belt of small, icy worlds (including Pluto and Eris) extends to

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Solar System

“The new pebble accretion model can help to explain how the giant planets formed as quickly as they did” Dr Hal Levison more than twice that distance, and then there’s the Oort cloud – a vast spherical halo of icy comets that extends to around 15 trillion kilometres (9.3 trillion miles). The solar nebula, meanwhile, would have been most concentrated around the present orbit of Jupiter, and trailed off from there – while computer models suggest Uranus and Neptune could not have grown to their present size unless they were closer to Jupiter and Saturn. All of which brings us to the work for which Levison is perhaps best known – his contribution to the so-called ‘Nice model’ of planetary migration. This explains the current configuration of the Solar System as the result of the dramatic shifting of the planets that happened around 500 million years after its formation. “The Nice model goes back some ten years now,” recalls Levison. “It postulated a very compact configuration for the outer planets when they formed, with Jupiter and Saturn, probably Neptune next, and then Uranus all orbiting in the outer Solar System, and beyond that, a disc of material with the mass of about 20 Earths. The biggest objects inside that disc would have been about the size of Pluto.” In the Nice scenario, all four giant planets formed within the present-day orbit of Uranus, with the Kuiper belt extending to about twice that diameter,

Comets are icy remnants left over from the early days of the Solar System, and may have a lot to tell us about its raw materials and early dynamics. However, Hal Levison has argued that the distant Oort cloud could also have been enriched by comets swept up from the Sun’s siblings in its birth cluster

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yet still inside the current orbit of Neptune. But this arrangement was doomed to instability, and around 4 billion years ago, Uranus and Neptune began a series of close encounters that disrupted their orbits and put them onto new paths around the Sun. Now, for various reasons, the orbits of Uranus and Neptune became unstable – they started having encounters with each other that threw them into orbits going all over the Solar System, and then having encounters with Jupiter and Saturn. “Before too long, they began having encounters with Jupiter and Saturn,” continues Levison, “and the gravity of these giant planets threw them out into the disc of Kuiper belt objects. Gravitational interactions between Uranus, Neptune and these objects circularised the orbits of the giant planets, and ejected most of the smaller objects either out into the present-day Kuiper belt, or in towards the Sun. It was a very violent, short-lived event lasting just a few tens of million of years, and we think we see the evidence for it on the Moon, where the impact rate went up around 4 billion years ago in an event called the Late Heavy Bombardment.” Perhaps unsurprisingly, the Nice model has been tweaked a little in the decade since its first publication: “The exact mechanism that causes the instability has changed a bit, and there’s work by

Birth of the Solar System Planetary systems caught in the act of formation have a lot to teach us about the origins of our own Solar System. This Hubble Space Telescope image shows a ring of protoplanetary dust with a possible planet moving through it around the young star Fomalhaut, some 25 light years from Earth

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xxxxxxxxxxxxx Solar System

“In the Nice scenario, all four giant planets formed within the present-day orbit of Uranus”

Japan’s Hayabusa 2 probe plans to land on a near-Earth asteroid that originated in the main asteroid belt, bringing back samples that could tell us whether water from asteroids contributed to Earth’s oceans

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Birth of the Solar System

Types of planets

Ice giant

Metallic core

Heavy elements such as iron and nickel sank towards the centre of the newly formed planets, where they formed molten cores. Over time, the smaller ones have begun to solidify.

Rocky core?

The ice giants probably have solid rocky cores – while they formed from drifts of rocky and icy pebbles, gravity and pressure will have long ago separated them into distinct layers.

Rocky planet Cold atmosphere

Slushy interior

Unlike the gas giants, the ice giants lack a deep envelope of hydrogen and helium. These light elements still dominate their atmosphere, however, while their distinctive colour comes from methane.

The bulk of an ice giant is a deep ‘mantle’ layer of chemical ices (substances with fairly low melting points). These include water ice, ammonia and methane.

Mysterious core

The cores of the gas giants are poorly understood, though our knowledge should improve when the Juno probe arrives at Jupiter in 2016. If new theories are correct, they should show some resemblance to the nearby ice giants.

Inner ocean

The interiors of Jupiter and Saturn are largely composed of liquid molecular hydrogen, breaking down into liquid metallic hydrogen (an electrically conductive sea of individual atoms) at great depths.

Gas giant Outer atmosphere

The rocky planets of the inner Solar System formed from high-melting point ‘refractory’ materials that could survive close to the young Sun. This is mirrored in their composition today.

Mantle

Heat escaping from the core of a rocky planet causes the semi-molten rocks of the mantle to churn very slowly, carrying heat towards the surface and creating geological activity.

David Nesvorny, here at SwRI, arguing that you’re more likely to end up producing the Solar System that we see if there were initially three ice giants instead of two, and we lost one during the process.” Mention of the Moon’s late bombardment raises an interesting question – could some form of planetary migration also help resolve the long-standing question of where Earth’s water came from? According to current theories, the environment in which the planets formed was a dry one, so the theory that our present-day water arrived later from somewhere else in the Solar System is a popular one. Yet measurements from comet probes such as ESA’s Rosetta shows subtle but important differences from the water found on Earth. “In fact, Jupiter wields too big of a baseball bat for comets to have made much of a contribution to water on Earth,” points out Hal Levison. “Its gravity simply forms too big a barrier between the outer and inner Solar Systems, so at most ten per cent of water on Earth could have come from comets. We’ve known that for some time from dynamics

“Jupiter wields too big of a baseball bat for comets to have made much of a contribution to water on Earth” Dr Hal Levison – we don’t really need the cosmochemical measurements taken by probes like Rosetta to prove that. Instead Earth’s water probably came from objects in the outer asteroid belt, and there’s a separate planetary migration model called the Grand Tack that offers one way to do that, though I think it has some problems.” The Grand Tack is part of the planet formation story itself – it involves Jupiter moving first towards, and then away from the Sun, due to interaction with gas in the solar nebula. In the process, its gravitational influence robbed Mars of the material required to grow into an Earth-sized planet, but later enriched the outer asteroid belt with waterrich bodies that might later have found their way to Earth. If that’s the case, then Japan’s recently

launched Hayabusa 2 probe, which aims to survey a nearby asteroid and return samples to Earth around 2020, could provide more information if it discovers Earth-like water in its target, a small body called 1999 JU3. “The Grand Tack is one way of solving the problem of why Mars has just ten per cent of the mass of Earth and Venus, when most models predict it should be just as massive if not more so, but the pebble accretion work we’re doing may also solve it,” argues Levison. It seems clear, then, that it’s an exciting time for scientists probing the origins of the Solar System – who would have thought, a few short years ago, that so many answers might lie in the realm of seemingly insignificant interplanetary pebbles?

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© NASA; Science Photo Library; Sayo Studio; Tobias Roetsch

Rocky crust

The gas giants grew to enormous sizes by soaking up leftover gas from the solar nebula – today this forms a deep envelope of hydrogen and helium that transforms into liquid under pressure beneath the clouds.

THIS IS

PLUTO Welcome to the dwarf planet with a huge heart, the biggest discovery of the 21st Century

1930

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1994

2005

April 2015

This is Pluto

23 July 2015

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Solar System

What has New Horizons taught us about Pluto? NASA’s nine-year mission to study Pluto moved up a gear in July 2015 when New Horizons began its approach, carrying a battery of spectrometers, visual and infrared cameras to within 12,500 kilometres (7,800 miles) of the mysterious dwarf planet. The atmosphere in mission control must have been tense as New Horizons neared its primary mission objective. On 4 June, with just ten days to go, New Horizons’ systems overloaded and it went silent. A built-in recovery protocol directed the craft to engage its backup computer and call home for help but communications take nine hours to travel from its systems to Earth and back again, so identifying

and fixing the problem was a tense process. A day later, NASA confirmed that New Horizons was healthy once again and, despite the loss of a day’s worth of data, it was in good shape for the upcoming approach to Pluto. The two-hour-and-15-minute flyby was a triumphant success and with more than 50 gigabits of data gathered over all nine days of the close approach, the team must wait for it all to be transmitted back to Earth. For now, New Horizons is sending compressed versions of its observations, and the download of the full dataset won’t be complete until late 2016.

Pluto has a heart

The craft has enough fuel to remain active until 2020, and the team is already lining up a Kuiper Belt flyby for 2019. This extended mission is still pending approval from NASA but could provide an incredible insight into the mysterious objects found in the far reaches of our Solar System. After it completes its active duty, New Horizons will join the Pioneer and Voyager probes on their journeys into deep space. The ashes of Clyde Tombaugh, the man who discovered Pluto, are on board the craft and, as New Horizons continues on its travels, his will become the first human remains ever to leave the Solar System.

What we knew Before New Horizons, our best images of Pluto were still a fuzzy blur, not even the Hubble Space Telescope could improve them much. All we knew was that it was reddish in colour, and that the blotchy patterns on its surface changed over time. What we now know The dwarf planet is much loved, and when New Horizons sped towards its closest approach, many people were delighted when it snapped images revealing that Pluto has a heart. The bright feature, found just above the equator, measures around 1,600km (1,000mi) across.

The bright part of Pluto’s heart could be filled with snow, contrasting with Charon (right)

Frozen nitrogen snows on Pluto

The ‘heart’, or Tombaugh region, named after Pluto’s discoverer

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What we knew Snow is unusual in the Solar System. On Earth, it seems very familiar, but there are only a few other places where any frozen flakes fall – Mars, Jupiter’s moon Io, and Saturn’s moon Titan. What we now know Pluto has an atmosphere of nitrogen, and there is evidence of geological activity beneath its surface – making snow on its surface a possibility. When asked about whether surface features could be snow, New Horizons principal investigator Alan Stern told the media, “it sure looks like it”.

This is Pluto

Mountains bigger than the Rockies cross Pluto’s surface

It’s bigger than we thought What we knew Pluto’s tiny size saw it demoted to dwarf planet in 2006, but until now we weren’t sure of its actual dimensions. Its atmosphere complicates measurements, but it was estimated to span around 2,306km (1,432mi). What we now know According to the latest measurements from New Horizons, Pluto is actually 2,370km (1,472mi) in diameter. An additional 64km (40mi) might not sound like much, but the extra inches make Pluto ever so slightly larger than dwarf planet Eris – which started the planet debate in the first place.

There are huge ice mountains

What we knew It was obvious from the moment of Pluto's discovery that it was going to be cold, but exactly how its frozen surface would look was a mystery. It was expected that Pluto would be flat and lacking any evidence of active geology.

It has a youthful moon

What we now know Pluto is home to jagged mountains, some taller than Canada's Rockies. NASA scientists think that they are made up of water ice, frozen so solid that it has the consistency of stone, covered in a thin layer of methane, carbon monoxide and nitrogen.

The surface is changing

What we knew Pluto is 4.5 billion years old and 5.9 billion km (3.7 billion mi) from the Sun, so we thought it’d be cold and dead. Without any geological activity to reshape the surface, we expected it to be covered in craters. What we now know New Horizons spotted unusual frozen plains on Pluto’s surface. Smooth and uncratered, they were likely formed within the last 100 million years, making this one of the youngest features in the Solar System. It indicates that something is keeping the inside of the dwarf planet warm, we just don’t know how.

Earth, compared to Pluto (above centre) and Charon

The young, relatively smooth plains surprised scientists

Charon’s deep canyon can be seen in shadow on the right of the moon What we knew Pluto’s largest moon, Charon, was only discovered in 1978. At half the size of Pluto, it is sometimes argued that it is a dwarf planet in its own right. Scientists thought its surface might be covered in craters. What we now know Charon has become one of the stars of the mission after NASA revealed It has a system of deep cracks that put the Grand Canyon to shame. It has surprisingly few impact craters, indicating that there is some geological activity below the surface. An enormous, as yet unidentified, dark spot scars its surface.

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Mission control

The team pauses to celebrate as New Horizons returns historic images of Pluto As the short binary message came through from New Horizons on 14 July 2015, the researchers at mission control crowded around to hear. “We are in lock with telemetry with spacecraft,” said operations manager, Alice Bowman. “It looks like we have a good data record.” The room erupted with cheers. “We have a healthy spacecraft. We’ve recorded data from the Pluto system. We are outbound from Pluto,” Bowman finished, to another round of applause. After a tense 21-hour wait, the New Horizons team had gathered anxiously at mission control, waiting for this critical moment. During its historic flyby,

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New Horizons had turned away from Earth to focus on gathering as much scientific data as possible. This meant that it was radio silent for almost a day. The routine had been planned and rehearsed in advance, but with no way to make contact, the waiting scientists had no idea what was happening; “there is a little bit of drama,” said principal investigator Alan Stern. Only one per cent of the data gathered before the flyby had been transmitted back to Earth, so there was a huge amount already to lose, and as New Horizons made its pass, there was a slim chance of a collision with a chunk of ice in the Kuiper Belt. At its

colossal speed of 14 kilometres per second (31,000 miles per hour), such a knock could have been fatal. On the ground, the Deep Space Network waited for the signal, and finally, in the early hours of the evening, a signal picked up by a radio antenna in Spain confirmed that the historic mission had been a huge success. When the high-resolution images started to arrive at mission control a day later, the team on the ground were stunned and elated. As he revealed the pictures to the public, Alan Stern said, “I don't think any of us could have imagined that it was this good of a toy store.”

This is Pluto

Randy Gladstone

John Spencer

Alan Stern

Kimberly Ennico

Randy Gladstone is an atmosphere expert. He is leading the team investigating the gases that surround Pluto, and is part of the team in control of the ultraviolet light-detecting Alice instrument.

John Spencer is the resident geology expert of the team. His job is to interpret and report on the images captured by New Horizons’ on-board cameras, giving meaning to the landscape.

Alan Stern is the principal investigator in charge of the New Horizons mission. His research career has focused on the outer Solar System and he still thinks of Pluto as a planet.

Kimberly Ennico is a specialist in imaging technology and instrument development. She is responsible for preparing and calibrating the tech on board New Horizons prior to and during the mission.

Atmospheres theme team

Imaging team leader

Principal investigator

Deputy project scientist

Some of New Horizons’ top brass react to the first datum of Pluto from the spacecraft’s closest approach

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The big dwarf planet question We speak to senior New Horizons’ deputy project scientist Dr Cathy Olkin about Pluto’s divisive status as a dwarf planet and the future of New Horizons in the Kuiper Belt A decade is a long wait from launch to target… Yes, I’ve been working on this for more than a decade and even just back in January when it turned 2015, I had to pinch myself! Then when we were getting Ralph data down from the spacecraft I was like, ‘I can’t believe we’re seeing Pluto, I can’t believe Pluto’s getting bigger!’ It feels so surreal because we’ve waited for it for so long. We can imagine that around the time it was like Curiosity’s ‘seven minutes of terror’ as the lander made its final descent? Right. I think we already had that with our reset, so I think we’re good from here! [laughs] As a planetary scientist with a particular interest in the icy worlds of the outer Solar System, this mission must be especially exciting for you. What do you hope to discover about Pluto? Many things – but by looking at Pluto we are looking at the best studied example of bodies in the Kuiper Belt, in the third zone of the Solar System past the giant planets, where there’s all these icy and rocky bodies that we didn’t really know existed. We knew of Pluto since 1930, but it wasn’t until the earlyNineties that the additional Kuiper Belt objects were

“It didn’t affect the mission… I’ll still call it a ‘planet’. That feels like the right name to me” Dr Cathy Olkin, NASA being seen. So, what I am really excited about is… the composition of Pluto’s surface and its atmosphere. To look at Pluto’s moons and have examples of what these bodies look like in this outer region of the Solar System. How was the window for taking really detailed photos of Pluto? Really detailed images started [over] a month ago when we were seeing resolutions better than we could see from the ground. So from that point forward we were learning new things every day. Can we expect New Horizons to return images of Pluto as detailed as those taken by Voyager 1, for example, on its 1979 flyby of Jupiter? There are regions that [we’ve mapped] at 200 metres [656 feet], even 100 metres [328 feet] per pixel and there are certain regions at around 70 metres [229

feet] per pixel. As Alan Stern likes to say, “If we could move New York City to Pluto, we could count the ponds in Central Park.” That’s a great way of explaining it because a lot of people can relate to that. You are project scientist for the Ralph instrument – New Horizon’s ‘eye’. Can you tell us a little bit more about it? So there are two cameras, the LORRI camera and the Ralph camera. The Ralph camera gives us colour imaging of the targets we are looking at: Pluto, Charon and the small moons. It’s also two instruments in one, the colour camera and also an infrared spectrometer. So we can look in the infrared and learn about the composition of the surface of these bodies, so it’s really a two-for-one. Pluto’s a very cold Solar System object – do you hope to penetrate the surface and look for subsurface oceans? We won’t be penetrating the surface, but we have thought that there might be an ocean beneath the surface. There could be geological manifestations of that on the surface – we might be able to infer something about that. But we won’t be probing deep into Pluto to see that. How long will New Horizons be operational? New Horizons can go on for years and years and years. I can’t give you a solid answer on that but the spacecraft is healthy, the instruments are healthy, we have a good power supply that’s working well. So there’s no end in sight. So potentially, it could go on into interstellar space like Voyager 1 and 2? Yes. That’s right – it’s what we expect will happen. Pluto was ‘downgraded’ to dwarf planet status in 2006, months after New Horizon’s launch. Did this affect the mission at all? It didn’t affect the mission and you’ll find that many of the mission scientists still refer to Pluto as a ‘planet’. It really didn’t change how I look at Pluto at all. I’ll still call it a ‘planet’ when I’m discussing it, that feels like the right name to me.

(From left) Principal investigator Alan Stern, project scientist Hal Weaver, investigator Will Grundy and project scientist Cathy Olkin

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So it was just a technicality and business as usual for you? Certainly from my perspective. I call it a planet – it has an atmosphere and moons – it seems like a planet to me.

This is Pluto

The markings on Pluto’s surface have been mapped to allow scientists to analyse the different regions of light and dark material

A close-up of Pluto’s thin atmosphere, which is collapsing back on to its surface

As New Horizons made its final approach, it captured these portraits of Pluto and its largest moon, Charon. The interesting geology was already coming into focus

These images have for the first time revealed the irregular outlines of Hydra and Nix, two of Pluto’s smaller moons

A second range of mountains was snapped at the bottom left edge of Pluto’s now famous heart. This unusual geography remains a puzzle for scientists

@ Getty Images; NASA; JHUAPL; SRI

Data gathered by New Horizon’s Ralph instrument reveals a large patch of frozen carbon monoxide at the centre of Pluto’s heart

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Exploring

Mars

Mars is a fascinating place to explore due to its amazing geology and potential for ancient life Mars is the fourth planet from the Sun and the most Earth-like of the Solar System’s other worlds. Following a distinctly elliptical orbit a little way beyond Earth, it is the outermost of the terrestrial planets: beyond it lies the asteroid belt and then the realm of giant planets. But Mars is very different from Earth: its small size, low gravity (about 38 per cent of Earth’s), cold average temperatures of around -60 degrees Celsius (-76 degrees Fahrenheit) and a very thin atmosphere that exerts about one per cent of Earth’s atmospheric pressure, means that liquid water can’t survive on the surface. So the planet today is a cold, dry desert. Nevertheless, large quantities of frozen water are trapped in its icy polar caps and in the upper layers of its red soil, within a permafrost that extends down to mid-latitudes in both hemispheres. Thanks to a tilted axis of rotation, Mars goes through a cycle

How to get there 1. Departing Earth

Any trip to Mars needs to depart around the time of opposition, when both Earth and Mars are roughly lined up on the same side of the Sun and the distance between them is at a minimum.

of seasons similar to Earth’s as, first one pole and then the other receives more sunlight. But astronomers believe that changes to Mars’s orbital characteristics create long-term cycles in the climate – it may have been significantly warmer and wetter in its past and has the potential to be more hospitable again in the future. Much further back in its history there’s evidence that Mars was rich in surface water, with a thicker atmosphere and a vast ocean covering much of its northern hemisphere. Today, the ocean floor survives in the form of vast, relatively smooth lowland plains that dominate the planet’s northern half, while heavily cratered highlands cover the southern hemisphere. It’s even possible that conditions could once have been suitable for the development of ancient microbial life, though so far this remains unproven.

Olympus Mons

Tharsis Rise

3. Arrival at Mars

The crewed spacecraft to Mars would probably be relatively small, with most of the equipment needed to survive and work on the surface placed on the surface months or years before by automated missions.

4. Long stay

By the time the spacecraft arrives, Mars and Earth will be drifting out of alignment and the distance between them increasing, so Martian astronauts would probably plan to stay on the surface for up to two years until the next opposition.

2. Short hop

The average Earth-Mars distance at opposition is 77 million km (48 million mi), though the distance travelled along a smooth transfer orbit could be up to 100 million km (62 million mi), taking about six months with currently feasible technology.

5. Return journey

The crew blast off for home in a spaceship previously landed by a robotic mission, and probably powered by rocket fuel manufactured on Mars using ice from the soil.

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Exploring Mars

How big is Mars? With a diameter of 6,779 kilometres (4,212 miles), Mars is slightly more than half the size of Earth: its surface area is 98 per cent of Earth’s dry land.

Northern polar cap

6,779km (4,212mi) wide

Mars

Northern plains

Mars

Valles Marineris

Southern highlands

How far is Mars?

The distance to Mars can vary hugely. Even when the planets line up on the same side of the Sun, its elliptical orbit means that it can be anything between 55 and 99 million kilometres (34 to 61 million miles) away.

Earth

340m (1,115ft) apart at their closest

Mars 79

Solar System

Top sights to see on Mars Despite being a small planet, Mars is home to some supersized geography. Its most famous feature is the towering peak of Olympus Mons, a vast shield volcano with a shallow, dome-like profile some 600 kilometres (373 miles) in diameter, created by the eruption of layers of lava through widespread volcanic fissures over hundreds of millions of years. At its peak, 25 kilometres (16 miles) above the average Martian surface datum (the Martian equivalent of sea level), an overlapping group of pits forms a central caldera up to 80 kilometres (50 miles) across. Olympus Mons is just the most prominent of many volcanoes: to its southeast lies an enormous bulge in the planet’s surface, known as the Tharsis Rise. This vast plateau straddles the Martian equator

Ophir Chasma

The central regions of the Valles Marineris once suffered a long, slow collapse that created this enormous valley, some 100km (62mi) wide, in the middle of the great rift valley.

at an average of eight kilometres (five miles) above the surface datum and is home to a chain of three volcanic peaks known as Tharsis Montes. Just as impressive is a deep, broad trench that runs from east to west, beginning to the southeast of the Tharsis Rise. This enormous rift, known as the Valles Marineris, is more than 4,000 kilometres (2,485 miles) long, seven kilometres (four miles) deep in places, and consists of parallel trenches with a total span of 200 kilometres (124 miles) or more. Unlike Earth’s far smaller Grand Canyon, the Valles Marineris formed not through erosion by water but along an enormous tectonic fault. The northern plains of Mars are a dusty desert coloured by reddish sands rich in iron oxide (the

Ares Vallis

Water escaping from beneath the surface of the highland regions in a catastrophic event shaped this landscape on the edge of the northern plains, carving islands that survive billions of years later.

same chemical that forms rust on Earth), but the southern highlands are densely cratered and home to winding valleys where ancient water once flowed. Close to the Martian poles, the red soil of the highlands bear an unmistakable resemblance to Earth’s glaciers, and recent space probe images suggest this is exactly what they are – slow-moving but unstoppable masses of ice disguised beneath a thin layer of reddish dust. In winter they are often covered by a bright frost of frozen carbon dioxide from the Martian atmosphere, while in summer only the colder ‘residual polar cap’, made largely of water ice, persists, displaying swirling patterns created by the sculpting effect of polar winds over millions of years.

Winding rivers

Sinuous valleys such as Reull Vallis, which runs westward into Hellas Planitia, bear the unmistakable signs that they were formed by water, flowing on the Martian surface over a long period of time.

Olympus Mons

The sheer cliffs around the summit caldera of Olympus Mons plunge vertically downwards for up to 6km (3.7mi).

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Exploring Mars

Mars’s orbit Mars orbits the Sun once every 687 days, at an average distance of 228 million kilometres (142 million miles – just over 1.5 times the Earth-Sun distance). However, its orbit is markedly elliptical, so its distance from the Sun actually varies between around 207 and 249 million kilometres (129 to 155 million miles). The tilt of the planet’s axis means that it is closest to the Sun during southern summer and furthest away during northern winter, exaggerating the effect of these seasons.

Mars

A sunset on Mars, taken by the NASA rover Spirit

Mars orbit

Earth orbit

1 Earth year = 365 days 1 Mars year = 687 Earth days or 669 sols (Martian days) Sun

Earth

780

20°C -153°C

24.1 95.3% 20

The average number of days taken for Earth and Mars Percentage of to return to carbon dioxide in the opposition Martian atmosphere

The planet’s average orbital speed in kilometres per second

Mars has complex weather, with snowfalls of frozen carbon dioxide at polar latitudes each autumn, occasional clouds of both water ice and carbon dioxide, and above all, powerful dust storms that can sometimes engulf the entire planet in an orange haze for months.

24.7 The length of a Martian day in hours 81

© Freepik.com; NASA; NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring; ESA

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Mass of Mars compared to Earth

Weather forecast

Estimated top temperature on Mars in Celsius

25.2

Current angle of Mars’s axial tilt in degrees (Earth’s is 23.4)

Mars in numbers

Traversing

Callisto

Icy Callisto is the third-largest moon in the Solar System and one of the most puzzling Callisto is the outermost of Jupiter’s four giant Galilean moons. With a diameter 40 per cent larger than our own Moon, it would be just bright enough to see with the naked eye from Earth were it not for the intense glare of light from Jupiter itself. But in fact Callisto is the faintest of all the Galilean moons, outshone not only by its inner neighbour Ganymede, the largest moon in the Solar System, but also by the significantly smaller moons Io and Europa. From up close the reasons are obvious, Callisto’s surface is overwhelmingly dark with recent craters marked by bright, icy splashes. And there are a lot of craters. In fact, some researchers think that Callisto might be the most cratered body in the entire Solar System. This is because the moon’s orbit puts it in the firing line for smaller bodies such as asteroids and comets dragged in towards Jupiter by the giant planet’s

gravity. Jupiter itself soaks up the vast majority of these impacts and while the inner moons theoretically take more of a pounding than Callisto, they all have active geology of different kinds that wipes away the worst of the damage over time. Callisto has no such internal activity and the giant moon seems to be a geologically dead world. This has been a big puzzle to astronomers, who generally assume that the larger an object is, the more geological activity it will experience in its history and the more it will be separated into distinct internal layers. Callisto’s interior, however, seems to be a jumbled mix of rock and ice and its influence on Jupiter’s magnetic field suggests there may be an ocean layer of liquid water about 100 kilometres (62 miles) beneath the crust.

How to get there 2. Venus flyby

Surprisingly, some missions to Jupiter start by heading in the wrong direction. The Galileo probe, launched in 1989, first swung past Venus in a slingshot manoeuvre that helped it pick up speed without using extra rocket fuel.

3. Interplanetary cruise Depending on the speed and alignment of the planets, the journey to the Jupiter system could take anything up to six years, as in the case of Galileo, or as little as 13 months, as with the New Horizons probe.

Valhalla

5. Rendezvous with Callisto

Repeated dips into Jupiter’s upper atmosphere could be used to alter the spacecraft orbit until it intersected with Callisto. At this point a precisely timed rocket firing would put it in orbit around the moon.

Adlinda

1. Launch from Earth Any manned mission to Callisto would probably be assembled in Earth's orbit, where large parts could be put together using several launches from the ground.

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4. Arrival at Jupiter

Jupiter’s gravity influences a huge region of space and a carefully timed engine burn would put the spacecraft into a highly elliptical orbit, close to it at one end, but further away at the other.

Traversing Callisto

How big is Callisto? Callisto’s diameter of 4,821km (2,996mi) is slightly larger than the distance across the contiguous United States, from the tip of Florida to the northwest edge of Washington State.

Hepti

Washington State

4,821km (2,996mi) wide

Florida

Igaluk Callisto Valfodr

How far is Callisto?

Callisto is an average of 780mn km (485mn mi) from the Sun. Depending on the configuration of Earth and Jupiter’s orbits, it varies between 588 and 970mn km (365 and 603mn mi) from our planet.

Lofn Heimdall

Earth

4km (2.5 mi) apart

Callisto 83

Solar System

Top sights to see on Callisto With no geological forces to reshape its surface, Callisto lacks features such as mountains, volcanoes and tectonic faults. Instead, the moon’s most spectacular structures are undoubtedly two vast impact basins known as Valhalla and Asgard and like the majority of Callisto’s features they take their names from Norse mythology. Each consists of a bright, flat region surrounded by rings of concentric hills. The bright central plains, known as palimpsests, are believed to be areas where a large impact from space broke through the moon’s dark outer crust and allowed brighter, relatively slushy ice to well up from beneath. Valhalla’s central palimpsest is about 360 kilometres (224 miles) across, but its overall diameter is about 1,900 kilometres (1,181 miles), making it one of the largest impact craters in the entire Solar System. Asgard is only a little smaller with a total

Valhalla

The Valhalla multi-ringed basin is the largest structure on Callisto, overlaid with several other major craters. It is thought to be at least 2 billion years old.

Crater haven

Over billions of years Callisto has seen more than its fair share of impacts. In fact, it's the most heavily cratered moon in the Solar System,

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diameter of 1,600 kilometres (994 miles). Careful studies of the ring structures have revealed a pattern of fractures radiating from the centre and crossing the concentric rings. Geologists think these might be linked to the presence of a hidden ocean layer about 100 kilometres (62 miles) below the surface. Other types of impressive impact-related features are crater chains known as catenae, each of which is named after a river in Norse mythology. The chains, often stretching over hundreds of kilometres were created when the multiple fragments of a comet, disrupted by Jupiter’s gravity but still following the same orbit, slammed into the moon rapidly. Astronomers saw something similar in 1994, when fragments of Comet Shoemaker-Levy 9 hit Jupiter. On a smaller scale, however, much of Callisto’s crust seems curiously eroded, small craters have

Gomul Catena

This series of depressions formed when fragments of a broken-up comet smashed into the surface of Callisto to form craters about 350km (217mi) long.

often lost their neat structure, with well-defined crater walls replaced by clusters of knob-like pinnacles, often with patches of dark debris at their bases. After studying the arrangement of these pinnacles in relation to the weak heat and light from the distant Sun, scientists have concluded that they are probably created by gradual sublimation of ice on sunward-facing slopes. Callisto’s crust is a mix of rock and various chemical ices (substances with relatively low melting points), including water and ice. Despite the intense cold, this ice can slowly transform directly into vapour at temperatures higher than around -100 degrees Celsius (-148 degrees Fahrenheit), sowly eroding Callisto's exposed outcrops into smooth isolated spires, with rock freed from the ice slowly rolling down their sides to accumulate at their bases.

Pinnacle terrain

Some equatorial regions of Callisto are studded with jagged, knob-like peaks, created as heat from the Sun steadily erodes ice out of the landscape.

Traversing Callisto

Callisto’s orbit explained Callisto follows a slightly elliptical orbit around Jupiter every 16.69 days, ranging between 1.87 and 1.90 million kilometres (1.16 and 1.18 million miles) from the giant planet. This makes it by far the most distant of the Galilean moons at almost twice the distance of Ganymede. Its distance protects the moon from the various tidal effects that influence its inner neighbours.

Europa

Io

Callisto Jupiter Callisto is seen here (bottom left) alongside Jupiter and Europa (in front of Jupiter)

Ganymede

Tidal locking

While Callisto's extreme distance from Jupiter means it isn't subject to the orbitial resonance (where planetary bodies have fallen into a regular, periodical orbit due to their gravitational influence on eachother), it's rotation is tidally locked to its orbit around Jupiter. So, like Earth's Moon, the same side always faces its parent planet.

Callisto in numbers

Weather forecast

-195°C / -105°C

km/s

0.126g Callisto’s gravity – roughly one eighth of gravity on Earth

Callisto has no weather to speak of and the most tenuous of atmospheres, composed of oxygen and carbon dioxide that is gradually lost into space, but replenished as fresh gas sublimates out of its surface ices. The surface temperature ranges between about -195°C (-319ºF) and -105°C (-157ºF).

0.054

1.834

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8.2

Callisto’s speed along its orbit around Jupiter

Callisto’s orbital period around Jupiter and its rotation period

Callisto’s mass compared to Earth

The moon’s average surface temperature

0.018

days

°C

Low

Callisto’s density Callisto’s volume in grams per cubic compared to centimetre that of Earth

16.69 -139

High

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SPACE VOLCANOES From Venus to Mars and the moons around farflung planets, volcanoes have helped shape the celestial bodies of our Solar System

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Solar System It was 2 March 1979 and the work of planetary scientists Stan Peale, Patrick Cassen and RT Reynolds was beginning to land on the desks and doormats of thousands of astronomers. Published in the journal, Science, the academic paper predicted one of Jupiter's four major moons, Io, was far from geologically dead. It stated evidence pointing to a celestial body that could be teeming with volcanic activity and as it turned out, the scientists were more than correct. Three days later on 5 March, Voyager 1 – a spacecraft launched in the late summer of 1977 – made its closest approach to Jupiter as it journeyed to unlock the hidden secrets of the Solar System's outer planets. What it discovered astounded Voyager 1's navigators at the Jet Propulsion Laboratory in California. Not least of all, astronomer Linda Morabito, who had been analysing an image taken by the spacecraft for navigation purposes and saw a puzzling feature that turned out to be a volcanic plume off the limb of Io. It was 270 kilometres (170 miles) tall, spewing sulphur into the airless sky with great ferocity, forming a persistent red ring of deposits. This volcano came to be known as Pele, after the Hawaiian fire goddess and its discovery was to be hugely significant: it was the first time that an erupting

Io: the Solar System’s most volcanic world

volcano had been found anywhere other than Earth. As such, astronomers focussed their attention further on Io. It wasn't the first time that alien volcanoes had caught the imagination. Missions to the Earth's Moon had uncovered basalt samples some 3.3 billion years old and Apollo 15 had landed close to Hadley Rille, an immense groove on the Moon 1.5 kilometres (0.9 miles) wide and 300 metres (984 feet) deep. This groove likely originated as a lava tube whose roof collapsed. The unmanned spacecraft, Mariner 9, highlighted a varied Martian terrain in 1977, which had huge volcanoes including the mammoth Olympic Mons. Yet, like the volcanoes of Mercury, these discoveries were all completely extinct. Io proved to be a myriad swirl of colours thanks to a thin atmosphere laden with sulphur. It was showing signs of being the most geologically active body in the Solar System and over the years, more than 150 active volcanoes (of more than 400 volcanoes in total) have been discovered there. Some of the moons of Saturn

and Neptune (Enceladus and Triton) have active volcanoes, Venus too, as well as the Jovian moon Europa. All of these have the potential to divulge fresh information. “Although we have volcanoes on Earth, you have to study somewhere different to understand the big picture,” says Dr Rosaly MC Lopes, a senior research scientist at NASA's Jet Propulsion Laboratory. “If you just look at your own little corner, you will not know what is possible.” Dr Lopes became interested in volcanology during her studies in astronomy at the University of London, becoming particularly hooked when Mount Etna exploded and her volcanology professor did not show up, “I thought it was really exciting to work on something where you had to rush off like that,” she says. Following her graduation she worked on the Galileo Flight Project, a mission to Jupiter that launched in 1989. She studied infrared data from Io that allowed her to detect the heat from the volcanoes. Between 1996 and 2001 she discovered 71 active volcanoes, a feat which earned her an entry in the Guinness Book Of World Records as the person to have spotted more active volcanoes than anyone else. “Io has sulphur dioxide pretty much everywhere,” Dr Lopes explains. “So you have to detect either

“I would compare the pixels of the images we received, looking for infrared hotspots that were different to the surroundings” Dr Rosaly Lopes, NASA’s Jet Propulsion Laboratory Amaterasu Patera

Paterae are shallow volcanic craters and Io has many of them. Amaterasu Patera measures 100km (62mi) in diameter and it is one of Io's darkest features. Its activity has been persistent over years of observations.

Discover some of the many volcanic systems littering the surface of Io

Loki Patera: Io's largest caldera

Known to be Io's most active hot spot, Loki Patera is the Solar System's most powerful volcano. Its heat can be detected from Earth and its depression is 200km (124mi) in diameter.

Fuchi Patera

Named after the Ainu fire goddess Kamuy Fuchi (all of the paterae are named after Sun and fire gods), Fuchi Patera is around 64km (40mi) in diameter.

Babbar Patera

Io's surface is covered with sulphur, giving the moon its colourful patchwork appearance

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Situated in the south polar region, in relative proximity to Pele, Babbar Patera shows dark deposits that scientists say are likely to include orthopyroxenes that are rich in magnesium.

The sulphur ring of Pele

First observed in 1979 by Voyager 1, Pele is ringed with red sulphur deposited by its plume. Astronomers believe it is an active lava lake since there is a very intense hot spot.

Space volcanoes the heat, plume, or a surface change to show that a volcano is active. The easiest way is to detect heat, so I would compare pixels of the images we received, looking for infrared hotspots that were different to the surroundings. We had limits of resolution and it was a lot of work but it was not that hard.” There are different types of volcanoes in the Solar System. Shield volcanoes are built up of fluid lava flows and they have broad, low-profile features. Composite volcanoes are conical, built up of ash, rock, dust and hot steam. Depending on their location in space, they either spew molten silicate rock magma or, as is the case beyond Mars, cold or frozen gases including water, ammonia or methane. What's more, volcano activity can be short or long-lived, continuing to spew for decades at a time. For instance, the volcanoes on Io stay active for very long periods of time. “They are much more powerful than the volcanoes on Earth.” says Dr Lopes. “When Voyager 1 flew past in 1979 about a dozen volcanoes were active. When Galileo visited in the late 1990s and early 2000s most of these volcanoes were still active and there were detections from the ground in-between. In July last year, the New Horizons voyage to Pluto used Jupiter as a gravity assist and we did some observations of Io at that time – again, some of the very same volcanoes were still active.” She continues: “There are some volcanoes on Earth that are always active on land. There are also volcanoes under the ocean that are harder to find. Certainly Io's volcanoes have the largest heat output and the largest calderas (craters formed by volcanic eruptions or the collapse of surface rock into a vacant magma chamber). Io is considered to be one of the most volcanically active bodies that we know of.”

Io's volcanoes are very different compared to Earth's

The most unusual volcano on Io is Loki Patera. It is the most powerful and has the largest volcanic caldera in the Solar System. There is also potential evidence of a lava lake, usually a rare occurrence but seemingly common on Io. “We want to know what is creating these lava lakes and how the eruption mechanisms work,” says Dr Lopes. “Loki Patera has some peculiar patterns, an almost cyclical pattern of eruptions that we thought we understood but then stopped... that's what happens when you study a volcano named after a trickster god!” How explosive a volcano is depends on the composition and the amount of gasses dissolved in the magma. It is often compared to shaking up

a fizzy drink bottle and opening it: if the drink has been allowed to go flat, it is likely to come out with less ferocity than one with its full soda potential. “In a volcano, you get these gasses that are dissolved in the magma,” says Dr Lopes. “When magma rises toward the surface, the pressure becomes less and the gasses want to come out. If the lava is very viscous or sticky, the gasses cannot escape easily and eventually they will come out explosively. You can get what we call a Hawaiian-type eruption where you may have this beautiful lava oozing in fountains.” Interestingly, there are differences in the ways similar types of volcano behave according to where they are. On Earth, there is a relatively thin crust that

Thomagata Patera

Thomagata Patera is situated on a sizeable shield-like area of elevated land, but it appears to be inactive since there is no observable thermal hot spot. It may be a shield volcano built of fluid lava flows.

Ah Peku Patera

With Monan Patera just north and Maui Patera close by, Ah Peku Patera is part of a trio of large volcanoes and it is south of the elongate mountain known as Monan Mons.

Pillan Patera

Pillan Patera erupted in the summer of 1997. It was the largest effusive eruption ever seen, covering an area of 125,000km2 (48,263mi2). A single measured temperature of 1,600°C (2,912°F) could imply ultramafic (low silica) composition.

Tawhaki Patera

The Prometheus plume

Constantly active since Voyager 1 first saw it in 1979, Prometheus has a plume 80km (50mi) tall. It forms at the far end of the lava flow on a plain covered with sulphur dioxide-rich snow.

Volcanic activity was first noted at Tawhaki Patera in 1997. There is also a nearby lava channel called Tawhaki Vallis, which is roughly 190km (118mi) long.

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Solar System

90

9 space peaks challenge

With weak gravity, the need for space suits and unfamiliar terrain, climbing the Solar System's volcanoes is the ultimate test

Key

Volcano height (km)

is divided into several plates gliding over the mantle. This is referred to as plate tectonics. The crusts slowly move, crash and slide into each other, propelled by the incredible heat simmering below them. When one plate is forced below another in a process called subduction, the magmas that come out in those places tend to be more viscous, forming explosive cone-shaped volcanoes. When they pull apart, more fluid basaltic lava comes out creating shield volcanoes that erupt effusively, rather than violently. Plate tectonics are an alien concept on Io, where volcanic activity originates from the tidal forces associated with its planetary neighbour, Jupiter. Io was not expected to have volcanoes since it is a small body and should have cooled a long time ago, like Earth's Moon. But as it rotates around Jupiter it is effectively squeezed as it gets closer to the planet, then moves away. Its surface is constantly being bent and flexed, which creates the necessary heat for volcanism. It's like taking a ball of wax and massaging it, making it hotter and hotter inside. “It's unusual because Io is around the size of the Earth's Moon and it should have lost a lot of its primordial heat just like the Moon has – it should have cooled down,” says Dr Lopes. “But Io is in a peculiar orbit and it has the gravitational pull of Jupiter. At the same time, the other satellites further away from Io are also experiencing this pull. The constant tug-of-war causes friction, creating heat and ensuring the interior of Io remains very molten. That is what drives volcanism on this moon.” As the volcanoes erupt on Io, it affects the entire Jovian system (the system of Jupiter's 67 known moons). The plumes, says Dr Michael Khan who works in the mission analysis office of the European Space Operations Centre at ESA, produce a ring of charged material around Jupiter and “creates a very nasty environment” as around two trillion watts of power is generated. “All of the stuff gets electrically charged and if you want to fly a spacecraft there, it gets hit by the charged particles and all of the electronics fry. It's not a nice thing to happen.” But the differences between volcanoes on different planets go beyond the causes of activity. Even patterns of eruption can be dissimilar, as is the case on Venus. “Venus can go hundreds of millions of years with no activity,” says Dr Khan, “and then everything goes off at once and the surface is completely remodelled.” Volcanoes cover around 90 per cent of Venus and its surface has been transformed by volcanic eruptions. According to Dr Lopes, who documented planets in her book, Alien Volcanoes, the Magellan spacecraft found Venus's volcanism to be young in geological terms. “There are about 1,000 volcanoes but I haven't counted them,” she laughs. “The surface is really volcanic but we don't know that much about it because it's a very challenging environment. The same is true of Io as the environment is very radiation intensive.” Planetary volcanism can mimic that of the moons too. For instance, Mars has dozens of volcanoes that are large and dominant and this is believed to be due to lower surface gravity. A thicker crust and higher eruption rates allow lava to pile on top of lava, creating extra height and bulk. Olympus Mons is 25,000 metres (82,021 feet) high. Not only is it threetimes as high as Mount Everest, but its footprint

4. Ascraeus Mons

How long would it take to climb

2. Maat Mons

25km

Location: Venus Height: 3,000m (9,843ft) : 12 days Difficulty: Moderate Maat Mons is the highest volcano on Venus. NASA says that dark lava extends from the volcano across the plains for hundreds of kilometres, but just as noteworthy is the heavy clouds of sulphuric acid and a surface temperature that reaches 477°C (890°F). However, the average grade of its slope is just four per cent.

20km

15km 1. Mount Everest

Height: 8,848m (29,029ft) : 40 days Difficulty: Hard

Location: Mars Height: 18,225m (59,793ft) : 100 days Difficulty: Hard Mars's second highest mountain is Ascraeus Mons, a large shield volcano that, like Olympus Mons, is off the northwest flank of the planet's Tharsis region. Its average flank slope is seven degrees, with the steep parts in the mid section. Plains of silicate lava flow that are rich in iron and magnesium surround it.

3. Mons Rümker

Location: Moon Height: 1,100m (3,609ft) : 1 day Difficulty: Easy Located in the flat plain of Sinus Roris in the north-western part of the Moon's near side, Mons Rümker is a solitary and extinct volcanic formation with a concentration of 30 lunar domes. The domes have a gentle, upward slope and they are among some of the smaller landscape features. Mons Huygens is the tallest mountain at 5.5km (3.4mi).

10km

5km

01

02

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5. Olympus Mons

Time it takes to complete the entire challenge, including travel time:

8. Elysium Mons

Location: Mars Height: 16,000m (52,493ft) : 80 days Difficulty: Moderate Also in the Tharsis region is Arsia Mons. Since it is a shield volcano, the slope is relatively low. Research has suggested that it may have been one of Mars's most habitable environments as its slopes were once covered in glacial ice. Its caldera is rather circular, certainly in comparison to the irregularity of Olympus Mons.

Location: Mars Height: 13,900m (46,000ft) : 70 days Difficulty: Hard As well as the Tharis region, there are three large volcanoes in the Elysium Planitia area. It includes Hecates Tholus, Albor Tholus and Elysium Mons, which is the largest volcano in this region with a base dimension of 420 x 500 x 700km (260 x 310 x 435mi). Its flanks are steeper than the shield volcanoes, making it a tricky climb.

7. Pavonis Mons

Location: Mars Height: 14,000m (45,932ft) : 70 days Difficulty: Hard The smallest of the large shield volcanoes in the Tharsis region is Pavonis Mons. Its gently sloping flanks average four degrees and there is evidence of lava tubes on the surface. These are caused by the lava crust cooling and collapsing as the flowing lava beneath it runs dry.

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9. Io volcano

Six years

6. Arsia Mons

05

Space volcanoes

Fast fact

Location: Mars Height: 25,000m (82,021ft) : 120 days Difficulty: Easy This shield volcano may be the tallest peak in the Solar System, but with a very gentle slope it gives the impression you are walking on a relatively flat surface. Once you reach the summit, marvel at the six nested calderas that make a depression of 60 x 80km (37x 50mi).

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Location: Io Height: 18,200m (59,711ft) : 80 days Difficulty: Hard It has not been possible to measure the height of Io's 400 volcanoes as yet but this moon does have the largest nonvolcanic mountain in the Solar System, the Boösaule Montes. It is northwest of the large plume deposit of the Pele volcano. The mean height of the mountains on Io is 6,300m (20,669ft).

10. Doom Mons

Location: Titan Height: 1,450m (4,757ft) : 3 days Difficulty: Hard Situated on Saturn's moon, Doom Mons is one of Titan's highest peaks and the tallest cryovolcanic mountain known in the Solar System. It could beat a climber given the snow, rain of liquid methane and ethane that might fall on it. There are also harsh winds but at least the ice-capped summit is clear.

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Solar System

Volcanoes of fire and ice

Volcanoes can blow hot and cold but what is the difference between the two types? Two main types of volcano exist in space. The first and most familiar kind is the type that spews out molten rocks, typically at high temperatures of at least 700 degrees Celsius (1,292 degrees Fahrenheit). These exist on terrestrial planets and moons that are composed primarily of metals or silicate rocks. In our Solar System they tend to be closest to the Sun. When they erupt, magma leaves the volcano and reaches the surface. It then becomes known as lava.

The volcanoes on Io, Venus and Mars are, or have been, of this type. Our Moon has also had such volcanism. “Recently, volcanism that was around 100 million years old was discovered on the Moon,” says Dr Khan, pointing to NASA's Lunar Reconnaissance Orbiter, which showed the Moon's volcanic activity gradually slowed over time. The second type of volcano is very different. Cryovolcanoes, which are colloquially known as ice

Cold volcanoes

volcanoes, still have a heated interior but they spew water mixed with ammonia or methane rather than molten rock. Cryovolcanoes exist on the icy moons such as Enceladus and Titan, which circle Saturn. “The water that comes up from the liquid ocean beneath the icy crust of these moons behaves very similarly to lava,” says Dr Lopes. “It is defined as volcanism because it's a process of bringing material to the surface.”

Main vent

Eruption

When it breaks through on Enceladus, it sends a water vapour plume and ice particles into the air. The friction heats nitrogen, which builds pressure and erupts.

The crust

Venus has a crust that is 50km (31mi) thick and it is made up of silicate rocks. Magma breaks through the crust en route to the surface.

Shield volcano

Wider than composite volcanoes, they have gentle, sloping sides and the lava is able to flow easily via vents on the volcano's surface.

As the magma seeks to escape through a composite volcano, it moves upward, making its way through a large main vent toward the crater at the top.

Hot volcanoes Multiple eruptions

When the volcano erupts over and over again, layers of hardened lava, tephra, pumice and volcanic ash builds up. A conical appearance appears as a result.

Melting ice

Tidal heating

It heats a pressurised H2O pocket that melts ices. Because the heat has to somehow escape, it begins to push upward on the body's surface.

When there is tidal friction the interior of the satellite starts to become very hot.

Secondary vents

The magma also seeks other outlets and it escapes through secondary vents. Secondary cinder cones and craters are produced as the gases and fluids find their outlet.

Shield volcano

The magma chamber of the shield volcano is spread over a wider subsurface area. Shield volcanoes have a large caldera at the summit.

Rising magma

Lava channels

Venus has lava channels, one of which is 6,800km (4,200mi) long, greater than the longest river on Earth, the Nile. It was spotted in 1991 using the imaging radar on board the Magellan spacecraft.

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As the magma rises, pressure builds. The gas-pressure build up is more intense under a composite volcano than a shield volcano, which has a far less explosive eruption.

Magma chamber

Beneath the surface of a body is molten liquid rock, pooled in what is called a magma chamber. As pressure builds, the magma seeks to find a way to the surface.

Space volcanoes

would also cover the entirety of Germany. If it existed on Earth at that size and weight, it would break through the crust and go right to the mantle. Mars also has limited plate movement, meaning the lava build up only has certain areas in which it can break through. Indeed, the surface of Mars is effectively two large tectonic plates that have been rubbing against each other. “Volcanoes are so different to each other,” says Dr Lopes. “While we have instrumentation that can give us geophysical measurements and an idea of what's underneath a volcano, there is a lot that we surprisingly don't know. There may be peculiar conditions that will make volcanoes erupt in a certain way. You only have to look at Mount St Helens in Washington, which erupted in 1980. Scientists were expecting the blast to go up but it went sideways. A lot of people were not evacuated because the scientists were not modelling for it to go this way.” Mars may also have geological structures that are referred to as mud volcanoes. They are similar to the geysers in Iceland, spewing dirt from beneath the ground. A region called Acidalia Planitia in the northern plains of Mars appears to have a fair few of these and they are also found on Earth (there is a large concentration in Azerbaijan and the adjacent Caspian Sea). “It may explain the plumes of methane in the atmosphere of Mars,” says Dr Khan, who notes

that the drastic differences and completely unpredictable nature of many volcanoes makes for very some very intriguing observations. “It tells us how differently planets can evolve even though they were created at the same time and relatively close to each other,” he says. “If you look at the exoplanets around other millions and billions of stars, how this enormous variety of different geologies can exist is a lesson that the Solar System is teaching us. It also shows the conditions for life may exist in situations where you wouldn't think it is possible.” By way of explanation, he points to Europa, another of Jupiter's geologically active moons. Like Io, it has been deformed by tides as it orbits the planets, releasing heat through rock and ice friction. The Hubble Space Telescope revealed the moon spouting water in 2013, which showed that the hypothesis of an underground ocean was probably correct. Scientists believe nutritious material is being brought to the surface. “Volcanic vents locally heat up the water and eruptions happen,” says Dr Khan. “Volcanism could be an enabler for life on Europa because it has warmth, nutritious minerals and water, which are the basic ingredients.” But just as some astronomers are looking for signs of life, so too are others keen to discover more volcanic activity on other planets and moons. Dr Lopes is hopeful that New Horizons will shed new light on Pluto where there is speculation of volcanism. It is not beyond the realms of possibility. “It's why it is important to spread your studies to other planets,” she says, “because you never know

“The conditions for life may exist in situations where you wouldn't think it is possible” Dr Michael Khan, ESA

Most of the Moon is covered with hardened lava and the ‘man in the Moon’ is made up of old basaltic flows. Some volcanic features may be less than 50 million years old what you may learn. Before we started studying Io, people wouldn't have imagined a moon that size could have active volcanism but it does.” Better equipment is helping enormously. “There have been a lot of advances in telescope instrumentation and techniques,” says Dr Lopes. “Adaptive optics are letting us observe Io to a good resolution of 100 or 200 kilometres (62 or 124 miles) on the surface. We are getting to the point where we may have smaller and cheaper telescopes that can observe these volcanic bodies very frequently.” In order to gain a better understanding, astronomers have proposed the Kuiper mission, which will put a telescope into space with an infrared instrument. Its goals include discovering whether the plumes on Europa are driven by endogenic or exogenic processes (an action or object coming within or outside of the moon). It will also look at the effects of volcanism on Io's atmosphere and its plasma torus – the cloud that encircles it. “We don't know if it will be funded but it would allow us to continuously observe Io,” says Dr Lopes. “There are certainly things we want to know about volcanism on Io, the big mystery being the composition of the lava... studying this would help us to understand lavas from the early Earth.”

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© Mark A. Garlick; Tobias Roestch; NASA; ESA; ISRO

The robotic space probe MESSENGER spent four years orbiting Mercury, uncovering the planet's volcanic past. Hills, vents and long channels have been photographed. One of the volcanoes was thought to have erupted for a billion years

Deep Space

Mammoth galaxies, gigantic black holes and trillionsof new worlds 96 The power of supermassive black holes

Take a look at the engines that give these cores a high-energy boost

104 The biggest galaxy in space

Inside the elliptical supergiant known as IC 1101

112 Earth's supernova neighbour

Observe the closest supernova in living history

120 The Shapley supercluster

Introducing the most massive supercluster in the known universe

“Within clusters, galaxies come close enough to interact, feeding on one another”

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The biggest galaxy in space 94

96

The power of supermassive black holes

112

Earth's supernova neighbour

120

The Shapley supercluster

©NASA, ESO, Nicolle Fuller

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THE POWER OF

SUPERMASSIVE

BLACK HOLES Intense, insatiable and found at the centre of galaxies, All About Space takes a look at the engines that give these cores a high-energy boost

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The power of supermassive black holes

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Deep Space The supermassive black hole is a formidable beast. Tipping the scales with a mass millions of times more than our Sun, this object wields incredibly strong gravity that’s often the subject of fear in the workings of science fiction. It is the ultimate diner of the universe, concentrating only on satisfying its insatiable appetite and chomping down on any piece of space dust, gas or even stars, planets and asteroids that stray too close to its unworldly grasp. To be clever at catching its cosmic prey though, the supermassive black hole is akin to a spider positioning itself at the centre of its web. In this case the web is its galaxy around it and the black hole sits prestigiously in the centre, the perfect place to lie in wait for its next meal. From here it uses the universe as its home delivery service, where cosmic bites are brought straight to its edge. Millions of years can go by until it gets to chow down again but when it does, everything in the vicinity gets to know about it. Bursts of brightness flash into existence and belches of speeding material shoot from these structures anytime the black hole gobbles up a snack.

The bigger the meal, the longer these super-exotic objects keep their host galaxy awake, for thousands and thousands of years on end. To be accurate, it is not the black hole itself that is lighting up with every meal – not even light can escape a black hole’s pull – but instead the environment immediately around the black hole, where the black hole’s food gathers and heats up, waiting to either be swallowed into oblivion or blasted straight back out into space again. Those supermassive black holes that are found feeding hungrily on their surroundings are the workhorses of what scientists describe as active galaxies; the black holes being the central engines that are so energetic they often shine bright enough to be regarded among the most luminous objects in the known universe. As a black hole siphons matter from nearby stars it uses its loot for the building blocks of a swirling disc of gas, known as an accretion disc, that encircles the black hole and is heated to amazingly hot temperatures of millions of degrees Celsius. Unable to keep a lid on its excitement, radiation spills from the black hole’s

“We’re not sure why only some black hole systems produce powerful jets but we’re placing our bets on the spin” Dr Alan Marscher, Institute for Astrophysical Research, Boston

vicinity in the form of powerful jets that extend great distances into space. “Between five and ten per cent of active galaxies produce a pair of powerful, oppositely directed jets containing high-energy charged particles and magnetic fields,” says Alan Marscher, who is currently based at the Institute for Astrophysical Research in Boston, USA. “We’re not sure why only some black hole systems produce powerful jets but we’re placing our bets on the spin of the black hole being an important determinant – high spins might twist up the magnetic field around the black hole so that the field acts like a coiled wire that creates a spring-like outward force on charge particles.” Marscher goes on to add that when an active galaxy does spit out a stream of high-energy particles, a wide scope of energies across the electromagnetic spectrum are covered with particles being thrown out to smash their way through space in a variety of ways, more specifically in the flavours of radio, microwave, infrared, visible, ultraviolet, X-ray and gamma rays. That’s not to say that the lower energy counterparts of active galaxies are afraid to pipe up in some wavelengths though. “In active galaxies without jets, the main radiation is across visible, ultraviolet and X-ray wavelengths, mostly from the disc of hot gas that is falling towards the black hole,” says Marscher. Despite radiating across the spectrum in all forms of light, active galaxies can be split into two camps

The engine of a powerful galaxy Pulling apart an active galaxy reveals a cosmic high-energy motor

Jets

Powerful jets are blasted out from the accretion disc around the black hole, and these jets radiate in everything from X-rays to radio waves, moving at nearly the speed of light.

Dust doughnut

A torus of dust that surrounds the black hole and its accretion disc, and glows in infrared light.

Cold gas disc

When gas first falls onto a supermassive black hole, it is still cold until it reaches near the centre of the disc.

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The power of supermassive black holes

One of the closest active galaxies to Earth at a distance of around 13 million light years, Centaurus A ejects a powerful jet

Supermassive black hole Hot gas disc

At the heart of the accretion disc, immediately around the black hole, the gas is millions of degrees hot and radiates in X-rays.

Warm gas disc

In the middle of the accretion disc, gas piles up as the disc becomes warmer and wrapped up tight by twisted magnetic fields.

The power station of an active galaxy, a supermassive black hole can be millions of times more massive than the Sun.

Hot wind

As well as jets, the accretion disc is hot enough to drive a hot wind of particles, like a superversion of the solar wind.

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Deep Space

Earth’s nearest quasar

3C 273

One of our nearest quasars lies around 2.5 billion light years away and can be seen with an amateur telescope

Virgo

Spica

Corvus Saturn

Sources of extreme energy in space Supernova remnants 4%

Active galaxies that aren’t blazars 1%

Pulsars 6%

According to the Fermi Gamma-ray Space Telescope, blazars make up over half of the objects in our galaxy

Globular clusters, highmass stellar binaries, normal galaxies and other 1%

Unknown 31%

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Blazars 57%

displaying differing degrees of intensity according to their radio wavelength emission. These two camps are radio-loud and radio-quiet. The galaxies that belong to the radio-loud group sport two very high-power streamers either side of the galaxy’s disc, produced by the jets, which eventually inflate into a pair of lobes that emit strongly in radio waves, as well as other radiation like X-rays. The Centaurus A and Perseus A galaxies are two famous examples of radio-loud galaxies. The Milky Way galaxy has something similar, but on a much smaller scale and lower power. The Milky Way’s lobes were not actually spotted through radio waves, but by a faint stream of gamma rays and X-rays seen by the NASA-owned Fermi Space Telescope. The cause of these lobes, or bubbles as they have come to be known, isn’t certain but it’s thought that the Milky Way was much more active in the past. Scientists think that millions of years ago, an intergalactic gas cloud weighing in at 10,000 times the mass of the Sun floated into and was devoured by the mega black hole, which we call Sagittarius A* (A-star), at the galaxy’s heart. It responded by blowing gigantic bubbles and jets of radiation extending 27,000 light years above and below the plane of the galactic disc. Today, our galaxy is incredibly mellow in comparison to its previous wild ways, which brings us onto the second group of galaxies: those that are radio-quiet. These are still active galaxies, but they aren’t too bothered about kicking up a fuss in radio waves. Any jets that these comparatively laid-back active galaxies possess are both quite small and are almost a half-hearted attempt at their power.

The power of supermassive black holes

Our galaxy has great lobes spewing from the top and bottom of its disc. Discovered by the Fermi Gammaray Space Telescope, it’s thought that this feature could point to a much more active past Whether a galaxy is loud or quiet helps, in part, to identify these active galaxies even further. We’ve all heard the saying, or have been asked, to look at things from a different perspective. Astronomers take this literally when it comes to these bright, long-lived objects and seemingly, the angle that these energetic objects point at the Earth holds some relevance. “Precisely what is observed is very dependent on the viewing angle,” explains Joanna Holt from Leiden University in the Netherlands. “If you look down [the centre of an active galaxy], you’ll see more ultraviolet light and you will see emissions from what are known as the narrow and broad-line regions [narrow and broad wavelength bands across the electromagnetic spectrum]. If you look at an active galaxy edge-on, you will not see the broad-line region at all and the ultraviolet light you observe will not be directly from the galaxy’s accretion disc, but the light that is scattered from particles outside a torus of dust that surrounds the accretion disc.” The model that Holt describes is called the unified model of active galactic nuclei. “The model consists of a central supermassive black hole, surrounded by an accretion disc that is then surrounded by a thick torus of obscuring material, shaped something like

a doughnut,” Holt explains. “All of this is embedded in a dense medium of clouds. The clouds that stray too close to the black hole, within the hole of the torus, are referred to as the broad-line region (BLR) and those that decide to hang back from the exotic object’s appetite and rest outside the torus are dubbed the narrow-line region (NLR).” It was American astronomer Carl Seyfert who realised in 1951 that several objects that he was observing around a lenticular galaxy (a cross between a spiral and elliptical galaxy) known as NGC 6027, seemed odd. Compared to other galactic structures he had seen, these objects had very bright star-like appearances. What’s more, Seyfert reported that these objects seemed to have broader fingerprints – or emission lines – in their light spectrum. The astronomer thought that the latter piece of information was strange – all objects that he’d studied previously had shown a spectrum that didn’t look too different to those made by stars. He’d found the active galaxies that we call Seyfert galaxies today and it was the first class of these highly energetic structures that had been found. As time has progressed, astronomers have also been able to break Seyfert galaxies into two groups – the Seyfert 1 and

Seyfert 2 galaxies, which are distinguished by the angle that these galaxy types are viewed. These two are also known as radio galaxies. “If you look directly into the centre of an active galaxy you will see a Type 1 Seyfert galaxy,” explains Holt. Since this type of galaxy has low optical luminosity, preferring to reveal themselves in the infrared, ultraviolet and X-ray bands, Seyferts belong to the radio-quiet family. Holt continues: “If the torus obscures the accretion disc, you will see a Type 2 Seyfert.” Light that is thrown out from the so-called broad-line region is scattered by a halo of hot gas that surrounds the Seyfert’s centre, allowing astronomers to grab an indirect view of what’s going on. However, it’s when an active galaxy is angled in a substantial way to its observer, when things truly start to get

“Quasars are bright and so they are much easier to detect at great distances in the universe than normal galaxies” Joanna Holt, Leiden University

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Deep Space

Active galaxy types

The equivalent power of

10 trillion Suns Blazar

Radio galaxy

Angle to observer: 0-90 degrees

Angle to observer: less than 10 degrees

These active galaxies point their jets directly at their observer, spitting out their high-energy jets that move extremely close to the speed of light.

These active galaxies provide jets that produce radio-emitting lobes of highenergy particles.

interesting. “If we are looking within a few tens of degrees of the jet axis, we see more radiation that is beamed by the jets because they are travelling at a speed very close to that of light,” says Marscher. “This causes the radiation to be beamed like a halogen flashlight in the direction of the jet outflow.” He is of course, referring to the radio-loud quasars, distant dazzlers with centres that are around 1,000 times brighter than all of the host galaxy’s stars put together. “Quasars are bright and so much easier to detect at great distances in the universe than normal galaxies. They are rare but their numbers increase

as you come across the less luminous type of active galaxy. Numbers also increase when you look back to 3 billion years after the Big Bang.” The quasar might be an attention-grabber but when it comes to overly intense galaxies, the blazar takes the crown – that’s because when they’re watched, the observer is in the line of fire. “In a blazar, the jet is pointing within several degrees of our line of sight, so the beaming is extreme,” says Marscher. “Also, the jet is flowing towards us at up to 99.9 per cent of the speed of light, that means that events that occur in the jet are sped up and

“In a blazar, the jet is pointing within several degrees of our line of sight, so the beaming is extreme” Dr Alan Marscher, Institute for Astrophysical Research, Boston

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The power of supermassive black holes

The equivalent power of

1,000 trillion Suns

Quasar

Angle to observer: 10-30 degrees

One of the most energetic types of active galaxy, they are so bright they can be seen across the universe.

The equivalent power of

100 trillion Suns

Quasars ultimately block star-forming in their galaxies completely, turning them 'red and dead' © Leiden University PR; Boston University PR; NASA; Sayo Studio; Science Photo Library; NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring

take much less time to occur from our point of view.” Furthermore, he says, the brightness we see is coming from within around ten light years of a black hole and noticeably changes on a time-scale as short as a matter of minutes. “We also see a bright microwave-emitting ‘blob’ moving at speeds that appear – just an illusion – to be faster than light.” Being the bearer of these exotic objects, active galaxies don’t get off scot-free from the effects of the monstrous black holes within them. The intense radiation pouring out from them can heat the starforming hydrogen gas in the galaxy, causing it to become too hot to form stars. If the galaxy is active enough, it can even blow this gas away, ejecting it from the galaxy. When this happens, star forming comes to an end in the galaxy and, over time, it becomes what astronomers call ‘red and dead’. So quasars and blazars may shine the brightest over a short time, but in the long run they’re doomed to die from the inside out.

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THE BIGGEST GALAXY IN SPACE

A billion light years from the Earth lies an elliptical supergiant of incredible proportions: IC 1101 is the largest known galaxy in the universe, illuminated by the glow of 100 trillion stars

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Deep Space The stars that adorn the night sky might be light years apart, but they do not exist in isolation. They are bound up in dark matter, caught in a mutual gravitational waltz that sees them drawn in slow orbits around the centres of enormous galaxies. The galaxies themselves collect together in groups, and the groups form clusters. Within clusters, galaxies come close enough to interact, feeding on one another in acts of galactic cannibalism, and accumulating vast quantities of dust, gas and stars in violent mergers. The end products of the most spectacular collisions are the supergiant elliptical galaxies, some of which number among the largest galaxies in the known universe. At over 30 times the diameter of the Milky Way, the unimaginatively named IC 1101 holds the title of ‘largest galaxy’, spanning a region of space measuring around 3 million light years. First recorded in the 1890s by astronomer Lewis Swift, it was later catalogued as a ‘nebulous feature’ by John Louis Emil Dreyer and remained an unidentified cloud of dust and gas for several years. By the Thirties Edwin

Hubble had begun identifying some of these ‘nebulae’ as galaxies, so it wasn’t long before the true identity of IC 1101 was revealed. The enormous galaxy is located just over a billion light years away between the constellations of Virgo and Serpens; easily found by following the arc of the Big Dipper southeast towards the bright star Arcturus, and just northeast of the brightest star in Virgo, Spica. Virgo is the second largest constellation in the night sky, and is home to the Virgo cluster, a large group of interacting galaxies just over 50 million light years from the Earth. The cluster contains a spectacular array of objects, including one of the most massive supergiant elliptical galaxies in the known universe, M87. Barely wider than the Milky Way, this dense galaxy has an estimated 1,000 times more mass.   Far in the distance, beyond these nearby galaxies, a much larger object can be seen from the ground: the Abell 2029 galaxy cluster, and at its centre, IC 1101. Abell 2029 is vast. Its outline spans several

million light years, encompassing thousands of galaxies. In order to hold itself together it must contain dark matter with a mass equivalent to over a hundred trillion Suns. The unseen matter traps a halo of gas, superheated to millions of degrees and visible as a diffuse envelope of X-rays. The galaxies in the cluster are not evenly distributed and the core is dominated by IC 1101, a type-cD galaxy with a halo of stars and an enormous dustless envelope. Though it is just one of the thousands of galaxies in Abell 2029, IC 1101 accounts for a significant proportion of the entire cluster’s diameter and total light emitted, effortlessly earning it the title ‘brightest cluster galaxy’ (BCG), the most luminous object in Abell 2029. Other supermassive galaxies have been identified, but none are able to compete with the vast outline of IC 1101. It dwarfs every other galaxy identified to date. The largest spiral galaxy, NGC 6872, has two spiral arms, the tips of which are a staggering 522,000 light years apart, but even at that size, it is less than a fifth of the width of IC 1101.

The Abell 2029 cluster

IC 1101 sits at the heart of one of the largest and most luminous galaxy clusters in the sky IC 1101 is located right at the centre of a densely populated galaxy cluster known as Abell 2029. IC 1101 takes up a 3 million-light-year stretch of the space at the cluster’s core, accounting for a huge percentage of the overall light emitted. Around it are numerous other galaxies, of all shapes and sizes but the majority of the cluster is unseen, and an estimated 70 to 90 per cent is made up of dark matter. The entire group is shrouded in dust and gas, reaching temperatures in the millions of degrees.

IC 1101

This elliptical supergiant is at the heart of the galaxy cluster, dwarfing its companions, and accounting for a quarter of the emitted light.

Cold dark matter

Most of the mass of the galaxy cluster is thought to be dark matter, increasing in density towards the centre.

Other galaxies

IC 1101 might dominate the cluster, but around its perimeter are thousands upon thousands of galaxies of all different shapes and sizes.

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The biggest galaxy in space

How big is IC 1101?

It is hard to imagine the true scale of a galaxy measuring 3 million light years across, but comparing IC 1101 to familiar landmarks helps to illustrate its size. Our own galaxy, the Milky Way, measures around 100,000 light years in diameter, while our nearest neighbouring spiral galaxy, Andromeda, is larger, at around 220,000 light years. Both are dwarfed by IC 1101. The Milky Way has a number of satellite galaxies, including the Large and Small Magellanic Clouds, the Leo and Boötes galaxies, and Sagittarius Dwarf. The farthest of these is 1.4 million light years away and even taking into account the entire set, IC 1101 would be wider. In fact, if IC 1101 was positioned between the Milky Way and Andromeda, it would fill all of the space in between, and still manage to engulf them both.

SMC

Diameter: 7,000ly

LMC

Diameter: 14,000ly

Sculptor

Diameter: 70,000ly

Bode's galaxy

Diameter: 95,000ly

3,00 0,00 0ly Milky Way

Diameter: 100,000ly

NGC 1365

Diameter: 200,000ly

Andromeda

Diameter: 220,000ly

IC 1101

Diameter: 3,000,000ly

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Deep Space

Inside and out

The sheer scale of this galactic daddy is evidence of its violent past The largest galaxies in the universe are the supergiant ellipticals. Many were once orderly spiral galaxies but violent collisions have distorted their outlines, disrupting their structure and burning through their remaining fuel. Around the edges of IC 1101, a faint envelope marks the remnants of the galaxies that were obliterated by the supergiant. In the centre, lowmass stars move in chaotic orbits, burning with a gentle yellow-orange glow that indicates that they are nearing the end of their lives. Elliptical galaxies are divided into eight classes according to their shape, with ‘0’ being almost spherical and ‘7’ being extremely elongated. According to this sequence, known as the ‘Hubble Tuning Fork’, IC 1101, with its fat and slightly flattened core, is classed as an E3. IC 1101 is located right at the centre of the Abell 2029 galaxy cluster, a position perfect for accumulating matter, but it is possible that it wasn’t always there. As a large galaxy moves through a cluster, it interacts with its smaller neighbours, accumulating a tail of galaxies and dark matter caught up in its gravitational wake. These smaller galaxies pull back against their larger captor, slowing its motion by a process known as dynamical friction. As the large galaxy slows down, it spirals towards the centre of the cluster, dragging all of the trailing galaxies with it. At this central point, they begin to collide. As galaxies crash through one another, their gas and dust mixes, and their structures become distorted. Amid the chaos, a flurry of star formation is

triggered, draining the remaining resources of the merging galaxies. This can be seen in the Antennae Galaxies, a pair of interacting spirals found in the constellation of Corvus. In the early stages of a merger, their dust and gas is beginning to collide, resulting in an impressive starburst as matter comes together to form new stars. The centre of IC 1101 is radio bright, indicating the presence of a supermassive black hole. This is a feature typical of most large galaxies and as they spiral towards a collision, the interaction between these enormous masses plays a significant role in shaping the new, combined galaxy. The intense interaction is strong enough to jettison entire star systems from the merging galaxies, flinging them outwards into space. The hungry black holes strip what remains, feeding on the dust and gas left over after the merger. What is left is an elliptical core of ageing stars and a dustless envelope. The signatures of past collisions are evident in this halo, with recent or ongoing mergers creating obvious clumps. Some supergiant elliptical galaxies continue to grow gradually, accumulating matter from many smaller galaxies as they pass, while others form as part of a dramatic merger, before settling back into a more balanced state. The halo surrounding IC 1101 is smooth and spread out, indicating that it has probably existed undisturbed for an extended period of time, and that it formed much earlier on in the history of the A2029 cluster in one monumental collision.

When galaxies collide

This combined Spitzer and Hubble image of two merging galaxies, known together as II Zw 096, highlights the infrared chaos as galaxies combine

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Known as ‘red and dead’, elliptical galaxies represent the final stages of galaxy evolution; the product of monumental collisions between rich disc galaxies. Although the history of IC 1101 remains unknown, similar mergers are occurring across the universe, allowing astronomers to view the stages that lead up to the creation of the largest galaxies. The Mice Galaxies are in the early stages of a merger, and are named by virtue of the long tails of dust and gas spinning out behind them as they circle one another in a death spiral. As galaxies get closer, clouds of dust and gas crash through one another, releasing huge amounts of energy. The disrupted matter clumps and clusters, and triggers a flurry of star formation known as a starburst. As things start to settle down, the remaining dust and gas coalesces to form a vague sphere, surrounded by a fuzzy, dustless halo, and lit by the remaining dying stars, like IC 1101.

Smooth envelope

The halo enveloping the galaxy represents the remnants of past interactions. It is smooth, and free of clumps, indicating that IC 1101 has been a stable size for some time.

Radio centre

The core of IC 1101 is emitting radio waves, hinting at the presence of a supermassive black hole, a common feature of both spiral and elliptical galaxies.

The biggest galaxy in space

By the numbers

3,000,000

Crowded neighbourhood

Like other supergiant elliptical galaxies, IC 1101 is in a crowded area of space, positioned at the very heart of one of the most populated galaxy clusters in the observable universe.

25

Per cent of the light emitted by the Abell 2029 cluster comes from IC 1101

The apparent magnitude of the galaxy, making it visible with ground-based telescopes

The minimum number of Milky Waysized galaxies that would fit end-to-end inside IC 1101

The estimated diameter of IC 1101 in light years

14.7

Elongated core

The characteristic feature of an elliptical galaxy is a central core of stars, dust, and gas, forming a squashed sphere.

Orange glow

The majority of the stars in IC 1101 are ageing, and many are older than the Sun. Most of the dust and gas has been spent, and the remaining stars are metal-rich and glow yellow-orange.

1.07

30

The distance to IC 1101 in billions of light years

100 trillion The number of stars contained within the galaxy

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Deep Space

Imaging IC 1101 This massive galaxy is visible from Earth, even at a distance of 1 billion light years

Despite the phenomenal distance between us and the largest galaxy in the universe, the bright glow of IC 1101 is still visible from the ground. It was first recorded by American astronomer Lewis Swift. He made a series of observations together with his son Edward from the Warner Observatory in New York in the late 19th century. It was categorised as a nebula as it was not known at the time that galaxies other than our own existed. Over a century later the object was recorded as the 1,101st item in the Index Catalogue of Nebulae and Star Clusters by Danish-Irish astronomer John Louis Emil Dreyer. Its true nature remained a mystery until the Twenties when Edwin Hubble looked at our closest galactic neighbour, Andromeda, and for the first time he saw that the cloud contained stars. Since then, the various ‘nebulous objects’ in the IC catalogue have been studied more closely, and with more powerful instruments.

The most comprehensive galaxy survey of galaxy size was completed by NASA’s Galaxy Evolution Explorer (GALEX) before it was decommissioned in 2012. Using ultraviolet light, it mapped the distances and sizes of thousands of galaxies, some almost as old as the universe itself and even then, no galaxy wider in diameter than IC 1101 was found. Images captured by the Kitt Peak Telescope in Arizona were the first to show the scale of IC 1101. The sheer volume of stars within the galaxy make it one of the most luminous ever identified, and at magnitude 14.7 it was easily observed with groundbased telescopes. The structure was described as large and organised, and its smooth, even outline hinted that it must be incredibly old, formed around the same time as the galaxy cluster itself, and then stabilised over the following millennia. Much of the study of IC 1101 has been performed using radio telescopes. Radio waves are able to

“The maps produced indicate the presence of a supermassive black hole”

Neighbouring galaxies

The visible light emitted by IC 1101 is mainly in the red/orange part of the spectrum, released by the low mass stars in its core

Chandra reveals the cloud of hot gas that envelops the Abell 2029 cluster, and IC 1101 at its core

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permeate the dust and the gas, allowing astronomers to look into the heart of the galaxy. The maps produced by telescopes reveal the core of the galaxy, indicating the presence of a supermassive black hole, and providing clues about the history of the galaxy and its parent cluster. The Chandra X-ray Observatory has also been used to probe the hot gas that surrounds Abell 2029 and IC 1101. The halo is smooth, and increases gradually in intensity from the outer edges to the centre, representing gas heated to several million degrees. Measuring the heat and intensity has allowed astronomers to map the slow-moving, cold dark matter that clogs the core of the galaxy cluster, revealing that this mysterious substance accounts for 70 to 90 per cent of the entire mass of the cluster. NASA’s Origins programme and the James Webb Space Telescope, which is set to launch in 2018, will allow us to look back further into the history of the universe than ever before, allowing astronomers to view the earliest stages in galaxy evolution and to untangle the physics behind the formation of enormous galaxies like IC 1101.

This composite image shows the vast scale of IC 1101. In blue are the galaxies of the Abell 2029 cluster, captured at the Kitt Peak National Observatory in Arizona, USA, and superimposed in red is the signature of the hot gas envelope that shrouds the cluster, held in place by an enormous quantity of unseen dark matter, and imaged by the Chandra X-Ray Observatory. The elongated core of IC 1101 is visible at the very centre.

The biggest galaxy in space

GALEX

Solar cells

The Galaxy Evolution Explorer (GALEX) launched in 2003, and performed the first space UV sky survey. Weighing just 280 kilograms (617 pounds), this small orbiting telescope was designed to capture images of galaxies near, and far, and to determine their size, distance and rate of star formation. The images captured ranged from all-sky to ultra deep and revealed nearby giants, as well as distant galaxies over 10 billion years old. The extremely sensitive ultraviolet detectors on board can capture the emissions of even the youngest, hottest stars, allowing GALEX to map the size of galaxies in unprecedented detail. By probing at the outer edges of galaxies for hidden material, the explorer has provided more accurate measurements of existing galaxies, and revealed the largest spiral galaxy to date, NGC 6872.

300 watts of power were supplied to the craft by gallium-arsenide solar panels, measuring 2.8m (9.2ft) across.

Facing away

The instruments on board were too sensitive to face bright UV sources, like the Earth, the Sun, or any of the stars visible from the ground.

Ritchey-Chrétien telescope

At the heart of GALEX is a 50cm (20in) ultraviolet telescope with a 1.2-degreewide field of view.

Compact design

© NASA; Kitt Peak; Chandra; Adrian Mann; Nicolle Fuller: ESO; JPL Caltech; DSS; UCI; A.Lewis; STScI

At launch, the solar panels were wrapped around the explorer, allowing it to fit on the end of the Pegasus launch vehicle.

Star tracker

The direction of the telescope was determined by a star tracker in combination with a Sun detector, allowing it to focus in on a single area of the sky without damaging the sensors.

Detectors

GALEX contains two detectors within its shell, covering the far and near ends of the ultraviolet spectrum.

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EARTH’S SUPERNOVA NEIGHBOUR As astronomers watch the story of SN1987A unfold before their eyes, they are observing the closest supernova in living history and gradually uncovering its turbulent past

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Deep Space When SN1987A exploded in 1987, no one was expecting the blast. The star behind it all, an unassuming blue supergiant, was an extremely unlikely candidate for a supernova, so when it happened every scope in the Southern Hemisphere turned to face the Large Magellanic Cloud (LMC). This irregular galaxy is less than 200,000 light years from the Sun, making it one of the closest galaxies to the Earth. It measures around 14,000 light years across at its widest point – around an eighth of the diameter of the Milky Way. Located in the southern sky, between the constellations Dorado and Mensa, the LMC is visible all year round from latitudes below 20 degrees south. It appears as a faint white smudge around 20 times the total width of the full Moon. The LMC is actually a satellite trapped in orbit around the Milky Way and with a total mass no more than a hundredth of its captor, the galaxy is a relative dwarf. Although it has an obvious bar of stars in the centre, the gravitational pull of our own galaxy has distorted its structure, and tidal interactions with the nearby Small Magellanic Cloud have created a bridge of gas between the two. The local disruption fuels the star formation, so the LMC contains several bright clouds of molecular gas including the Tarantula nebula, which is home to some of the most massive stars in the known universe. Large stars burn through their fuel rapidly, collapsing in a dramatic blaze and scattered across the field of molecular gas are the remnants of dozens of supernovae. However, none is quite so interesting as SN1987A.

On the very outskirts of the nebula is a young star cluster that formed around 12 million years ago. Here, 500 Sun-sized stars are joined by 12 massive blue supergiants and nestled among them is SN1987A, the closest supernova to be witnessed since the invention of the telescope. SN1987A was a red supergiant, before losing some of its mass to become a blue supergiant similar in size and brightness to its companions. However, as it neared the end of its life, the star underwent a catastrophic collapse. On the night of 23 February 1987, a research assistant from the University of Toronto set up a routine long-exposure image of the LMC – but when he developed the plate, something was different. A new, extremely bright star had appeared in the image. By morning, two other astronomers had also spotted the supernova and news rapidly spread to observatories across the world. The explosion produced radioactive nickel and in the three months following the initial blast, the brightness of SN1987A grew steadily as the metal decayed into cobalt and then iron. At its brightest, it reached an apparent magnitude of three, making it visible with the naked eye even in a brightly lit city. Despite its brightness, SN1987A was difficult to view from the ground, and it wasn’t until the launch of the Hubble Space Telescope in April 1990 that astronomers were able to get a closer look at the young supernova. It’s now the best-studied supernova in history and astronomers will have a front-row seat as the collapsed star continues to evolve in the coming years.

Too close for comfort?

SN1987A is not the closest supernova ever witnessed. In 1604, Kepler’s Supernova exploded inside the Milky Way, just 20,000 light years from the Earth. In the absence of modern technology, the aftermath of this phenomenal event could only be recorded from the ground. The unusual ring structure surrounding SN1987A was key in determining its distance from the Earth. The inner ring lit up a year after the initial explosion, setting its radius at one light year. By drawing an imaginary triangle between the edge of the inner ring, the supernova itself and the Earth, astronomers were able to use trigonometry to calculate the distance to the dying star.

Kepler’s supernova (20,000ly)

SN1987A (168,000ly)

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Where is SN1987A? The surprising SN1987A supernova was traced to the outskirts of the Tarantula nebula

The Tarantula nebula is one of the brightest nebulae in the sky. It is also one of the most active areas of star formations in nearby space, where the twisted clouds of partially ionised hydrogen gas conceal over 800,000 stars. The nebula is littered with the remnants of burnt-out supernovae. Individual star clusters formed sporadically, bursting into life as massive supergiants, racing through their fuel and then dramatically disappearing in a shower of gas and radiation, but SN1987A is unique. It’s the closest supernova to Earth to have exploded since the invention of the telescope and we have learned more from it than from all of the older remnants in the Tarantula nebula combined.

Earth’s supernova neighbour

R136a1

The Tarantula nebula is also home to the most massive known star. R136a1 is an astonishing 265 times the mass of the Sun.

NGC 2060

Near the centre of the nebula is the NGC 2060 cluster, containing a 5,000-year-old supernova remnant.

SN1987a

Earth’s closest supernova is located on the outer edge of the nebula, in a cluster of other blue supergiants that all formed around 12 million years ago.

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Deep Space

Inside and out

SN1987A’s 27-year evolution has changed the way we think about supernovas By the late 1980s, there was already a theoretical model predicting the aftermath of the death of a massive star, but none had ever been observed up close. The fresh explosion of SN1987A offered astronomers a rare opportunity to watch a cosmic event unfold in real-time, over the course of years, not centuries – but this supernova was unusual. The catalyst star of SN1987A, Sanduleak -69 202, didn’t fit the profile of a star about to collapse. It was a blue supergiant of around 20 times the mass of the Sun, not the red supergiant that scientists were expecting. It was also surrounded by three distinct rings of glowing gas, created several thousand years before the star died. These unusual halos have enabled astronomers to track the progress of the shock wave as it races

away from the supernova, lighting up like a beacon whenever a collision occurs. The rings themselves are moving away from SN1987A at the (relatively) slow speed of around 160,000 kilometres (100,000 miles) per hour, but the debris from the explosion is moving at least 100 times faster. When the star ran out of fuel and the core collapsed, a fraction of the energy from the explosion escaped, racing through the gas rings and causing them to glow. After this initial hit, the light faded. But in 1997, the debris from the supernova started to catch up with the inner ring. A single spot of bright activity appeared on the north side and by 2000 there were several more to the south. As the debris ejected from the centre of the explosion collided with the hot plasma, the impact

Supernova signature Key features of this stellar gravestone 1. Debris A cloud of dust and gas from the remnants of SN1987A is expanding outwards from the centre, rushing towards the inner ring at 32 million kilometres (20 million miles) per hour. 2. Inner ring The bright inner ring surrounding SN1987A was formed around 20,000 years before the catalyst star turned supernova. It measures roughly one light year across. 3. String of pearls As clumps of debris collide with the ring, they create a shock wave, leading to the release of X-rays, which make the dust and gas glow. 4. Outer rings Although the outer rings appear offset from the centre of the star, this is an illusion based on our relative positions in space. In reality, the two rings lie in a straight line, one in front of SN1987A and the other behind. 5. Unknown remains What remains of the core of SN1987A is unknown. Some scientists believe there is a neutron star lying at the centre, others think that it might be a small black hole.

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03 04

05 01

02

created shockwaves, releasing bursts of X-rays. The radiation excited the gas and dust in the debris cloud, causing it to glow. That was just the beginning – in 2011 the bulk of the debris began to slam into the inner ring, lighting up the entire circumference and as the main front of the shockwave continues to collide with the remnants of the ring, the material will eventually be blown away into the LMC. What will remain of SN1987A is currently unknown. During a supernova explosion, the matter that once made up the core of the star collapses inwards, compressing together so tightly that the protons and electrons are combined to form an incredibly dense object known as a neutron star. However, so far the remains of SN1987A are curiously missing entirely.

Earth’s supernova neighbour The supernova released such a vast quantity of dust that the centre of the blast zone is entirely obscured. Neutron stars tend to appear as pulsars, releasing streams of X-rays as they spin, but it often takes several hundred years for these signals to appear. At this early stage, Astronomers watch for evidence that a dense star might be pulling in matter from the dust cloud, but so far nothing has been observed. Some scientists believe there is actually a small black hole at the centre, but this raises difficult questions about how the neutrinos that hit Earth’s telescopes could have escaped in the first place. Others hypothesise that it might be a quark star, but the existence of such densely compacted matter has yet to be observed.

For now, the identity of the remnant at the heart of SN1987A remains a mystery. xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx

Almost 20 years after SN1987A exploded, Hubble’s Advanced Camera for Surveys captured this image of the aftermath. The inner ring is glowing under the impact of debris collisions

“Astronomers watch for evidence that a dense star might be pulling in matter from the dust cloud” SN1987A’s unusual history means scientists are only now beginning to piece together the events leading up to its explosive demise

"This is a photo the SN1987A remnant taken by the Hubble Space telescope in 2012. We're only beginning to understand what its ring formation is."

20,000

168,000 Earth masses of radioactive iron released

LIGHT YEARS 57

10

The distance from Earth to SN1987A

Rings of death

At the time it went supernova, SN1987A was a blue supergiant measuring around 40 times the diameter of the Sun. But just 30,000 years before, it was a red supergiant and a star around five times the mass of the Sun was on a collision path with its core. As the smaller star circled towards the centre of the supergiant, it whipped up the atmosphere, flattening it into a disc. The spiralling stellar missile heated the gas as

By the numbers

it passed through, causing it to expand outwards. The ejected material settled above and below the disc, forming two distinct rings. After the collision, the energised core of the merged star spun faster and even more gas was thrown off into space, shrinking the supergiant and forming the third ring. This catastrophic event could well have been the catalyst that initiated the supernova.

10

The number of ultraviolet and X-ray photons released by the explosion

million

degrees C

The temperature of the expanding gas shell

5,000 km/s The expansion rate of the young supernova blast

200,000 Earth masses of dust created

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Deep Space

Observing SN1987A

Since the first neutrinos from the blast hit Earth in 1987, astronomers have watched this unique supernova evolve

On the night of its explosion, very few telescopes were aimed at SN1987A and just three people are known to have witnessed the first light of the supernova. Two of these men were based at the Las Campanas Observatory in the Chilean Andes, home to two 6.5-metre Magellan telescopes. The other was an amateur astronomer observing the LMC using a 0.3-metre telescope in New Zealand. These were not the first signals to reach the Earth, however. Two hours before the first light of the supernova was spotted, neutrinos from the blast reached our particle detectors. The Kamiokande II neutrino telescope in Japan is positioned 1,000 metres (3,300 feet) below the ground in the Kamioka mine. On 23 February 1987, the detector was hit by nine neutrinos in the space of two seconds and another three just a few seconds later. Two other telescopes, the IMB detector in Ohio and the Baksan telescope in Russia, also recorded the event, together counting a total of 25 neutrinos. This might not sound like much compared with the billions upon billions released by a supernova explosion, but neutrinos are almost massless and don’t really interact with matter. Most of them race through the Earth without colliding with anything, making their presence extremely hard to detect. The number picked up by the telescopes was huge, and provided the first real evidence of established supernova theory. At the time of the blast, the most advanced ultraviolet telescope in orbit was the Soviet Astron, which became the first space telescope to image the supernova, but it ceased to function in 1989. Luckily, the Hubble Space Telescope was almost ready for launch, so since 1990 it’s been documenting the progress of SN1987A in hundreds of images. Not only did Hubble reveal the three rings that surround the supernova but, in combination with the Chandra X-ray Observatory, it has been using them to track the progress of the central shockwave, watching as matter from the core of the explosion began to collide with the gas that makes up the ring.

“Around 200 thousand Earths could be formed from the dust” 118

The heat of the explosion is well documented, but recently infrared telescopes have also begun probing the heart of the supernova. The centre of SN1987A is obscured and the infrared equipment on board the European Space Agency’s Herschel Space Observatory revealed an enormous cloud of cold dust, spewed out by the explosion. It’s estimated that around 200,000 planets the size of Earth could be formed from the dusty outpourings of SN1987A. The destruction of the rings around the supernova will be complete within our lifetime, and space telescopes will be able to create an unprecedented timeline of the end of SN1987A’s life. As the dust and debris are blown away, advanced instruments like the James Webb Space Telescope will be able to probe the core of the blast, finally identifying the remains of SN1987A. This image reveals the three rings in stunning detail, and shows how much the keyholeshaped cloud of debris has grown since the first explosion

In 1998, Hubble revealed a single hotspot on the edge of the inner ring

By 2000, several more hot gas balls had appeared on the opposite side of the ring

In 2003 almost the entire inner ring was alight as dust and debris from SN1987A tried to pass through

Earth’s supernova neighbour

Ultraviolet telescope

Sensor-driven mirror

The secondary mirror inside the UV telescope was controlled using a series of sensors, keeping the telescope steady to within one arcsecond (1/3,600 of a degree).

A Soviet satellite, Astron, was launched in March 1983 and was equipped to detect ultraviolet and X-ray radiation. The telescope was only designed to operate for one year, but at the time of SN1987A’s discovery four years later, the Astron was still functional. As the largest ultraviolet space telescope in orbit at the time, it was quickly directed towards the LMC. From 4 to 12 March 1987, Astron captured images of the new supernova, becoming the first space telescope to record the event. By June 1989, the satellite had ceased to function but with the launch of the Hubble Space Telescope in 1990, the view of SN1987A was about to get significantly clearer.

UV telescope

The main instrument on board the Astron was a five-metre (16foot) long ultraviolet telescope, built as part of a collaboration between the USSR and France.

Main bus

© ALMA; ESO; NAOJ; NRAO; A. Angelich; Visible light image: the NASA/ESA Hubble Space Telescope. X-Ray image: The NASA Chandra X-Ray Observatory; ESA; P. Challis, R. Kirshner (Harvard-Smithsonian Center for Astrophysics) and B. Sugerman (STScI); D.Burrows (PSU) et al., Optical: P.Challis (CfA) ; L. Calçada

The Astron satellite was built on the same design as the Venus probe, Venera 4, with a central bus containing the scientific payload.

Solar power

The satellite, and its equipment, were powered by solar panels attached as two wings, one on either side of the bus.

X-ray vision

Peering within the blast

Images from Hubble (green) and Chandra (blue) show the collisions occurring on the inner surface of the ring, while radio data from ALMA (red) reveals the cold dust created by the supernova

This X-ray heatmap from the Chandra X-ray observatory shows debris slamming into the inner ring. As the speeding cloud tears through the ten-million-degree Celsius plasma that encircles SN1987A, the shockwave creates X-rays, exciting the gas and causing it to glow. The light of the initial explosion has now faded, replaced by light emitted as the exploded debris cloud tears through the surrounding gas and dust, marking the transition of SN1987A from supernova to supernova remnant – the final display of a deceased star.

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THE SHAPLEY

SUPERCLUSTER Introducing the most massive supercluster in the known universe, a dense collection of over 8,000 individual galaxies that are over 500 million light years from the Earth 121

Deep Space Galaxies rarely exist as isolated entities. As the universe expanded after the Big Bang, the distribution of matter was not entirely uniform, so instead of spreading out evenly, clumps grouped together. Mutual gravitational attraction gathered stars into galaxies, which in turn collected to form groups. These groups then associated into clusters, which came together to form superclusters. The universe became a web of densely compacted galaxies interspersed with vast voids, like a network of soap bubbles surrounded by matter and filled with empty space. Our own Milky Way is part of the Local Group, a collection of 54 gravitationally interacting galaxies, including our nearest spiral neighbour Andromeda. The Local Group makes up part of the Virgo cluster, which in turn is part of a larger collection of around 47,000 galaxies, known as the

Virgo supercluster. This measures a huge 110 million light years across. Beyond our home supercluster, there are many others that we know of. The richly populated Coma supercluster contains over 3,000 galaxies, most of which are elliptical or lenticular in shape, and some of which are thought to be almost as old as the universe itself. It lies to the north of the plane of the Milky Way and can be observed unobscured, enabling astronomers to peer into the heart of the cluster as neighbouring galaxy groups begin to collide. However, by far the most massive supercluster in the observable universe is Shapley, also known as the Shapley concentration. This supercluster is a collection of over 8,000 galaxies, with a total mass estimated at more than 10 million billion times that of the Sun. Many of the concentration’s member clusters

number among the richest and brightest in the sky. The supercluster lies to the north of the constellation Centaurus and despite its massive scale was only identified relatively recently. It’s over 500 million light years from the Earth and is in an awkward position for imaging, obscured by the stars and dust of the Milky Way. In a project that began in the 1920s, Harlow Shapley and his colleagues at Harvard University charted the galaxies in the southern sky and identified an enormous elongated cloud in the direction of the constellation Centaurus. The supercluster remained largely unstudied for decades, but interest in the galaxies reignited in the 1980s after the discovery that a closer superstructure, Hydra-Centaurus, might be harbouring an entity known as the Great Attractor. This is

Nearby superstructures

Shapley eclipses closer superstructures and its pull can even be felt by the Milky Way

Hydra-Centaurus supercluster

Capricornus supercluster

These two superclusters are the closest neighbours of our own Virgo supercluster and are less than 200 million light years away.

The observable universe surrounding the Milky Way is a patchwork of superclusters and voids. In the direction of the Shapley concentration, there are two other major collections of galaxies. The Coma supercluster is one of the richest and is positioned high above the plane of the Milky Way, enabling us a clear view into its heart. The Hydra-Centaurus cluster is the closest, lying right behind the centre of our galaxy, obscured by bright foreground stars and a cloud of dust.

The structure of the universe

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O

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Sculpture supercluster

The Milky Way is part of the Virgo supercluster, so we are surrounded by other massive collections of galaxies There are a few isolated galaxies in the universe, but the vast majority are bound together in groups. Each of these groups can have as many as 50 members and can span an area measuring several million light years across. Groups with more than 50 galaxies become clusters, either in their own right, or in combination with other neighbouring groups. Some measure tens of millions of light years in diameter. The clusters in turn collect together in vast elongated filaments

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a structure with a gravitational pull so huge that it’s tugging on all of the galaxies in the surrounding area, including the Local Group, and by extension, the Milky Way. Observations of the motion of galaxies in the surrounding area revealed a streaming current of movement in the direction of Centaurus, travelling at a speed of over 1.6 million kilometres (1 million miles) an hour. At the time it was predicted a pull this strong would require an entity containing 1016 times the mass of the Sun. However, as scientists peered through the dust using infrared, microwave and X-ray equipment, it became clear that the Hydra-Centaurus supercluster was nowhere near as massive as originally predicted. Then, several hundred million light years behind it, the even more massive Shapley supercluster came into view.

Virgo supercluster Local Group

Perseus-Pisces supercluster

and large superclusters, bound by their own mutual gravity. Between them are cosmic voids, empty spaces containing just a tenth of the total matter density. Shapley is the largest supercluster in the observable universe, but incredibly it too is dwarfed by something even more massive. The Hercules-Corona Borealis Great Wall is a filament (a galactic superstructure) measuring more than 10 billion light years in length and 900 million light years thick.

Hydra

0

O

Columba supercluster

Horologium supercluster

The Shapley supercluster 180

O

A3566 A3553

A3571 A3570

A3575

A3532 A3530

A3564 A3555 A3559 A1736

A3578

A3528

Shapley supercluster

A3537

A1644 A3581

A1836

A1631

A3574 A3565

Centaurus supercluster

A3526 A1060

Virgo Milky Way

A1367

90

A1656

O

Coma supercluster

With over 3,000 galaxies, and at around 300 million light years from Earth, the Coma supercluster is one of the richest clusters in nearby space.

O

Ursa Major supercluster

Leo supercluster

Sextans supercluster

10,000

The number of Milky Ways that would match the mass of the Shapley supercluster

8,000 The minimum number of galaxies in the Shapley concentration

Coma supercluster

90

By the numbers

Boötes supercluster

Shapley supercluster

The Shapley Supercluster lies much farther away, at around 500 million light years but is many times more massive.

500 million

35

The approximate distance in light years to the Shapley concentration from Earth

25 The number of major galaxy clusters that make up the Shapley supercluster

The core of Shapley is this many degrees in total length

The total number of clusters that make up the main core of Shapley 123

Deep Space

A look inside the galactic supercluster This massive accumulation of galaxies provides a superb chance for astronomers to watch as individual clusters collide The superstructures that make up the universe began to form early in its history, so as matter clustered together gravity took control, adding layer upon layer of complexity. Structures formed from the bottom up, starting small and gradually coalescing to form superclusters, like Shapley. The core of the this huge concentration is marked by a dense string of five interacting galaxy clusters. They are bound to one

another by gravity, and are like filaments described as Fingers of God. The three largest members are all listed in the Abell catalogue alongside some of the most-densely populated galaxy clusters in observable space. Like other rich clusters, these three each have a concentrated central core, containing older elliptical and lenticular galaxies, filled with ageing orange and red stars. Around the edges are the more-structured spiral

galaxies, containing young, hot, blue and white stars. This central strip of interacting clusters offers an opportunity to observe the interactions at the heart of a supercluster on an unprecedented scale. As galaxy clusters merge, they release huge amounts of energy and when viewed in the X-ray spectrum, bright points are visible at the centres. The two very largest clusters, A3558 and A3528, are the brightest visible

Shapley - under the microscope

Poor clusters

What lies within this enormous cosmic body This 2013 image of the Shapley supercluster is a composite created using three separate sky surveys. The galaxies that make up the supercluster are shown in visible light, captured as part of the ESO Digitized Sky Survey. The hot gas that surrounds the clusters is revealed by the Planck space observatory, shown here as a blue cloud. It represents the fluctuations in the cosmic microwave background caused by the gas. As the clusters collide, they release X-rays, shown as pink hotspots.

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here, but each is in a different stage of its lifecycle. At the core of a supercluster, galaxy clusters become trapped in a mutual gravitational dance, so eventually members begin to collide with one another. In the region surrounding cluster A3558 the chain is fragmented and emissions are split into numerous distinct clumps. It’s thought that at some point in the past, a smaller galaxy cluster struck the A3558 cluster

Beyond the cluster core Behind the main core of the supercluster, there is a region of space with no galaxies at all, but extending out to the sides are tens of other interacting clusters.

Merging groups

Within the core of the supercluster, there are groups of galaxies in the process of merging with the dominant clusters.

Two smaller interacting galaxy clusters make up the central portion of the chain, which forms the core of the supercluster.

The Shapley supercluster and the two underwent a dramatic merger, producing shockwaves that rippled through the galaxies. In contrast, A3528 is much less broken up. It’s similar in size and scale to A3558, but the galaxies are arranged into far fewer groups. There are four major clumps, organized into two interacting pairs, each on an eventual course for collision. Around this central core, there are tens of other rich Abell clusters, but identifying the limits of the superstructure has been difficult, so some scientists suspect it extends much further into space than we can see currently, connected by thin filaments of galaxies and gas. The Shapley concentration is still changing as intergalactic winds move through the supercluster, channelling matter towards its core, so the future of the structure is unknown. Its elongated shape could represent the

seed of a new filament, a long thread that will continue to extend outwards into space. Alternatively, the clusters might continue to collapse, drawing in more galaxies from the edges. Either way, the Shapley concentration is truly massive and even today has a measurable affect on its surroundings. The combined gravitational pull of a supercluster is intense, so the effects can be observed over vast distances. The supercluster is even located behind the proposed location of the Great Attractor, an as-yet-unidentified entity of unprecedented scale, responsible for the streaming flow of galaxies in the direction of Centaurus. As astronomers continue to unravel the mystery of the Great Attractor, interest in the Shapley concentration is growing, so more-powerful instruments will enable us to probe even deeper into its heart.

“It extends much farther into space than we can see”

Astrophysicist Donald Lynden-Bell and team tracked the flow of 400 galaxies

The Great Attractor

Is something really pulling us towards Centaurus? When in 1929 Edwin Hubble demonstrated that the universe is expanding, he presented the idea that galaxies expand away from one another uniformly, like raisins in an infinite rising loaf of bread. However, this Hubble flow theory is distorted by gravitational attraction, so peculiar motions appear as passing galaxies interact. This diverts their course and enables them to group together in cosmic clusters. In 1988 English astrophysicist Donald Lynden-Bell and a team of astronomers completed an all-sky survey of 400 elliptical galaxies – they

found there was a serious deviation in their expected flow. Several galaxy clusters in the region of Centaurus appeared to be circling an invisible drain, moving towards an apparently great mass at a speed of several hundred kilometres per second. Dubbed the Great Attractor, the source of the pull is still unknown. Some scientists argue that it’s evidence of a multiverse, while others believe that part of the pull comes from the Shapley supercluster. Others even contest the galaxy flow data entirely, suggesting that it’s little more than noise.

Abell 3558

Also known as Shapley 8, Abell 3558 is the largest cluster in the Shapley concentration and is extremely rich in many galaxies.

Abell 3556

This cluster marks the outer edge of the core and is joined to the centre by a filament described as the Finger of God.

Cluster chain

Five galaxy clusters dominate the core of the Shapley concentration. Three of these, Abell 3558, Abell 3562 and Abell 3556 are described as rich and contain several thousand galaxies each.

This image of A3558 was captured as part of the ESO Digitized Sky Survey

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Deep Space

Observing the Shapley supercluster The largest collection of galaxies in the observable universe has been probed in multiple wavelengths

The Shapley supercluster was first observed in 1930 by Harlow Shapley, an astronomer working at Harvard University. He identified the structure in photographic plates obtained from the Bruce telescope in South Africa, describing it as “a cloud of galaxies in Centaurus that appears to be one of the most populous yet discovered”. Amazingly, Shapley wasn’t even looking at the entire supercluster – what he saw was the faint, elongated cloud of its densely clustered core. By the 1970s, X-ray emissions had been detected in Shapley 8, or A3558, the largest of the clusters. By 1989, several groups were searching for the Great Attractor, an enormous mass theorised to be located in the direction of Centaurus. The UK Schmidt telescope was one of the first to capture clear images of the bulk of the Shapley concentration, revealing the enormous density of galaxies in this distant region of space. The Shapley supercluster lies in a part of the sky known as the Zone of Avoidance, a region almost

entirely obscured by the dust, gas and stars that make up the centre of the Milky Way. This makes it challenging to image, but by using X-ray equipment astronomers are able to peer through the haze. The Clusters in the Zone of Avoidance (CIZA) project aimed to map the galaxies in this obscured area of the sky, hoping to reveal the identity of the Great Attractor. However, when they looked at the Hydra-Centaurus supercluster, it was much less massive than had been predicted. The Norma cluster, once thought to be the source of the Great Attractor’s pull, contained just a tenth of the anticipated mass. However, far behind this cluster of galaxies, the full extent of the Shapley concentration started to become clearer and attentions turned to this enormous supercluster as the potential source of at least part of the attractive force detected. The hot gas that shrouds the galaxy cluster structures like Shapley contains high-energy electrons that distort the microwave background, showing up as hot spots. In 2013, ESA’s Planck The Cartwheel galaxy lies 500 million light years away and was first spotted by the UK Schmidt telescope

Observing closer superclusters, like thexxxxxxxxx xxxxxxxxx Coma cluster, can reveal clues about how the Shapley supercluster evolved xxxxxxxxxxx

A view towards the 'Great Attractor', the gravitational anomaly drawing us into it

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space observatory released the most detailed image ever created of the cosmic microwave background radiation. In this all-sky map showing the last remnants of the Big Bang, the enormous Shapley concentration distorts the signal. The outline of its dense core can also clearly be seen – this is known as the Sunyaev–Zel’dovich effect. It’s possible that the Shapley supercluster extends further into space than we can currently resolve, and that there may even be a much larger structure behind it. NASA’s James Webb Space Telescope, due to launch in 2018 in collaboration with the ESA and the CSA, will be equipped with extremely sensitive infrared equipment, so will be able to look farther than ever before in the direction of the Great Attractor and the Shapley concentration. One of its core objectives is to study the assembly of galaxies and the information that it will reveal about the structure of superclusters like Shapley will be invaluable in advancing our understanding of the structure of the universe.

The Shapley supercluster

UK Schmidt telescope Schmidt telescopes were developed in 1930 by Bernhard Schmidt and are designed around a spherical primary mirror. These kinds of mirrors are very easy to make, and offer a wide field of view, but they suffer from spherical aberration. This means, in order to properly focus the light onto a photographic plate, Schmidt added a correcting lens to bend its path as it entered the telescope. The UK Schmidt telescope is located at the Siding Spring Observatory in Australia and was previously used purely for optical survey data – including the survey that picked up the Shapley supercluster in 1989. Recently the device has been fitted with a fibre-optic instrument, taking advantage of its advanced optics to perform detailed surveys of galaxy redshift.

Corrector lens

Light enters the telescope through a 1.2-metre (3.9-foot) corrector lens, which bends the light, correcting for the shape of the mirror and enabling the light to be properly focused.

Wide field

The UK Schmidt telescope takes images of a sixdegree by sixdegree slice of sky, providing a wide-field view.

Main mirror

The main mirror is concave and measures 1.8 metres (5.9 feet) in diameter. Concave mirrors suffer from spherical aberration – they don’t naturally reflect all of the light back onto a single point.

Plate holder

© Getty Images; NASA; Sayo Studio; Adam Evans; Hewholooks; Andrew Z. Colvin; 2MASS; ESA; JPLCaltech;UCLA; Bill Schoening; Vanessa Harvey; REU program; NOAO; AURA; NSF; Hubble; Scott AnttilaAnttler;

The original photographic plates have now been replaced by fibreoptic spectrograph equipment, used to rapidly measure galaxy redshift.

Camera only

The UK Schmidt telescope is a camera and does not enable an observer to look directly at the sky. Instead, the images are caught as individual photograph stills.

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Space Science

The nuts and bolts behind our knowledge of how the universe works 130 What if the Moon exploded?

We look at the most mind bending hypothetical scenarios

140 A beginner’s guide to spacetime Get to grips with light speed and time travel

148 Do we live in a multiverse?

Is our universe one among many in a potentially infinite multiverse?

150 What is the shape of space?

How geometry can show us the creation and future of the universe

152 How to build a galaxy

Put together the pieces for building a galaxy

“The black hole at the centre of the Milky Way is four million-times more massive than the Sun”

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Build a galaxy 128

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What if the Moon exploded?

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A beginner’s guide to spacetime

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Do we live in a multiverse?

150

What shape is space?

©NASA, Wiki Commons, Adrian Mann

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E H T F I WHAT

N O MO ODED? L P s n o i X t s e End 19 other cosmic qu

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ending -b d in m t s o m look at the r Solar System, a s e k a t e c a All About Spscenarios from across ou rse hypothetical tion and the deeper unive space explora

Key Space exploration Solar System Deep space

INTERVIEWBIO Dr Paul Spudis

Dr Spudis is a lunar geologist for the Lunar and Planetary Institute at NASA. He is an advocate of using the Moon as an exploration port to the rest of the Solar System. In his prosperous time at NASA he has, among other projects, worked on the Lunar Reconnaissance Orbiter mission.

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“First of all, how would the Moon explode? It might disintegrate due to a giant impact, such as a head-on collision of sufficient energy to break up the Moon. “A condition of the produced debris would depend on the conditions of impact, a high-velocity impact would mean lots of vapour, which would then rapidly re-condense into billions of cooled droplets of glass. A low velocity collision would include large fragments tens to hundreds of kilometres in size and much of the debris would melt. “The debris circling the Earth at lunar distance would not be stable, most of it would wander off into solar orbit, while some of it would stay in orbit around the Earth and re-accrete into a larger body. If the Moon exploded into small pieces, it's possible that over time they would form a ring around Earth, much like Saturn has today

This would occur on time-scales of hundreds of thousands to millions of years. “Without the mass of the Moon, lunar tides would no longer exist. However, the Earth and its oceans would still experience tides caused by the Sun. They would be of a much lower magnitude, but would still occur twice per day. There would be an immediate mass extinction of some organisms as intertidal species that depend on alternating periods of high and low tide would struggle to survive and adjust to the much smaller solar tides. “The missing Moon would result in spin axis instabilities for the Earth and the obliquity (the angle from the path of the Sun in the sky) would oscillate wildly."

What if the Moon exploded?

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Space Science

3

Jupiter may have acted like a wrecking ball in the early Solar System, clearing a path for Earth to form

WHAT IF

…the Sun disappeared? If the Sun suddenly disappeared, we wouldn't notice on Earth for 8.5 minutes, until the last of its light reached us. The Moon and the planets, if they were visible, would soon go dark as well, as a wave of darkness - an absence of sunlight - reached them. Within days, Earth would be roughly 100 degrees below freezing, while the atmosphere would freeze and fall to the ground. Exposed to the harshness of space and without the Sun as an anchor, our now surely lifeless planet would be left to drift aimlessly out of the Solar System, along with the rest of our neighbours.

2 ...Jupiter didn’t exist? WHAT IF

INTERVIEWBIO Dr Lisa Kaltenegger

Dr Kaltenegger is a professor of astronomy at Cornell University and also director of the Carl Sagan Institute, a research team searching for habitable planets like Earth beyond our Solar System. Her research focuses on the atmospheres of rocky planets and super-Earths in habitable zones.

“If Jupiter never existed, life on Earth still would still have happened. If there had been heavier bombardment early on then maybe it would have started later, or there could have been more dinosaurerasing impacts, but the jury on that is still out. “People argued for a long time that no Jupiter would be a problem because we would have been hit by way more asteroids. But recent work

WHAT IF

4 …two supermassive black holes collided?

Thanks to simulations, we can make a pretty good guess. In seven years, we'll actually get to observe this happen when two suspected black holes merge into one. For two black holes to collide, they'll need to already be orbiting pretty close to each other inside a quasar, which is a superheated region of swirling dust and gas. Inside, their gravity carves out a cavity in the surrounding disc, with streams of material feeding the black holes. As they get closer to each other,

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these streams actually weaken, a clear sign that a merger is about to happen. In addition, jets of radiation from the poles of the two black holes will merge into one jet. What happens at the point of merging is not known, although it's likely they'd produce noticeable ripples in space-time. After they have merged, the amount of material being eaten by the black holes increases again, causing aftermath radiation – a sign the merge is complete.

has shown that Jupiter also deflects asteroids, so they crash into Earth when otherwise they would not have. So it seems it does not make that much of a difference. “An interesting point in formation is the idea that our Solar System looks like it does because we had Jupiter and Saturn. They basically moved a bit in distance to the Sun during their formation, but not too much and therefore sheltered the inner planets.

“If a big gas giant migrates inward, we find a lot of them close to their stars, so they must have somehow managed to migrate toward it. They cannot be built there and it would destabilise the small rocky planets in that system because of its gravitational pull when it passed by. However, such rocky planets could have formed much later on, after the big gas planets had already migrated inward from the outer Solar System.”

What if the Moon exploded?

the ice on 5 …all Mars melted? WHAT IF

If you think Mars is a barren, dry world, think again. At its poles, Mars has huge amounts of ice, while at lower latitudes, glaciers survive buried beneath the surface. Recent estimates suggested that there are more than 150 billion cubic metres (5,297 trillion cubic feet) of ice on Mars, enough to cover the entire surface with 1.1 metres (3.6 feet) of ice. One reason we don't see water on Mars today is that it has only a very

thin atmosphere. Any water that does make it to the surface quickly boils away, owing to the low atmospheric pressure. But if all the ice on Mars were to melt, some theories suggest that it could kick-start a greenhouse effect that would thicken the Martian atmosphere immensely. If this happened, known as terraforming, it could become possible that water would exist as liquid on the surface. Mars isn't perfectly flat, there

6

WHAT IF …Earth stopped spinning?

For anyone not living at the North or South Pole, are large craters and the first thing they'd notice would be supersonic canyons, so the water winds, as the ground stopped but the atmosphere would pool in certain continued to rotate at 1,770 kilometres (1,100 miles) per areas creating lakes, seas hour. According to NASA, anything not attached to and maybe even bedrock would be scoured clean. The resultant an ocean in the waves would decimate every east-facing shore. northern hemisphere. Assuming Earth was now tidally locked to With no plant life on the the Sun, the remaining life on the surface, this water wouldn't planet would have perpetual kick-start a new era of vegetation. light or darkness. However, it would provide a handy resource for humans.

2. Thicker atmosphere As the ice melts, the water would evaporate, but this could thicken the Martian atmosphere, letting water remain on the surface.

3. Oceans

The largest body of water would be in the northern hemisphere, which was once thought to be an ocean billions of years ago.

1. Icy poles

Mars has enough ice at its poles and under its surface to cover the planet in 1.1m (3.6ft) of water if it all melted.

4. Clouds and rain

Eventually all that water vapour might start to form clouds above the surface of Mars.

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8 IF

xxxxxxxxxxxxx Space Science

7

WHAT

...a star near Earth went supernova?

WHAT IF

…we poured a giant bucket of water over the Sun? If you pour water on a fire here on Earth, it will be extinguished. But the thing to note about the Sun is that it is not burning in the same way a regular fire burns. Instead, it is undergoing nuclear fusion and turning hydrogen into helium, which gives it its heat. Water is composed of hydrogen and oxygen. Therefore, pouring a giant bucket of water on the Sun isn't going to extinguish it, instead it will cause it to burn much faster and brighter than it already does. If you had an infinite supply of water, the Sun would start to go through some bizarre stages. One

of these is known as a helium flash, when the amount of helium on the Sun becomes so overwhelmingly intense that a runaway fusion of helium begins to occur. The ultimate result of continuing to pour water on the Sun is that, eventually, its mass will become so great that it will collapse in on itself and form a black hole. It's possible that before this stage it would expel its now huge outer layers, likely enveloping most of the planets in the Solar System and leaving our charred remain of a planet orbiting what will eventually become a supermassive black hole.

"Pouring a giant bucket of water on the Sun isn't going to extinguish it, instead, it will cause it to burn much faster and brighter" Pouring enough water on the Sun would cause it to expand from a yellow dwarf into a red giant, before it collapsed into a black hole

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For a star to destroy life on Earth, it would have to be less than 50 light years away. Fortunately for us, there is no star in that range that could go supernova. But if one did, the resultant X-rays and gamma rays would destroy our ozone layer and biosphere, subjecting us to intense ultraviolet rays from the Sun. Such an event would also ionise nitrogen and oxygen in the atmosphere, causing extremely poisonous nitrogen dioxide to form, killing most of the life on our planet.

What if the Moon exploded?

9

10 IF

WHAT IF

…Earth was twice as big?

According to Dr Scott Kenyon from the Centre for Astrophysics (CfA) at Harvard, if Earth were to become twice as massive, it would lose its molten heat from its early years more slowly. “The atmosphere is denser and everything is heavier and requires more energy to move around,” he said.

In this scenario, while ants and snakes would be happy, birds might be rare and humans would be shorter and slower. “We would probably know more about the oceans and less about the stars," he added. “Our buildings would be less majestic. But projectiles would require more energy to go less far, so there wouldn't be many wars.

WHAT

…space was full of air? Assuming this air-filled universe was somehow able to remain stable, you'd Dr Dimitar Sasselov of hear the Sun and nothing else, not even your own the CfA took a different thoughts. At Earth's distance, the Sun would deliver stance: If the Earth was around 100 to 125 decibels of noise. That’s bordering twice as big, its mass would on the levels that cause physical pain. For any be eight times greater “It extraterrestrial races orbiting larger stars, it would would be tough to walk be much louder and likely cause intense pain, around but it would be a good if not death. As for the universe, it would excuse to spend time on the collapse in on itself fairly quickly as beach... you're lighter in water!” the matter would be all over the place.

What a 100kg person weighs on other worlds Sun

Mercury

Venus

Moon

Mars

Phobos

2707.2kg

38.7kg

90.7kg

16.6kg

37.7kg

0.0602kg

Jupiter

Gannymede

Europa

Io

236.4kg

14.48kg

13.35kg

18.35kg

Callisto

Saturn

Titan

12.64kg

106.4kg

11.9kg

Uranus

Neptune

Pluto

88.9kg

112.5kg

6.7kg

Earth 100kg

Earth x2

1970kg

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Space Science

11

WHAT IF

…an astronaut floats off in space?

During a spacewalk on the ISS, astronauts always work in pairs. Each has two safety tethers to stay attached to the station, in addition to numerous handrails to cling on to. If these tethers failed and they became detached, the astronauts have a redundancy system – the Simplified Aid for EVA Rescue, or SAFER. It is worn like a backpack and uses 24 small jet thrusters to let an astronaut move around in space. “If an astronaut were to become untethered and float away, SAFER would help him or her fly back to the spacecraft,” a NASA Spokesperson told All About Space. But we know you're wondering, what if all that fails? Well, that's where things get a bit hairy. If an astronaut floated off from the station and for some

12 IF

reason the other astronaut couldn't save them, it's possible that the astronauts on the ISS could pilot a Soyuz and pick them up. They wouldn't be able to open the hatch of the Soyuz though, as they wouldn't have time to go through the depressurisation routine, so the astronaut would have to cling on to the side. They must also steer clear of the peroxide thrusters on the side of the Soyuz, which could damage their suit or blast them off into space. When safely dragged back to the station, they could re-enter through the airlock they left from, while the Soyuz returned to dock. Whether such a manoeuvre is safe, or plausible, is something that NASA and the other space agencies hope they never need to find out.

WHAT

…what if an astronaut took off their helmet in space? Contrary to what many movies have portrayed, the astronaut wouldn't immediately suffocate or explode. It would take about 15 seconds for your body to use up its oxygen reserves and if you didn't hold your breath, you could survive anywhere up to two minutes. But during this time the water in your body would completely vaporise and the liquid on your tongue would start to boil.

WHAT IF

13 …the ISS had to be evacuated?

Disaster has struck! A meteor has critically damaged the ISS and the crew must immediately evacuate. What happens? With two three-seater Soyuz spacecraft docked to the station, the entire crew of six can always return

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home. The crew will need to quickly don their re-entry suits and take their places in the Soyuz spacecraft. Each Soyuz can be separated in three minutes and the time from deciding to leave to landing on Earth is about 3.5 hours in total.

However, the ISS would not be lost. It was always designed to operate unmanned if needed, so it could be placed into Assured Safe Crew Return (ASCR) mode, until another crew could be sent. However, without a crew there, it could fall into disrepair.

The safety tethers attaching the astronauts to the ISS can be seen in this picture

What if the Moon exploded?

14 IF

WHAT

…Apollo wasn't cancelled?

During the Apollo programme, many were convinced that the next logical step was to go to Mars. Indeed, at the time NASA had already begun developing a nuclear engine called NERVA (Nuclear Engine for Rocket Vehicle Application), widely viewed as necessary for a Mars mission. But by 1972 the final three Apollo missions: Apollo 18,19 and 20, had been scrapped and so too had NERVA, with NASA instead focusing on the Skylab space station, the Space Shuttle and ultimately the ISS. Some experts believe, had this not happened, that humans could have already built a permanent base on the Moon.

WHAT IF

15 …NASA had an unlimited budget? “I see NASA’s mission as nothing less than to ensure the survival of humanity. Let's start there. That means understanding Earth, protecting it and extending humanity beyond it, in case something goes wrong with the first two! “To understand Earth, I’d deploy a large constellation of satellites looking back at Earth with high-resolution

cameras and sensors that provide global coverage 24 hours a day, seven days a week. Data would be accessible directly by the public via the free high-speed internet built into the system. Anyone could access the pictures/data with a host of analysis overlays from their phone, whether looking for a lost child or determining if their crops need water. “To protect Earth, I’d immediately deploy another constellation of spacecraft throughout the Solar System for the early detection and tracking of comets and asteroids. Those are the threats from beyond

Earth that we could actually do something about. “To extend humanity, I’d invest a large amount in technology for automation, resource utilisation, long duration propellant storage and transfer, space-based manufacturing, radiation-free power and advanced propulsion. We would have to also to invest in sustainable Earth-toorbit capability, first with partially reusable rockets, then someday, when technology and politics permit, a space elevator. NASA would then look to pioneer settlements on the Moon and Mars."

INTERVIEWBIO Dr Patrick Troutman

Dr Troutman is a senior technologist at the NASA Langley Research Center in Hampton, Virginia. He is currently leading the integration of the NASA Evolvable Mars Campaign (EMC), a strategic analysis to develop options for human space exploration.

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Space Science

16 …we found life? WHAT IF

INTERVIEWBIO Dr Seth Shostak

Dr Shostak is the senior astronomer and director of the Center for SETI (Search for Extraterrestrial Intelligence) Research. He is a strong advocate for finding out if we are alone in the universe and has been responsible for boosting the profile of SETI.

“Many people feel discovering cosmic company would be so disruptive that government agencies would keep the news secret. The public, it’s assumed, is not adult enough to hear such things. “While that scenario plays well with those inclined to believe in conspiracy, the truth is different and demonstrated. A few false SETI alarms have shown us what really happens. The initial reaction would be a rise in the adrenaline level of the scientists involved. They would spend days frantically confirming

17 IF

that the transmission is really coming from ET. During this time the media will be all over the story, wanting to know whether the detection is real or not. The government, for its part, has never really shown any interest in such signals. “If we could prove that the discovery was the real deal, then there would be a press conference to announce what we know. Of course, by then all the media will have been running the story for days. “In the case of the discovery of less imposing life – for example, pond

WHAT

scum under the rusty landscapes of Mars or beneath the ice of a moon of Jupiter – the scenario would scarcely be different. In both cases, there’s no plan to keep secrets. A discovery would simply be a very big story and the public would want to know more. “In either case, we would learn that life is commonplace in the cosmos. If we were to pick up a radio signal, we’d also know that intelligence is not limited to Homo sapiens. We would finally be able to establish our place in the biological scheme of things.” Governments have never shown a particular interest in the potential discoveries of alien life

…a deadly asteroid threatened Earth? There are many proposals to deflect an incoming asteroid. These include detonating nuclear weapons on it to divert its path or using a spacecraft to push it out of the way. But none of these methods are ready to launch. If a killer asteroid was heading our way, we'd probably know about it years or decades in advance as NASA and other agencies are pretty good at tracking large objects. But if it was discovered late, with impact only a week away for example, then we're afraid you'd have to prepare for the worst. This is why many groups want to quickly improve our defences.

WHAT IF

18 …Earth was closer to the centre of our galaxy? INTERVIEWBIO Dr Steve Howell

Dr Howell is one of NASA's leading exoplanet experts, having been the project scientist for the hugely successful Kepler mission, which has found thousands of planets in the galaxy.

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“If the Sun were located much nearer to the centre of the Milky Way, things would be a bit different for us humans as we orbit here on Earth. The Milky Way would be far brighter and wider in extent in the sky and would display large extended regions of dark dust patches and glowing clouds of gas surrounding newly formed stars, especially as we peer toward to the galactic centre. “The sky would be filled with hoards of young, bright stars, many

of which would be easily seen in the daytime. Looking toward Sagittarius A, the 4 million solar mass black hole residing in the centre of the galaxy, we would easily detect motion of the stars over time as they orbit the black hole every 15 to 20 years. “The number of stars nearby to the Sun would be far greater than now and some might come close enough to affect the orbits of the planets in our Solar System, perhaps making the orbits become increasingly elliptical.

“If the orbit of the Earth became significantly elliptical, seasonal changes would depend less on the tilt and far more on the changing distance Earth would be from the Sun. Winters would become much colder and summers far hotter in such a case. “Occasional close encounters might drive many more comets into the inner Solar System, increasing the chance of impacts and even allowing planets to interact.”

What if the Moon exploded?

universe wasn’t 19 …the expanding? WHAT IF

Expansion

In actuality the universe is expanding, so the amount of light we see is limited.

Paradox

20IF

According to Olbers' paradox, if stars were evenly distributed we would see them across all points of the night sky.

WHAT Light

As we look further and further into the universe, we would see more and more stars, making the night sky brighter.

…there was no gravity?

If there was no gravity since the beginning of time, then simply put, there would be no universe. Without gravity, none of the matter in the universe would have been able to coalesce together into objects like stars and galaxies and perhaps the Big Bang would not have even happened at all. Alternatively, if gravity were ever-present until, say, right now, then everything as we know it would begin to drift apart. Not a pretty sight.

You are here

Our Solar System is at an ideal distance of 26,000 light years from the Milky Way’s centre.

Some have suggested our planet orbits in a galactic habitable zone and whether life could survive closer to the centre is currently unknown

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© NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring; NASA/ Daein Ballard; NASA/JPL/Space Science Institute; ESO; Sayo Studio; Tobias Roestch; Alamy; Science Photo Library; Lisa Kaltenegger

If the universe wasn't expanding, one thing that would be immediately noticeable is that the night sky would be a lot brighter. In 1823 German amateur astronomer Heinrich Wilhelm Olbers pondered the following: if the universe was infinite and static, then the night sky should appear bright, as the light from an infinite number of stars reaches Earth. Of course, as we now know, space is expanding, this problem, known as Olbers' Paradox, is not the case. If the universe had started in its present state, then we wouldn't see redshift from distant galaxies and the shifting of their light toward one end of the spectrum. In the long term, it's possible that gravity would pull everything in the universe toward each other, perhaps culminating in a ‘Big Crunch’, the opposite of the Big Bang.

A beginner’s guide

Get to grips with light speed and time travel with our back-to-basics guide to Einstein’s universe

Understanding how and why planets and other objects move through space has been one of astronomy’s greatest challenges, an apparently never-ending quest that began when the first stargazers noticed the planets and Moon moved in a different way to the fixed stars. This was only resolved in the early 20th century. Along the way, the mystery of planetary orbits inspired great advances in mathematics, observation techniques and cosmology. At either end of the 1600s, two great advances seemed to offer a solution. First, Johannes Kepler’s laws of planetary motion described how objects

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move on elliptical orbits, and that their speed of motion depends on their distance from the body they orbit. Then, in 1687, Isaac Newton published his generalised laws of motion and universal gravitation, explaining how Kepler’s laws and gravity on Earth could arise from the action of a universal force of gravity between objects with mass. Newton’s laws turned out to be accurate in the vast majority of everyday situations, but in the late 19th century, astronomers and physicists grew increasingly concerned about several unresolved problems. These ranged from the apparently simple (why doesn’t Mercury’s orbit behave in the way

predicted by Newton’s laws?) to the more abstract (why doesn’t the speed of light reaching an observer on Earth vary when the light source is moving towards or away from us?). By the early 1900s, many scientists recognised that physics was facing a crisis – but only one man, Albert Einstein, had the nerve to suggest a radical solution. Einstein’s theories of special and general relativity, published in 1905 and 1915 respectively, rewrote the laws of physics from the ground up, inventing the concept of spacetime and paving the way for a bizarre new universe of black holes, warped space and, perhaps, even time travel.

A beginner’s guide to spacetime

Jargon buster Gravitational well

Exotic matter

Thought experiment

Singularity

Event horizon

A model to illustrate a body's gravitational field strength. Deeper wells mean stronger gravity, therefore more energy is needed to escape them.

Matter that doesn’t behave as we expect ‘normal’ matter to, such as dark matter and hypothetical particles with negative mass.

A method of speculating on potential consequences. Generally used when it is not possible or feasible to carry out the real experiment.

A point in spacetime where gravitational forces become infinite and the laws of physics as we know them break down.

An invisible, calculable boundary surrounding a black hole. Anything that passes the event horizon will not escape, not even light.

Reference frame

Precession

(Non-)Inertial

Frame dragging

White hole

A perspective used to observe motion. Fixed frames are stationary, whereas moving frames travel with the object being observed.

The gradual change in orientation of a planet or a moon’s rotational axis, similar to the way a spinning top wobbles as it spins.

Used to describe reference frames. An inertial frame has a constant velocity, in a noninertial reference frame there is acceleration.

The effect that a rotating body has on spacetime. Massive bodies such as black holes can twist spacetime as they spin.

The hypothetical opposite of a black hole: nothing can enter the white hole from the outside, but matter and light can escape.

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Space Science

What is relativity?

Einstein’s theories of relativity were mostly aimed at addressing the problem of the fixed speed of light. Since the mid-19th century, astronomers understood that the speed of light moving through air was just under 299,800 kilometres (186,287 miles) per second. There had been many attempts to detect variations in this speed and this, scientists hoped, might confirm the presence of the luminiferous aether, a hypothetical substance thought to pervade the universe and act as the carrier medium for light waves. But a crisis in Newtonian physics was sharply highlighted in 1887, when the MichelsonMorley experiment, a laboratory test that should have revealed the aether’s effect on light rays moving in different directions, drew a blank. Einstein’s approach was radical. While others tried to find ways around the problem, he tackled it headon by asking what if the aether did not exist? In a series of thought experiments, he made only two assumptions: that the laws of physics are identical for all observers in inertial situations and that there

Mass increases with speed Setting the speed of light as a universal speed limit led Einstein to his remarkable discovery that mass and energy are equivalent. He arrived at this by considering what would happen if an object travelling at relativistic speed continued to pour energy into acceleration. The energy could be provided internally, for instance on a rocket powered by an ion engine, or externally, for example in a particle accelerator. Einstein realised that in either case, the object’s kinetic energy would have to increase even if its velocity could not. Since kinetic energy is reliant on both mass and velocity, this indicated that adding energy to an object moving at near-light speed tends to increase its mass. In fact, Einstein found that the energy content of an object is equal to its mass times the speed of light, c, squared: E=mc2.

10kg Mass at 0 per cent speed of light

Special relativity elegantly solved many of the problems of turn-of-the-century physics, and successfully predicted a variety of strange phenomena that astronomers have since observed and measured (see over). In the next decade, Einstein tackled the far harder problem of how they applied in situations involving acceleration. He was aided by his former tutor Hermann Minkowski’s development of the concept that we now call spacetime – the idea that the familiar three independent dimensions of space and one of time are not as fixed as we think. In 1915, Einstein finally unveiled his theory of general relativity: the maths was much more complicated, but general relativity’s central breakthrough was equally simple and brilliant: Einstein realised that being in a gravitational field was exactly the same as experiencing uniform acceleration, so the effects of gravity should mirror those of acceleration. This led him to conclude that the phenomenon we experience as gravity is in fact a distortion of spacetime itself, created by the presence of mass.

E=mc

2

Einstein’s equation explained

Einstein’s investigation of the way that mass increases as an object attempts to accelerate near the speed of light (see ‘Mass increases with speed’ boxout) revealed this simple but elegant equation that lies at the heart of all modern physics. Here, E is a body’s energy content, m its mass and c the speed of light, a universal constant. It can be used to compare a body’s rest mass and energy (excluding energy due to motion), or its total relativistic mass and energy (including energy due to motion).

The idea that mass and energy are interchangeable in extreme circumstances lies at the heart of modern physics – it explains the power source of stars, where nuclear fusion of light elements into heavier ones converts a small excess of mass directly into energy; and the origins of matter in the universe itself, where enormous amounts of energy released in the Big Bang coalesced into subatomic particles, which then formed atoms.

100kg Mass at 99.5 per cent speed of light

However much energy you apply to it, it is simply impossible for an object with any mass to achieve the speed of light

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is no aether. Instead, the speed of light in a vacuum is a constant, unaffected by the motion of the light source. Einstein felt able to abandon the aether because of another important breakthrough. He was the first to marshall the evidence that light travels in photons, self-contained wave packets that require no medium to carry them. Special relativity itself considers the way that the laws of physics would then appear in situations of relative motion at close to the speed of light (what we now call relativistic situations). Using quite simple mathematics, the theory predicts remarkable consequences. From the perspective of a distant observer, objects moving at relativistic speeds appear both to be compressed in their direction of motion and experience a slower passage of time. Einstein also looked further at the energy content of a body in relativistic motion, discovering the most famous equation of all time (see below). He concluded that the speed of light is not only a constant, it’s the ultimate speed limit of the universe.

A thermonuclear hydrogen bomb releases huge amounts of energy in the same process that powers a star: fusion

A beginner’s guide to spacetime

Time dilation The passage of time at different speeds for different objects is predicted by both special and general relativity. In special relativity, time runs more slowly for travellers moving at high, relativistic speeds, while general relativity shows that time also runs more slowly in strong gravitational fields. As with the length contraction, it’s important to understand that both effects are real rather than an illusion seen only by external observers. Intriguingly, the interplay of relativistic and gravitational time dilation means that different spacecraft and travellers around Earth experience different effects.

Astronauts aboard the ISS, for instance, are just a few hundred kilometres from Earth and moving at high speeds because of their low orbit, so they experience a double ‘slowing down’ effect: by the time astronaut Scott Kelly reaches the end of his current year-long ISS mission, he will have aged 0.014 seconds less than his Earthbound twin Mark. GPS satellites, meanwhile, orbit more than 20,000 kilometres (12,427 miles) up and therefore experience much less gravitational time dilation, so even though they are still moving at high speed compared to an Earthbound observer, they actually experience a faster passage of time.

Cosmos 158

Seconds younger: 0.3504s Time in space: 17,567 days

Hubble Space Telescope

Seconds younger: 0.2086s Time in space: 9,186 days

USA-66

Seconds older: 0.3461s Time in space: 8,973 days

Syncom 3

Seconds older: 0.8644 Time in space: 18,555 days

Length contracts with speed One major prediction of special relativity is the shortening of the length of an object travelling at close to light speed. An observer’s perception of any object’s length depends on the locations from which light rays must leave each end, in order to arrive simultaneously in the observer’s eye. If the object is moving at relativistic (very high)

speed, then it may have moved forward significantly by the time light from the closer end has to leave on its journey, so the object will appear shorter. The scientists who discovered this phenomenon viewed it as a sort of illusion but Einstein showed it as a ‘real’ effect of special relativity, while Hermann Minkowski explained it as a distortion of spacetime.

“Scientists viewed this as a sort of illusion”

Stationary

80 per cent speed of light

90 per cent speed of light

Objects travelling near the speed of light become significantly shorter in the direction of travel

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Space Science

Testing Einstein’s universe Einstein himself used general relativity to finally solve the problem of Mercury’s orbit (see ‘Mercury's wobbly orbit’ boxout) but it really only came to worldwide attention in 1919, after British astronomer Arthur Stanley Eddington led an expedition to the island of Príncipe off West Africa to photograph the stars around the Sun during a total solar eclipse. Eddington’s expedition aimed to demonstrate one of Einstein’s most important predictions: gravitational lensing. If gravity is a distortion in spacetime rather than a force that only acts between objects with mass, then strong gravitational fields should affect not only the motion of massive objects, but also the paths of massless light rays passing nearby. The nearest large mass capable of creating a measurable effect is the Sun, but it’s only during a solar eclipse that the stars around it, whose light rays are most affected, can be seen. Eddington’s proof of relativity, an apparent shift in the position of stars close to the Sun from their normal positions, made headlines around the world. But it’s only recently that astronomers have been able to put gravitational lensing to use

Singularities One common way of thinking about spacetime is to imagine the universe as a two-dimensional rubber sheet with stars, planets and other objects sitting on it and creating dents. The heavier and denser an object is, the larger the dent it makes in the surrounding fabric of space and the greater the effect it has on nearby objects. A singularity, which concentrates anything from a few times the mass of the Sun to many millions of times at a single point in space, creates a bottomless pit in spacetime from which nothing can escape.

1. Warped space

All massive objects make distortions or gravitational wells in spacetime – including planet Earth. They can be visualised as dents in a two-dimensional sheet, or ‘pinches’ in three-dimensional space.

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as a tool for observing the distant universe. They can magnify and intensify the light from the most distant galaxies, and also reveal the amount and distribution of matter in foreground objects responsible for the lensing effect. Another practical test of relativity became possible with the beginning of the space age in the Fifties, and the advent of super-accurate atomic clocks, which measure time using the regular pulsations of an atom excited by lasers. By flying atomic clocks on-board jet fighters or spacecraft, while keeping a synchronised clock on the ground, physicists have confirmed on many occasions that time flows more slowly for objects moving at high speeds and those within strong gravitational fields. The most impressive demonstrations of relativity, however, have come from astronomy, with the discovery of objects that can only be explained in Einstein’s terms. The best known of these are the black holes, objects with such extreme gravity that nothing can escape them – not even light. A black hole is a singularity, a tiny point of near-infinite density surrounded by a ‘point of no return’, the

event horizon that seals it off from the surrounding universe. The existence of black holes can only be inferred from principles of subatomic physics and by measuring their effect on nearby visible objects. But they have been confirmed as both stellar-mass objects a few times heavier than our Sun (formed by the collapsing cores of the heaviest stars) and as supermassive monsters with the mass of millions of Suns, lurking at the cores of most galaxies. General relativity predicts that these bizarre objects have an extraordinary effect on their surroundings (see ‘Singularities’ boxout). Other predictions of general relativity have not yet been confirmed. One such effect is frame dragging, first proposed as a consequence of Einstein’s theory by Austrian physicists Josef Lense and Hans Thirring in 1918. This effect creates small distortions in the spacetime around any massive rotating object, and several satellites have attempted to measure it with varying degrees of success. The signs are promising, however, and one intriguing consequence of frame dragging is that it could, theoretically, be used to create a time machine.

2. Safe distance

Despite their fearsome reputation, black holes are not cosmic vacuum cleaners – depending on their mass, they distort the paths of objects in nearby space, but anything moving fast enough can still escape their grasp.

3. Event horizon

Anything that ventures inside this roughly spherical region around the black hole can never escape – not even light. Hence the event horizon keeps the singularity forever hidden from sight.

4. Downward spiral

Objects drawn into a singularity are pulled onto spiral paths rather like crumbs disappearing down a plughole.

A beginner’s guide to spacetime

Gravitational lensing

The lensing effect of Abell 1689, a huge galaxy cluster in the constellation Virgo, distorts the light from background galaxies, warping their images into blue and red arcs

According to general relativity, the gravitational effect of large masses is actually a distortion of the spacetime around them – a gravitational well that deflects the path of anything passing nearby. Light rays passing through the distorted region are moving so fast that they are barely affected, but if an object’s mass is large enough (for example a cluster of galaxies) or they pass very close to a smaller mass, then their paths may be significantly deflected. When these rays arrive at Earth, they produce a distorted image of the object, perhaps not even in the same part of the sky.

Fast fact

The Einstein Cross in the constellation Pegasus is a uniquely perfect example of lensing at work. It consists of a central foreground galaxy surrounded by no fewer than four lensed images of a distant background quasar (the nucleus of an active galaxy)

As an object falls into a black hole, it gets pulled apart due to really strong tidal forces. It would be stretched out in a process called spaghettification until all its atoms are completely ripped apart.

Mercury’s wobbly orbit Mercury’s has the most elliptical orbit of any major planet in the Solar System, ranging between 46 and 70 million kilometres (28.6 and 43.5 million miles) from the Sun. What’s more, its perihelion (the closest point to the Sun) slowly changes its orientation, wobbling – or ‘precessing’ – around the Sun with a 2,258-year cycle. The precession of Mercury was a long-standing problem for Newtonian physics, since while a large element of it can be accounted for by the gravitational pull of other planets in the Solar System, a small but significant proportion cannot be explained in this way. Einstein demonstrated that general relativity could account for the difference through subtle effects on the Sun’s gravitational field, and this has subsequently been confirmed with precise measurements not only of Mercury’s orbital precession, but also of similar wobbles in the orbits of Venus and Earth itself.

Orbit 2

Sun Mercury Orbit 1

Orbit 3

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Time travel & light speed

Relativity describes a universe in which no object with mass can reach the speed of light, but space and time can be warped by extreme masses and high speeds. Two of the most fascinating questions it raises are: whether we can ever overcome that lightspeed limit and whether we might be able to bend the rules of spacetime in order to achieve time travel. In a sense, special relativity makes the answer to both questions simple. The time dilation effect slows down the passage of time for objects moving at relativistic speeds, so if you could travel in a spacecraft at a large fraction of the speed of light, you could travel many light years while experiencing the passage of just a few months; from your own point of view, you would be travelling far faster than the speed of light, while an outside observer would see you travelling at less than the speed of light, but experiencing greatly slowed-down passage of time. What’s more, when you reached your destination and re-established contact with Earth, you might find

that decades had passed on Earth – in effect, you will have experienced one-way time travel into the future. This was the basis of Einstein’s famous twin paradox – the idea that a space-travelling twin might end up much younger than a sibling that remained on Earth. Recently, researchers have suggested other ways of getting around the light-speed barrier without relying on time dilation. One of the first theories of this kind was the Tipler cylinder, initially proposed in 1974 (see ‘The Tipler cylinder’ boxout). A more recent concept is the Alcubierre drive suggested by Mexican theoretical physicist Miguel Alcubierre. This effectively cheats the rules of relativity with a spacecraft that moves at non-relativistic speeds relative to its surroundings, but is itself enclosed in a bubble of flat spacetime that is projected at fasterthan-light speed across the universe, by warping the spacetime around it. The best-known way around the light-speed barrier, however, is to use a wormhole – a

hypothetical spacetime tunnel that offers a much shorter path between two distant regions of spacetime (see ‘Using wormholes’ boxout) and might also offer a way of building a time machine that allowed travel into the past as well as the future. However, time travel into the past raises huge questions about the relationship of cause and effect – it would theoretically make it possible to take actions in the past based to prevent future events, creating a paradox. For this reason and others, many physicists, including Stephen Hawking, doubt that it is possible or believe it must be limited in some way. The wormhole time machine may be one solution to this problem. For the moment, time machines and faster-thanlight drives remain the province of theoretical physicists and science-fiction writers. But the fact that we can even begin to conceive of how such things might practically be achieved is yet another testament to the power of Einstein’s amazing theory.

The Tipler cylinder

Using wormholes

The Tipler cylinder is a hypothetical time machine that some physicists have argued could be built by an advanced civilisation. It consists of a very long, thin, massive cylinder spinning rapidly around its central axis: according to general relativity, such an object would generate an effect known as frame dragging that would distort spacetime around it and allow spacecraft travelling at fairly slow speeds along spiral paths to travel back in time. Using such a cylinder as a time machine was first proposed by cosmologist Frank Tipler in 1974, but others have since expressed their doubts. Stephen Hawking showed, for example, that such a cylinder would need to have infinite length, or be composed of some form of hypothetical exotic matter with negative energy content.

If they exist or could be created, then wormholes could offer a potential shortcut across the universe, bypassing the ultimate cosmic speed limit without breaking it. Wormholes were first identified as a possible consequence of general relativity in 1916 and were thought to arise naturally during the formation of black holes. The essential idea is that each black hole is matched by a corresponding energy-spewing white hole elsewhere in the universe, and because the spacetime of the universe as a whole is warped and folded by the matter within it, this Einstein-Rosen bridge may form a much shorter path between two distant regions. Physicists today understand that the rotation and magnetic fields of black holes make it very hard to form a natural stable wormhole, but it might still be possible for an advanced civilisation to create a stable, traversable wormhole using exotic matter.

Warped universe

In the warped spacetime of the Tipler cylinder, approaching spacecraft that turn away on a curved path travel back into the past

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A wormhole works as a shortcut because spacetime itself is warped and distorted, folding back on itself thanks to the concentrations of mass and energy within it.

A beginner’s guide to spacetime INTERVIEW

Professor Ronald Mallett 

We speak to an expert on time travel and general relativity

Professor Ronald Mallett is a theoretical physicist at the University of Connecticut, specialising in general relativity, quantum gravity (the potential unification of relativity and quantum physics) and time travel. He is best known for proposing a machine, within the capabilities of current technology, that could potentially send particles backwards in time, described in his 2006 book Time Traveler: A Scientist's Personal Mission To Make Time Travel A Reality. Could you briefly describe how your proposed time machine would work? In Newton’s theory only matter can create a gravitational field. By contrast, in Einstein’s theory both light and matter can create gravity. By solving Einstein’s gravitational field equations, I was able to show that a circulating beam of light can cause a twisting of empty space. A simple analogy would be with a cup of coffee. Think of the coffee in the cup as being like empty space and the spoon as being like the circulating light beam. As the spoon stirs the coffee it creates a vortex in the coffee. Similarly, a circulating light beam creates a vortex in empty space. In Einstein’s theory space and time are linked. A further development of my work showed that the vortex in space created by the circulating light could lead to a vortex in time which could allow time travel to the past.

The Alcubierre drive is a hypothetical technology that warps space to achieve faster-than-light travel

Long way around

The distance across normal space between wormhole entry and exit points might be many millions of light years.

Point of entry

A wormhole entrance would resemble a black hole, surrounded by an intense gravitational field creating a field of warped spacetime.

How close do you think you are to developing a working prototype? At this point it is not possible to estimate the completion of a working prototype. A feasibility study would first have to be done, which would have an estimated cost of $250,000 [£164,000]. The feasibility study would determine what technology would be needed for the actual experiments and the total cost – this could easily run into many millions of dollars.

Connecting passage

Exit point

The exit of a wormhole is a hypothetical white hole spewing raw matter and energy into a different part of the universe.

© Corbis; Alamy; NASA; NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring

A narrow spacetime tunnel connects the ends of the wormhole, normally via a singularity. In order to make the tunnel traversable, exotic matter must be used to keep it open and avoid the singularity.

A circulating beam of light could be used to create a vortex in space, allowing time travel to the past

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xxxxxxxxxxxxx Space Science

Do we live in a multiverse?

Big Crunch

Universes that fall back on themselves end in a similar hot, dense state to the Big Bang itself. Some cosmologists speculate that this kind of ‘Big Crunch’ could give rise to another universe in turn.

Cosmologists are fascinated by the idea that our universe is one among many in a potentially infinite ‘multiverse’ – but can we ever know for sure? What exactly is a multiverse? The exact definition depends on which expert you’re talking to and which theory you’re discussing, but in essence, all hypothetical multiverses are structures that can play host to a large – possibly infinite – number of individual, self-contained universes. A universe, in this context, is simply a volume of four-dimensional space-time, within which uniform laws of physics and fundamental constants of nature apply. Our own universe was created in the Big Bang explosion 13.8 billion years ago and has been expanding ever since. The limited speed of light determines the distance of the furthest objects we can see, creating an ‘observable universe’ stretching to about 47 billion light years in every direction from Earth, but most astronomers believe that the universe as a whole stretches far beyond this boundary. Traditionally, the Big Bang is seen as creating not just all matter in the universe, but also space and time themselves. It might seem to prevent the creation of a multiverse, but there are several ways in which our universe could still be just one of many. One possibility lies in the conditions from which the Big Bang arose. Many cosmologists envisage a so-called ‘quantum foam’ out of which the Big Bang spontaneously erupted. If the same foam could give rise to other Big Bangs, then it could produce large numbers of self-contained, isolated universes, each meeting a different fate depending on its precise mix of physical laws and fundamental constants. While universes in such a scenario would be forever undetectable from each other, other possible multiverses could leave a detectable imprint. Since the Eighties astronomers have largely accepted a modification of the Big Bang theory called ‘inflation’, which explains our observable universe as the product of a sudden and dramatic expansion of a tiny portion of the infant universe. Inflation is the only way to create a cosmos with the large-scale features we observe, and may also have helped to determine its physical properties, but some cosmologists have suggested that it might not be a one-off event. Instead, a primordial multiverse might have given rise to an infinite number of inflationary bubbles, each a universe in its own right. The recent discovery of gravitational waves imprinted on the early universe may be an important hint that we live in just this kind of multiverse.

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Big Bang

Universes begin with a Big Bang that may be triggered by a chance fluctuation in the quantum foam (as shown here), or a collision between branes.

Closed universe

However, there are other options. Another possible trigger for the Big Bang is a collision between hypothetical many-dimensional structures known as branes, and if this kind of collision happened once, then it could happen many times to produce many different universes. And then there are even weirder possibilities. The simulated multiverse theory suggests that we might all exist as one of many Matrix-like simulations in an impossibly advanced computer. The quantum multiverse theory, meanwhile, argues that the fuzzy and uncertain events at the subatomic level of matter only create a neatly ordered large-scale cosmos through continuous branching, creating an infinite array of parallel universes in which every possible quantum outcome is played out. Developed in the Fifties, this was the original multiverse theory – it has gained widespread popularity much more recently, but still raises important questions about why we perceive only one universe with a single course of events. Several other theories have been conjured up from the complexities of theoretical physics, but there’s one last theory that’s easily grasped – a cyclic multiverse in which individual universes exist not in parallel, but in series. In this scenario, each new universe arises from the ashes of the previous one, creating a cosmic lineage that extends from the infinite past into the infinite future.

The development of an individual universe is determined by fundamental properties such as the strength of gravity and the amount of matter contained within it. If gravity overcomes cosmic expansion, then the universe will eventually collapse back in on itself.

Raw material

The background fabric of the multiverse would lie beyond time and space, perhaps in the form of many-dimensional ‘branes’, or as an all-pervading ‘quantum foam’.

www.spaceanswers.com

Do we live in a multiverse?

Perpetual expansion

In universes like our own, an expansive force called dark energy seems to have grown stronger over time, overwhelming the attraction of gravity to produce an evergrowing cosmos.

Perpetual slowdown

If the forces of expansion and contraction are precisely balanced, a universe may expand ever more slowly, but will never come to a halt.

Long-lived universe

With less matter and mass, a universe might be able to expand to a huge size and exist for trillions of years before eventually collapsing back.

Short-lived universe

www.spaceanswers.com

Evidence for a multiverse? In March 2014, astronomers using a microwave telescope at the South Pole reported crucial evidence for the early inflation of the universe that may also carry hints that we live in a multiverse. The BICEP2 experiment found telltale curling patterns in the arrangement of rays from the cosmic microwave background – the afterglow of the Big Bang. Analysis of

the BICEP2 results has since shown them to be inconclusive, but these patterns are predicted to have been produced by gravitational waves that rippled across our universe as it underwent expansion. Cosmologists have argued that inflation would almost inevitably lead to a multiverse containing a large number of ‘bubble’ universes like our own.

The South Pole telescope, Antarctica

© Moonrunner Design LTD

Some universes may be so massive that the expanding force of dark energy is never able to take hold, so they rapidly collapse back onto themselves, ending in a ‘Big Crunch’.

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Space Science

What is the shape of space?

How some simple geometry and in-depth astronomy could show us the creation and future of the universe We all grow up learning that the angles of a triangle equal 180 degrees. While that’s perfectly true of a triangle drawn on a flat surface, like a piece of paper, it’s not the case for all triangles. Picture a globe and imagine the following. Start from the North Pole and draw a line down to the equator. Then take a 90-degree turn and continue along the equator heading east. Complete the triangle by making another right-angle turn and returning to the North Pole. Having already made two turns of 90 degrees, the triangle’s three angles must add up to more than 180 degrees.

Flat universe

If the three angles of a triangle add up to exactly 180 degrees, then the universe is said to be flat. Such universes are ruled by Euclidean geometry, which is named after the ancient Greek mathematician Euclid.

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The traditional 180-degree rule is part of Euclidean geometry – it doesn’t hold true on the surface of a sphere (like the Earth), which is instead governed by a set of rules known as elliptic geometry. Astronomers describe a universe shaped like a sphere as closed. A universe that follows Euclidean geometry is described as flat. Additionally, it’s also possible to imagine a shape where the angles of a triangle add up to less than 180 degrees and in this geometry the shape looks more like a saddle sort of formation. This kind of universe is referred to as open.

So, which of these three possible shapes matches our universe? In order to find out, astronomers observe the cosmic microwave background (CMB), the relic radiation left over from the Big Bang. About 380,000 years after its birth, the universe had expanded and cooled enough for electrons to become bound to atomic nuclei for the first time. This helped disperse a hot atomic fog of particles that had been keeping light trapped. Free to roam, that energy proceeded to pour outwards. It’s been travelling across the universe ever since and is what we observe as the CMB.

Closed universe Universes where a triangle’s angles total more than 180 degrees resemble a sphere and are described as closed. In this case Elliptic geometry must be used instead of Euclidean geometry.

What is the shape of space? In the billions of years since, the universe continued expanding and this radiation has now cooled to just 2.7 degrees Kelvin above absolute zero (-270.45 degrees Celsius or -454.81 degrees Fahrenheit). It blankets the whole sky and is exceptionally smooth, but crucially not perfectly so. The CMB has hot and cold spots that differ from the rest of the background by one part in ten thousand. It’s by measuring the spacing between these tiny variations that astronomers are able to probe the curvature of the universe, because on its way to us the CMB energy followed the natural shape of space, altering what we observe. High-precision measurements of the CMB from space telescopes such as NASA’s WMAP (the Wilkinson Microwave Anisotropy Probe) and the European Space Agency’s Planck have shown the universe to be near enough flat. In this case, its angles all neatly add up to 180 degrees, just like on a sheet of paper.

That’s remarkable given the huge range of possibilities. If the universe were open or closed, the sum total of the angles within a triangle could be any one of an enormous range of values. But there’s only one value that yields a flat universe: 180 degrees – however improbable, this seems to be the case. This apparent fine-tuning has been intensely debated by astronomers and physicists for decades. One possible explanation comes in the form of inflation – a slight modification to the original Big Bang theory. Tied up in the Big Bang is the idea of the ongoing expansion of the universe. Inflation says that the infant universe underwent a period of much faster expansion, growing from smaller than an atom to the size of a grapefruit in just a trillionth of a trillionth of a trillionth of a second. If correct, that would explain our universe’s apparent flatness. It could have started out open or closed, but that curvature would have been smoothed out by inflation.

“Astronomers observe the cosmic microwave background, the relic radiation left over from the Big Bang”

The Balloon-born Large Aperture Submillimetre Telescope (BLAST) looks at the CMB to see how space formed

Fate of the universe

What will eventually happen to the universe? The answer depends, in part, on its shape In a closed universe, gravity eventually overcomes the expansion and the universe collapses back in on itself in a scenario called the Big Crunch. In an open universe, there isn’t enough gravity to overcome the expansion and the universe continues expanding forever. This is known as the Big Rip. If a universe is flat, which ours appears to be, then the expansion continues but is gradually slowed by gravity. The picture became more complicated in 1998, however, with the discovery of dark energy. Having already observed that our universe is flat, astronomers expected to find its expansion slowing down. Instead, it was speeding up. Some form of anti-gravity must be pushing the universe apart at an ever-increasing rate. This means our flat universe may actually still end up in the Big Rip.

Open universe If the three angles of a triangle equal less than 180 degrees, then hyperbolic geometry rules. Universes resulting from these angles are shaped like a saddle and are referred to as open.

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How to build a

GALAXY The making of these billion-star structures has been puzzling astronomers for decades. All About Space puts together the pieces for building a galaxy

The universe is packed with galaxies. Everywhere we look and at almost every point in history we see galaxies crammed into the cosmos, grouped in clusters and great sheets that criss-cross through space-time. The most distant galaxies ever seen have been identified by the Hubble Space Telescope as being 13.2 billion light years away. Yet these are not even the most distant galactic structures out there. It’s the first galaxies that hold the record for being the furthest away from us. However, we’re yet to see them. To do so we will need the infrared prowess of the James Webb Space Telescope (JWST), which will be able to see galaxies as they are forming just 300 or 400 million years after the Big Bang – the event that threw the cosmos into existence. Understanding how galaxies form is a bit like trying to put a jigsaw together. Think of each galaxy

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How to build a galaxy

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Space Science as being a piece of that puzzle. Because galaxies are so old and evolve so slowly, when we see a galaxy in the night sky we are just seeing a single snapshot of their long lives. However, the galaxies are all at different stages of their evolution, so if we can put all these snapshots together, like the pieces of a puzzle, we can build an overall picture of how galaxies like our own Milky Way grew into the star, dust, gas and dark matter packed structures we see today. We’ve actually only known that there are galaxies in the universe beyond our own Milky Way for less than a hundred years. Before that time astronomers thought that the weird objects they dubbed ‘spiral nebulae’ were actually part of our galaxy. Their telescopes were not powerful enough to resolve individual stars in these objects, although when astronomers looked at the light coming from them, they had all of the evidence they needed to confirm that these blobs in the night sky were made up of many stars. In 1912, American astronomer Vesto Slipher found that the very light being thrown out by the spirals was Doppler shifted toward redder wavelengths, meaning the spiral nebulae are moving away from us and take on a red tint. Doppler shift is the compression or stretching of light waves as an object moves toward or away from us. You might not have realised it, but you have experienced a Doppler shift before since it also happens with sound waves. When a police car or ambulance has raced past you with its siren blaring, the pitch of the sound it makes changes depending on its distance. At first it is higher and then becomes

The filaments that make up the largescale structure of the universe can be broken down into clusters and superclusters of the various galaxies

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“He built his diagram so that its handle is made up of elliptical galaxies… which formed the prongs of his tuning fork” lower as it moves away since the sound waves become compressed and then stretched. In 1925, Edwin Hubble announced he had discovered that the spiral nebulae were all galaxies, or island universes far beyond our own. He achieved this thanks to the biggest telescope in the world at the time, the 2.5-metre (8.2-foot) mirrored Hooker Telescope at Mount Wilson in California. Hubble was able to resolve individual stars, including a specific type called a Cepheid Variable. This type of star throws out light, which varies according to its true brightness and from this observation astronomers can work out their distance. It was the Cepheids found in our neighbouring galaxy of Andromeda that allowed astronomers to measure the distance to our closest spiral as 2.5 million light years away. Coupled with Vesto Slipher’s discovery that the galaxies are all moving away from us, scientists quickly realised that once upon a time they must have been much closer together than previously anticipated. Hubble’s next step was to classify all of the galaxies in an effort to understand them as much as he could. It was from

this that he created his famous tuning fork diagram. He built his diagram so that its handle is made up of elliptical galaxies, which are galactic structures with ovoid shapes. Hubble referred to these as earlytype galaxies because he believed that all galaxies began their lives as ellipticals before evolving into one of two types of spiral galaxy, which formed the prongs of his tuning fork. One type are the regular grand design galaxies with their graceful spiral arms curving away from a small central bulge, while the second type are the barred spirals, whose spiral arms are connected with a long, straight bar running through their glowing centres. In fact, today it’s believed that our very own galaxy has a bar running through its centre. Hubble thought that the elliptical galaxies were the bulges of spiral galaxies but without the arms, which he assumed grew later. Astronomers changed their minds about this after studying galaxies in more detail throughout the 20th century. They found that elliptical galaxies form when two or more spiral galaxies collide and merge. It is the spiral galaxies that are really the early ones. So how do the spirals form? The main ingredients are gas

How to build a galaxy The stars in galaxies are made from the collapse of clouds of gas and dust under their own gravity

(predominantly hydrogen) and that mysterious substance called dark matter. Nobody knows what dark matter is, but we know it comes in the shape of giant blobs scattered throughout the universe. Some of these dark matter blobs are large enough to hold clusters of thousands of galaxies. The dark matter came first, forming these blobs, or haloes, very soon after the Big Bang. The gravity of these haloes began to attract hydrogen gas toward them, which began to flow like rivers along gravitational inclines created by the influence of dark matter into the cores of the blobs. There the hydrogen formed enormous spinning clouds and the hydrogen and dark matter formed the embryo of a galaxy. Think of the white and the yolk of an egg as the dark matter with the hydrogen at the core. Because the dark matter and hydrogen mixture was spinning so fast, it flattened into a pancake shape, taking on the characteristics of a spiral galaxy’s flat disc. Meanwhile, small pockets of hydrogen gas in the cloud collapsed to form the very first stars. These stars were gigantic, hundreds of times more massive than our relatively puny Sun and they exploded very quickly as powerful supernovae. Stars are able to create elements in their cores, while the violence of exploding stars, known as supernovae, can form even more new elements. When the first stars detonated, they spilled their guts into the baby galaxy around them, enriching it with these heavy elements. Over time, enough of these elements would build up to form asteroids, moons and planets. When we look at galaxies today, including our own Milky Way, we see vast lanes of

It's thought that galaxies are made from the collapse of protogalactic clouds of dense hydrogen and helium gas in the early universe

“The black hole in the centre of the Milky Way galaxy is four million-times more massive than the Sun” 155

Space Science

Galactic evolution How their different sizes can affect how galaxies form

Small galaxies

The making of stars

Under gravity the cloud will collapse because there’s not enough pressure from the gas itself to fight against this force pressing it down. Baby stars are made in the fight between gravity and pressure.

A lonely cloud of gas

In order for, what astronomers call a 'small galaxy' to be made, a relatively large and isolated gas cloud is needed.

Large galaxies A team of gas clouds

Small clouds of gas collapse early on to form the galaxy’s very first stars.

Gaseous add-ons A party of stars

These gas clouds with their newly formed stars clump together to make a larger cloud with a party of stellar populations.

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There isn’t much spinning going on during the making of a large galaxy. Instead, the merging of nearby gas clouds stop any chances of a disc-like structure from forming.

How to build a galaxy Forming a disc

The matter spins quickly, causing a flattened disc-like structure. At the centre is a bulge, where the older firstgeneration stars can be found. The rest of the disc is teeming with younger stars.

A galaxy with arms

Internal processes make the arms and bars found in spiral galaxies. However, if conditions are more favourable, a lenticular galaxy – an intermediate between an elliptical and a spiral – is made instead.

A gigantic galaxy

Since most of the gas needed to make a new generation of baby stars was mopped up, no more can be made. What’s left is a gigantic elliptical galaxy that’s dominated by old stars.

black dust. This dust is comprised of elements made inside the nuclear furnaces of stars, dating back to the first stars that existed about 13.5 billion years ago. Today we find that the oldest parts of spiral galaxies are their bulges. In these central regions most of the gas has been used up and the stars that exist there are crammed together and more red than the combined light of the stars in the spiral arms, which are dominated by hot, young stars. The exception is in the few tens of light years immediately around the supermassive black hole that lies in the middle of every large galaxy, where the gas is dense enough to keep forming new star clusters made of massive stars. The black holes in the centres of galaxies are enormous. The black hole in the centre of the Milky Way galaxy is four million-times more massive than the Sun. In other galaxies, black holes can be tens or even hundreds of millions of times more massive. The biggest galaxies of all, the giant ellipticals found in the centres of galaxy clusters, have central black holes with masses up to a billion-times that of the Sun, as is the case with the galaxy M87 in the heart of the Virgo galaxy cluster. Everyone knows that black holes like to consume matter, that’s how they grow so big. But black holes can’t eat everything that is served their way and sometimes they spit out their food. What happens is that as gas flows toward a black hole, it whirls around into a disc of material spiralling into the it. However, the gas brings magnetic fields with it that become wrapped up around the black hole by the swirling gas. Eventually the magnetic fields become so strong that they can actually begin to funnel away charged particles, atoms, protons, electrons and ions into jets that are so energised they race away from the black hole at almost the speed of light. We can even see one of the jets coming from the black hole in M87. The level of black hole activity can depend on many factors, such as the mass of the black hole and the amount of gas falling into it. Our Milky Way’s supermassive black hole, for instance, is very quiet with hardly any gas falling into it. Other spiral galaxies have more activity in their centres, with some emitting strong radio waves. However, the most active black holes are called quasars. The closest to us is 2.4 billion light years away, but the majority existed in the universe over 10 billion years ago. Quasars are fed by gas in two different ways: one is simply clouds of intergalactic gas falling onto a black hole in the centre of a galaxy. These clouds are clumps of gas and dark matter left over from the process of building galaxies over 13 billion years ago. The other way that quasars light up is more exciting, when two galaxies come hurtling toward each other and collide, it causes huge clouds of interstellar gas and stars to fall into the black hole. Sometimes the collision is a hit and run. The gravitational forces of each galaxy tear stars and gas out into long streamers that astronomers call tidal streams. These streams can sometimes be many hundreds of thousands of light years long. When galaxies collide it changes the future of the structures involved. Going back in time by 13 billion years, Hubble is able to see the first galaxies growing by consuming smaller galaxies. This galactic cannibalism continues even today, although at a

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Lighthouse of the cosmos

Quasars blaze radiation that can be seen from the other side of space

The ‘calm’ black hole

If a black hole is calmly sitting at the centre of its galaxy, it generally distorts the fabric of the universe around it. It leaves a dent in this sheet of spacetime from which nothing – not even light – can escape.

A swirling disc of dust and gas

An accretion disc made of gas and dust circles the black hole. If the black hole isn’t particularly active, then the matter won’t fall into it.

Heating up

When the material falls into the black hole and reaches the event horizon – the point of no return – a lot of friction is created, superheating atoms and tearing them apart.

Galactic arithmetic

The basic space formula for creating galaxies

=

+ Spiral galaxy

Enhanced spiral galaxy

Dwarf galaxy

Spiral galaxy

+

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Elliptical Galaxy

Spiral galaxy

=

much slower rate. Even the Milky Way is eating smaller galaxies at this very moment but they are not going near our black hole, so the centre of our galaxy is not active. For example, the Canis Major dwarf galaxy is only 25,000 light years from Earth and is merging with our galaxy. It contains few stars because the gravity of the Milky Way has stripped most of them away. Astronomers call such collisions minor mergers and the end result is that the smaller galaxy is swallowed up, increasing the mass of the larger galaxy. At the other end of the scale are the major mergers, between two large galaxies of around the same size. When two spiral galaxies collide like this, it destroys their spiral structures and they merge into a giant elliptical galaxy – the opposite of what Hubble’s tuning fork suggests. Amazingly, during a galaxy collision no stars actually collide, because the space between the stars is so large that the chances of two stars coming within each other’s gravitational sphere of influence is very small. That means that when our Milky Way galaxy undergoes the next phase of its growth and merges with the Andromeda galaxy in 4 or 5 billion years, our Sun will not collide with another star from Andromeda. What will collide will be the huge clouds of interstellar gas that inhabit the spiral arms of both galaxies, igniting in a huge

How to build a galaxy An active galaxy

Combine the intense magnetic field of the supermassive black hole with the ripping of atoms and super high temperatures and you get a extremely active galaxy. Electrons torn from the atoms find themselves gathered by the magnetic field.

When a black hole begins spinning into motion, it drags the fabric of space-time, or the universe, with it. This sheet gets twisted up inside the black hole.

burst of star formation. We call this a starburst and they can use up all the gas in a galaxy. This is why most elliptical galaxies, which form from mergers, have no star forming gas left and haven’t made any new stars in a very long time. All their short-lived, young stars exploded long ago, leaving ellipticals dusty and red with older, cool stars. No galaxies are being made today. All that galactic construction happened over 13 billion years ago and ever since it has been a case of galactic evolution rather than galactic formation. There are still some crucial pieces of the jigsaw missing, such as whether supermassive black holes formed before the galaxies that exist around them or vice versa, why the disc turns into spiral arms and why these arms do not wind up as they rotate around the centre of the galaxy. Some scientists think that the spiral arms are not actually rigid appendages, but density waves where stars and gas are bunching up. This is a bit like a traffic jam on a motorway and as soon as some stars hit the brakes and slow down all the other stars and gas clouds bunch up behind them. Although some of the pieces are missing, the jigsaw of how galaxies are made, grow and evolve is becoming clearer. We might not be able to see everything, but we can see enough to understand when and where galaxies came from.

Galactic jets

Funnels made by the black hole twisting the space-time fabric suck up particles, which are accelerated by electric currents, before being blasted out into space as focused beams of charged particles and radiation.

“When two spiral galaxies collide, it destroys their spiral structures and they merge into a giant elliptical”

Galaxies can merge to form unusual shapes just like Arp 142, which looks like a penguin guarding an egg

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© Alamy; ESA; NASA; Sayo Studio; Tobias Roestch

The active black hole

Space Science

How does our galaxy measure up? All About Space compares the Milky Way to other famous celestial sights

If you’ve ever been fortunate enough to see the full glory of the Milky Way in the night sky, you will know that it appears as a vast band of stars and dust, as we look towards our galaxy’s central supermassive black hole. Don’t be fooled, though; what we can see is just an estimated 0.000003 per cent of the stars in the Milky Way. Our galaxy is far too big to feasibly comprehend, measuring about 100,000 light years across with a total of about 200 to 400 billion stars, many of which host their own planetary systems. But in the grand scheme of things, our Milky Way is pretty average. It’s roughly at the halfway point for galaxies in terms of size, while about two thirds of the hundred billion or so galaxies in the universe also have the same structure – a spiral. First, let’s take a look to the lower end of the scale. The smallest galaxies we know of in the universe are so-called ultra-compact dwarf galaxies (UCDs). These extremely small clumps, stripped of their star-forming gas, contain ‘only’ about 100 million stars and are in the region of 200 light years across. The smallest and least massive galaxy that we know of – that also contains a central black hole – is M60-

UCD1, 54 million light years from Earth. It measures about 160 light years across and contains about 140 million times the mass of the Sun. Next up in the scale are dwarf galaxies, which typically contain about 100 times less stars than our Milky Way. They are typically found orbiting larger galaxies as satellites, such as the Small and Large Magellanic Clouds, which both orbit the Milky Way. But despite their size, they are thought to be the most plentiful type of galaxy in the universe – the Milky Way has about a dozen known to be orbiting it, but there may be up to 500 more that haven’t been found yet. When it comes to galaxies proper, there are three main types. As mentioned earlier, two thirds of known galaxies are spiral galaxies. These have long arms that extend for tens of thousands or even hundreds of thousands of light years around a central supermassive black hole. Some of these are known as barred spirals, like our own Milky Way, with an elongated core, thought to be caused by density waves radiating from the galaxy's centre. The biggest galaxies that we know of in the universe are elliptical galaxies, which are generally

spherical or slightly elliptical in shape and have stars that orbit randomly about their centre. They essentially look like giant blobs and typically contain older, lower-mass stars than spiral galaxies. They have the greatest range in sizes of any galaxy, from ‘just’ a few hundred light years across to a few hundred thousand. The supergiant elliptical IC 1101 is currently said to be the biggest galaxy of any type in the universe, although its size is cause for some contention as scientists have not agreed on the true boundaries of a galaxy. If the faint halo around the galaxy is taken into account, then IC 1101 is said to be 4 million light years across. The final type of galaxy is known as ‘irregular’. These do not have any distinct shape and often look stretched or chaotic in appearance. A quarter of all galaxies in the universe are irregular, but they are generally on the small side, ranging from 1,000 light years across to tens of thousands of light years. So, our Milky Way might not be particularly unique, but it is one of many fascinating groups of stars that we call galaxies that we have been able to study in the universe.

WISE J224607.57-052635.0 Distance: 12.5 billion ly Diameter: <100,000 ly Discovered earlier this year, this might be the brightest galaxy in the universe, blazing with the brightness of 300 trillion Suns. It is slightly smaller than the Milky Way.

Small Magellanic Cloud

Distance: 200,000 ly Diameter: 7,000 ly This irregular dwarf galaxy is one of our nearest neighbours, and is also the most distant object that can be seen with the naked eye in the night sky.

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How does our galaxy measure up? The Milky Way Distance from Earth to its centre: 26,000 ly Diameter: 100,000 ly The galaxy we call home. The Milky Way is fairly average in terms of size and type, with two thirds of other galaxies also being so-called spirals.

Large Magellanic Cloud Distance: 163,000 ly Diameter: 14,000 ly This dwarf galaxy is part of our Local Group of neighbouring galaxies, and is a satellite of the Milky Way. It may have once been disrupted by our galaxy.

Centaurus A

10,000 ly

Distance: 11 million ly Diameter: 60,000 ly NGC 5128 is known as a starburst galaxy, owing to its high rates of stellar formation and, like Hercules A, it appears to have relativistic jets shooting out of its central black hole.

The Sombrero Galaxy

Distance: 28 million ly Diameter: 50,000 ly Also known as M104, this galaxy is instantly recognisable for its sombrerolike shape – hence the name – which surrounds a large bulge at its centre.

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Space Science Hoag’s Object

Distance: 600 million ly Diameter: 120,000 ly This bizarre galaxy looks more like a planet; its central yellow nucleus is surrounded by hot blue stars, for reasons that are poorly understood.

The Cartwheel Galaxy Distance: 500 million ly Diameter: 150,000 ly This ring galaxy, slightly larger than the Milky Way, was thought to once have been a regular spiral galaxy before colliding with a companion 200 million years ago.

The Milky Way

Andromeda

Distance: 2.5 million ly Diameter: 220,000 ly Perhaps the most famous galaxy other than our own, the spiral galaxy Andromeda is heading for a collision with the Milky Way in 4 billion years, when it will likely consume our galaxy.

Cygnus A

Distance: 730 million ly Diameter: 500,000 ly This is one of the strongest sources of radio waves in the sky, and is perhaps best known for its role in Carl Sagan's 1985 sci-fi novel Contact.

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How does our galaxy measure up? Fornax A Distance: 63 million ly Diameter: 200,000 ly Also known as NGC 1316, this galaxy is thought to be in a process of evolution that may one day give it a huge central bulge.

Current estimates suggest the Milky Way has a mass of up to a trillion times the Sun’s

The Tadpole Galaxy

Distance: 420 million ly Diameter: 390,000 ly Officially known as UGC 10214, this barred spiral galaxy is fascinating for the 280,000 lightyear-long tail that trails behind it, possibly caused by another galaxy.

The Milky Weigh

We’ve talked about its size, but how much does the Milky Way weigh? That’s something scientists have been trying to work out with new methods. At the moment, it is thought to have up to a trillion times the mass of the Sun. However, recent research by Columbia University observed the ‘stream-like structure’ of stars in a globular cluster called Palomar 5 at our galaxy’s edge. Measuring this stream, the scientists could notice ‘wiggles’ caused by our Milky Way‘s mass. This showed that the bulk of the galaxy is 210 billion solar masses – but it does not take into account its outer regions, which may bring it much closer to the initial figure.

50,000 ly

Hercules A

@ ESO; MPIA; NASA

Distance: 2.1 billion ly Diameter: 1.5 million ly The size given here of the supergiant elliptical galaxy 3C 348 is the result of two huge jets of plasma firing out of its supermassive black hole.

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Future Tech

See how we're planning to explore and expand into space 166 20 incredible NASA projects

Wacky ideas paving the way for future exploration

176 Space colonies

The tech that could make colonisation possible

182 Asteroid nets

How NASA plan to capture an asteroid

184 10 out of this world rovers

The intrepid vehicles exploring the surface of far-flung planets

“Why would we consider leaving the only home world we’ve ever known?”

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Space colonies

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Incredible projects

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Asteroid nets

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Out of this world rovers

©NASA, Getty, Adrian Mannw

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20

INCREDIBLE

NASA PROJECTS These ideas may sound wacky, but NASA believes they could pave the way to the future of space exploration

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20 incredible NASA projects

1

Triton Hopper Name: Exploring Neptune’s Captured Kuiper Belt Object Type: Exploration Target: Triton

Thanks chiefly to its retrograde orbit – Neptune’s largest moon orbits in the opposite direction to the planet’s spin – many astronomers believe that Triton actually originated in the vast Kuiper belt of objects far beyond the orbit of Neptune, making it of particular interest to scientists. Thanks to Triton’s low gravity (equivalent to just eight per cent of

Earth’s) and its variety of terrains, NASA’s COMPASS (Collaborative Modeling for Parametric Assessment of Space Systems) engineering team has proposed a project to explore the moon with a rocket-powered ‘hopper’ capable of cost-effectively surveying multiple locations, as well as sampling the planet’s tenuous nitrogen atmosphere en route.

To ensure a ‘robust’ (ie suitably long) period of exploration, however, the COMPASS team accepts that such a vehicle wouldn’t be able to rely on battery power or – at such a distance – sunlight; it will need to refuel using only resources that are available to it on or around Triton. Hence the team’s proposal of using a radioisotope thermal rocket engine to power

the craft, which must be capable of refuelling using raw materials collected from Triton’s frozen surface and thin atmosphere. Phase I support from NIAC will enable the COMPASS team to further develop the concept and also demonstrate the validity of radioisotope thermal propulsion and in-situ refuelling.

2 Sky platform A proposed pair of glider drones high up in the atmosphere, attached by cable and positioned at different altitudes up to 914 metres (3,000 feet) apart. Upper SAIL provides lift and aerodynamic thrust; lower BOARD provides upwind force – establishing long-term platforms for Earth observation/communication.

Rocket power

Bouncing ball

Power for the probe’s systems will come from an isotope heat source: this will also be used to trigger the rocket, fuelled from local resources.

Triton having just 8% of Earth’s gravity will enable the probe to traverse the moon by ‘bouncing’ from one location to the next – with rate of descent controlled by the rocket.

Triton

With exploration missions becoming increasingly expensive, vehicles capable of acquiring data from multiple locations, and over long periods of time, are increasingly attractive.

Atmospheric sampling

Ice collected on or below the surface, or from the atmosphere using cryogenic pumping, could provide further fuel for the isotopepowered rocket.

The road to our space future

1998

NASA Institute for Advanced Concepts (NIAC) is created, operated by the Universities Space Research Association.

2005

Lunar Space Elevator: Jerome Pearson completes study on technical feasibility.

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4 Ultra-light space optics

3 Air scrubber

Constructing large space optics shaped accurately down to the scale of 1,000th the width of a human hair is an enormous challenge. ‘Photonic Muscle’ technology would enable every molecule of a polymer to control the shape of a super-thin inexpensive large curved mirror.

Space stations, like submarines, currently clean air by forcing it through a complex series of ducts and beds; recent developments in additive manufacturing and capillary fluid mechanics makes it possible to directly remove excess CO2 and contaminants using ‘thirsty walls’, significantly reducing moving parts.

5

Squid rover

Controlled explosions of electrolysed hydrogen and oxygen are used to alter the rover’s body shape in order to enable the probe to move through the water.

Name: Soft-Robotic Rover with Electrodynamic Power Scavenging Type: Exploration Target: Europa

Significant challenges face anyone wishing to remotely explore the lakes and oceans that are thought to exist under the frozen surfaces of some of the moons orbiting Jupiter and Saturn – not least ensuring that there’s enough power available to keep any probe’s systems running for a sufficiently long-duration mission. Utilising solar power is, at best, limited when you travel out as far as the gas giants, and a complete non-starter once you delve beneath the likes of Europa’s surface. As for nuclear power, there are perfectly understandable fears back on Earth concerning the very real risks of launching anything into space that includes a lot of radioactive material. “There are probably ways to make existing technology solve the problems of exploring Europa, but

2007

NASA Innovative Advanced Concepts closes after funding is removed.

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Little Big Bangs

existing technology can be expensive and may not perform very well,” says Dr Mason Peck, associate professor at Cornell University. He has successfully proposed a radical alternative; a ‘soft robotic’ rover resembling a squid, with tentacle-like structures that will harvest electrical energy from locally changing magnetic fields. Not only that, but this rover will also employ bio-inspired propulsion to move around. “The motion of this rover is inspired by nature, by creatures like squids, eels and jellyfish — all of which benefit from a highly efficient motion through the water,” he says. “In a nutshell, the idea is that the rover will ingest water from the ocean; and we use electrical power to split that water into its oxygen and hydrogen constituent molecules. When the rover needs to move, a

2009

spark ignites that explosive gas; the gas swells up part of the body of this ‘squid’, and thereby changes its shape – and when a shape changes, a body moves in the water. That’s the kind of swimming motion we’re seeking.” There’s one immediate advantage. “On Europa, we’d be able to use energy from the magnetic field of Jupiter, and water from the environment. Therefore we wouldn’t actually have to take that much hardware or combustible materials with us to Jupiter.”

US National Research Council review recommends continued need for a NIAC-like programme.

2011

NIAC is relaunched after its original closure.

Magnetic pers

Filaments enable robotic rover to ‘ sufficient electric from the constan magnetic fields e while Europa orb the gas giant Jup

20 incredible NASA projects INTERVIEW

Dr Mason Peck

Associate professor, Mechanical and Aerospace Engineering Cornell University As the former NASA chief technologist from 2001 to 2013, Dr Peck was the agency's primary advisor for its technology strategy and investments. Among his specialities is an expert knowledge of next-generation mission design.

6 Supercool shielding Cryogenic Selective Surfaces aims to model materials that reflect solar radiation, reducing temperatures without a need for active cooling – enabling long-term cryogenic storage with great potential for applications such as galactic cosmic radiation shielding and large-scale energy storage.

sonality

e the soft‘harvest’ cal power ntly changing experienced bits around piter.

Splitting water

Automatic electrolysis splits Europa’s water into its constituent hydrogen and oxygen gases, which are stored for later use in the rover’s propulsion.

Glowing skin

One option the team are considering is having the skin of the rover made out of a stretchable, electroluminescent display for illuminating the local marine environment, to facilitate underwater imaging.

Why do you think that NASA is interested in soft-robotics? To explore Europa, they’re looking for a means of creating very low-power robotic motion – simply because power will be in short supply. There may be other ways of making a low-power rover work well, but the bio-inspired approach hasn’t been investigated for this application yet, and that’s one reason why NASA is interested in pursuing this, at the exploratory stage at least, because they’re open to new ideas. So what happens next? Over the next nine months, roughly, we will create computer models and then build a prototype – sounds exotic, but we’ll be using silicone rubber and will probably be able to use off-the-shelf electrical components to produce the explosive internal motions. If we can show that this is a feasible, viable solution that collects enough power, then NASA may be able to fund a follow-on phase where we mature the technology a lot more deeply, up to the point where it can be considered seriously for a mission.

Drinking water

Sufficient ocean water is sampled through these input ports as an in-situ source of the required hydrogen and oxygen. Mission and technology specialist, Dr Peck

2012

Fusion Driven Rocket: the examination of far more efficient use of nuclear fusion in space propulsion receives Phase II funding.

2012

Two probes were sent into Earth's Van Allen radiation belts to monitor this region of space.

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7Making fuel in space

Name: In-Space Manufacture of Storable Propellants Type: Resources Target: Solar System Deep Solar System missions, especially those designed to return material and/or crews back to near-Earth space, are currently severely restricted by their need to carry all their fuel and heat shielding with them – the big problem being that it ironically takes a lot of fuel to get the required propellant off the ground in the first place. Surely it makes more sense to source fuel that’s already in space? “Delivering propellants to high-Earth orbit from the ground now costs $20 to $30 million [about £13 to £19 million] per ton,” says Daniel Faber, CEO of California-based Deep Space Industries (DSI). “Asteroid-derived fuel, delivered to high-Earth orbit, may cost as little as one tenth of current prices, making long-term space missions more practical and affordable.” The project, led by DSI chief scientist John Lewis, has been awarded a NIAC grant to fund research into fuels that can be made from asteroid material, and carried on long expeditions without requiring refrigeration or shielding – so that it only explodes when wanted! Carbonaceous chondrite asteroids are known to contain 10 to 30 per cent water and other volatiles – elements and compounds such as nitrogen, water and carbon dioxide, which have low boiling points and so evaporate from a body’s crust and/or atmosphere easily. Dormant comets may contain up to 75 per cent volatiles. The NIAC grant will allow the team to look into creating room-temperature fuels, like methane (by combining the hydrogen from water with the carbon available on many asteroids), that will not boil off during deep-space missions that may take months or years to complete.

2012

SpiderFab proposal for in-orbit construction of physically large components receives Phase I funding (Phase II funding awarded 2013).

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Harvester

Purpose: Harvesting asteroids Harvesters will initially separate out metallic elements and regolith (soil) from the asteroids and return this material for fuller processing in highEarth orbit – primarily extracting minerals and water. One reason for doing this, rather than bringing back whole asteroids, is planetary safety; it will ensure that in the event of any ‘directional errors’, any lost regolith will simply burn up naturally in Earth’s atmosphere, just like meteors.

8 Cleaning up Space The Space Debris Elimination (SpaDE) system would remove potentially dangerous debris currently in lowEarth orbit by firing focused pulses of atmospheric gases into the path of targeted debris, which would then decelerate and burn up in the atmosphere.

2014

WRANGLER: Capture and De-Spin of Asteroids and Space Debris is one of 12 proposals awarded funding.

2015

Soft-Robotic Rover with Electrodynamic Power Scavenging (squid rover) is funded.

20 incredible NASA projects

Firefly

9 WindBots

Purpose: Asteroid prospecting These tiny Firefly-class craft (each about 30cm/11.8in long and 15cm/5.9in wide) are intended to investigate near-Earth asteroids (NEAs), using spectral imaging and other non-intrusive methods. This will enable Earth-based scientists to confirm the size, shape, spin and composition of NEAs and in turn help determine the most appropriate targets for DSI’s first harvesting missions.

10

These autonomous robot explorers, being developed under Adrian Stoica at NASA’s Jet Propulsion Laboratory (JPL), would operate within the atmospheres of Jupiter or Saturn – remaining in-situ by harvesting energy locally from the planets’ strong winds and magnetic fields.

CubeSat planetary explorer

Name: CubeSat with Nanostructured Sensing Instrumentation for Planetary Exploration Type: Exploration Target: Solar System

DSI-wheel-slider

The last 15 years have seen the development of CubeSats – lowcost, ten-centimetre (3.9-inch) cubed miniature satellites built from commercial off-the-shelf components. This NIAC proposal by Dr Joseph Wang, associate professor of astronautics at the University of Southern California, will investigate the potential of CubeSats to provide low-cost, in-situ analysis of the surface composition of asteroids and comets.

Key to this project are cheap, lightweight, compact, disposable sensors that can accurately detect 74 trace elements in the range of parts per billion. The instrument is low cost, low power, low mass, compact, and disposable – making it a perfect match with the CubeSat ethos. The NIAC funding enables the project to focus on the feasibility of a CubeSat-based mission to small asteroids or comets. These mini satellites are cheap and easily manufactured

Purpose: Asteroid processing

After the Harvesters have unloaded their cargo, orbital processing systems will begin the detailed operation of separating out the most useful elements: initially, these are likely to be water, organic compounds of hydrogen and carbon, and oxygen – all of which can be utilised for propulsion and/or life support in space – without the costly need to bring them up from Earth.

2015

V2Suit for space habitation and exploration is tested by NASA in microgravity environment.

2016

OSIRIS-REx launch an unmanned mission to study and return samples from asteroid 101955 Bennu by 2023.

2017

ESA and JAXA will launch the BepiColumbo satellites to perform a study of Mercury.

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12 Brave new 3D world

3D printing is all the rage on Earth, but could be invaluable off-world, enabling space travellers and settlers to print anything from task-specific tools and composite building materials to food and human tissues – with a system utilising any in-situ resources.

11

Seeing inside asteroids

Surface

Most asteroids are irregularly shaped although a few, like Ceres, are nearly spherical. They are invariably pitted or cratered, with a thin covering of dust.

Name: Seismic Exploration of Small Bodies Type: Resources Target: Asteroids Jeffrey Plescia of Johns Hopkins University, has a different proposal for using CubeSats to examine the interior structure of asteroids and comets. The proposed project will combine micro-seismometers with CubeSats to create impactors capable of investigating the interiors of asteroids and comets. The scheme involves the placing of one or more micro-seismometers onto the surface of the target small body and then utilising the oldest scientific technique in the book – hitting the asteroid or comet with something! However, because the impact will produce a known signal, the resulting seismic data can then be interpreted using the same techniques as seismic surveys on Earth, providing data on

Core

An iron-nickel core is evidence of a previously molten state, in which rock and metal separated; the denser metal sinking to the centre.

2018

Inside a giant space rock

Mantle

The mantle is likely to consist of silicate minerals such as olivine, which contains magnesium, iron, oxygen and silicon, with trace amounts of other elements.

ExoMars rover (joint ESA/Roscosmos mission searching for signs of Martian life) launches.

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the seismic velocity – and the interior structures – of the target space body. According to Plescia, this kind of seismic survey technique could show whether asteroids are just piles of rubble or have solid interiors with fragmented surface layers, and whether comets are homogenous throughout or contain a rocky core. “This implementation represents a novel approach to understanding a key science question for small bodies – their interior structure – using a new kind of instrumentation in the context of a single or multiple small-scale spacecraft,” says Plescia. “This would present a low-risk, highreturn opportunity to understand a key question related to science, exploration and Earth-hazards.”

2018

Crust

Protoplanet Vesta appears to have a crust of solidified basaltic lava, thought to have frozen after oozing out of the asteroid’s interior when it formed about 4.5 billion years ago.

Launch of the James Webb Space Telescope, the successor to Hubble.

20 incredible NASA projects

13

Interstellar mini explorers

Name: DEEP IN Directed Energy Propulsion for Interstellar Exploration Type: Exploration Target: Deep Space It has taken the best part of 40 years for Voyager 1 to reach the edge of our Solar System. Professor Philip Lubin of the University of California has gained NIAC support to further investigate a potential system that will up humanity’s game when it comes to the next generation of interplanetary and interstellar exploration. Lubin’s approach is to look at pairing directed energy propulsion with wafer-

thin spacecraft, creating tiny probes propelled by phased arrays of lasers. These wafer satellites could be boosted to extremely high speeds and become humanity’s first interstellar probes. “One of NASA’s goals is to explore other planetary systems by remote sensing, sending probes and eventually life to explore,” he says. “A step in this direction is to send small probes that will supplement the

current long-range remote sensing done by orbital telescopes.” The project relies on research done on a proposed planetary defence system called DE-STAR, which would use a modular phased array of lasers to target and vaporise objects threatening the Earth. The project aims to prove that this asteroid defence technology can be adapted for interplanetary and interstellar exploration.

At the poles, crater walls and other features ensure that some parts of the Moon are in permanent shadow

15 Cricket rovers

Name: CRICKET (Cryogenic Reservoir Inventory by CostEffective Kinetically Enhanced Technology) Type: Resources Target: The Moon

Many people still think of the Moon as a dusty, dry wasteland, but Jeffrey Plescia and Larry Paxton of Johns Hopkins University plan to explore the permanently shadowed regions (PSR) on the Moon to find and extract the ice and other volatiles believed to be there. CRICKET would employ a small herd of robots, or ‘crickets’, to hop, crawl and roll while exploring the shadows; a carrier hive to collect data, provide Mother ship The direction and power and disperse the crickets; and function of the probes an orbiting ‘queen’ to deliver the robots can be supervised and and provide communication. “Each controlled centrally. element is a reasonable extrapolation of existing CubeSat and/or commercial technology,” Plescia says. “Each cricket carries a tiny SWIR and far-UV MEMS The development of lightweight, spectrograph, Xenon lamp, economical thin film lenses for new heating element ‘proboscis’ and telescopes could rapidly reduce their cost ‘whiskers’ for characterising while increasing their size beyond what is the volatiles. We use multiple currently technologically feasible, by using crickets to achieve a highaberration correction techniques previously resolution map and to mitigate developed for laser communication. risk of failure.”

Light propulsion

These probes can be pushed deep into space using photon pressure from laser light. In theory this technique could accelerate low-mass probes to relativistic speeds.

14 Film lenses Compact

Given the scale of the wafer probe units, hundreds could be released from a relatively small vehicle parked in orbit.

2020

Robotic capture and retrieval of a selected asteroid, brought into lunar orbit.

2021

NASA’s Exploration Mission 2 (EM-2): The first crewed Orion spacecraft mission will retrieve samples from a previously captured asteroid.

2024

Launch of ESA’s PLATO (Planetary Transits and Oscillations of stars) space observatory, looking for rocky extrasolar planets.

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Pulsars might soon become a key component in an interplanetary navigation system

Sunlight drilling

Name: APIS (Asteroid Provided In-Situ Supplies): 100MT of Water from a Single Falcon 9 Type: Resources Target: Asteroids APIS has been proposed by Dr Joel Sercel, former director of Caltech’s Laboratory for Spacecraft and Mission Design and founder of California-based ICS Associates Inc, as a way to solve the problem of finding useable water in space. He believes that the system could harvest and return up to 100 tons of water from a near-Earth asteroid using a single Falcon 9 v1.1 launch. APIS is based on a new process called ‘optical mining’, in which highly concentrated sunlight is used “to drill holes, excavate, disrupt, and shape an asteroid” while it’s enclosed in what’s essentially a giant bag, made of heat-containing material.

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After the asteroid has been ‘bagged’, direct solar-thermal energy is used to extract the water it contains into the enclosing bag from which it’s pumped out into a separate container and stored as solid ice. After several months of collection, Sercel believes that up to 120 megatons of water could be stored in this way, although a small proportion would be then used to propel the APIS system back to the vicinity of the Moon’s orbit where the ice can be used to support a more affordable programme of human exploration.

The end of extended agreements relating to use of the International Space Station (ISS). The ISS itself is likely to be decommissioned and de-orbited at a later point, replaced by commercial and/ or government-owned platforms.

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17 Interplanetary GPS Name: A Tall Ship and a Star to Steer Her By Type: Exploration Target: Deep Space

As Douglas Adams once pointed out, “space is big. Really big”. And potentially easy to get lost in. This poetically titled project was proposed by the Massachusetts Institute of Technology’s Michael Hecht, and essentially aims to use radio observations of various cosmic phenomena – quasars, pulsars and masers – as navigational beacons for deep-space missions. If it works, it could become the interplanetary equivalent of GPS for spacecraft The Variable Vector Countermeasure travelling between planets Suit (V2Suit) is a spacesuit specially and even beyond the Solar designed to help keep astronauts System. At this stage, healthy on long-term space NIAC will help fund a exploration missions and help preliminary catalogue of stabilise them as they live and work reference maser sources, in microgravity – using flywheels a system analysis, and to replicate the sensation of gravity conceptual design of a during movements in zero-g. demonstration mission.

18 Suits you!

2027

Mars One (unrealistically) expects to land the first human settlers on the Red Planet.

2030

Both Russian and Chinese space agencies aim to put humans on the Moon again by this date.

20 incredible NASA projects

19 Landsailing… on Venus!

INTERVIEW

This proposed landsail-propelled Venus rover aimed to take advantage of the second planet from the Sun’s dense atmosphere and relatively flat surfaces to explore what remains of one of the most hostile environments in the Solar System – in terms of temperature, air pressure and corrosive atmosphere.

NIAC programme executive NASA Senior technology analyst Jason Derleth is an aerospace engineer with NASA's Innovative Advanced Concepts (NIAC) programme. He has helped NASA refocus some of its technology towards returning to the Moon and he is also a budding author in his free time.

Deformable mirrors are already in use at the European Southern Observatory’s Very Large Telescope in northern Chile, but they could be significantly bigger and better

Deformable mirrors

Name: A Precise Extremely Large Reflective Telescope Using Re-configurable Elements (APERTURE) Type: Observation Target: Deep Space Melville Ulmer at Northwestern University is partnering with researchers at the University of Illinois (UIUC) to investigate the feasibility of creating optical telescope mirrors that can be shaped using a magnetic field. Northwestern University will work on the materials and the magnetic shaping process, while UIUC will focus on coupling the deployment design to a flying magnetic write head (which will shape the mirror) design. Much of this NIAC-funded research will explore ways of ensuring the mirror’s shape is precisely correctable and can be maintained for long periods, ensuring a minimal need for regular maintenance.

2030s

NASA’s manned Mars mission is scheduled to land on the Red Planet in this decade.

What is the purpose of NIAC? Ideally, NIAC studies have an impact on the research community and potentially the wider aerospace community. A good past example of what we hope for is the study on space elevators from the late-Nineties. After the NIAC study, they became a potential future launch system in which other organisations have invested money. Is it difficult to make the selections? Selecting the best of the best is always tough, but NIAC has two unique problems: first, we are open to any kind of technology, so we have to understand enough about what the proposal is saying to be able to compare, say, a new in-space rocket engine to a new way of detecting background radiation. Second, we try to be on the edge of science fiction without putting our toes over the line. Part of the reason why we're okay with the risk is that we expect some of our ideas to provide substantial improvements: higher performance, lower cost, lower mass, lower complexity, better science.

NIAC’s Jason Derleth toes the line between science and science fiction

Precision deformations can be made in the mirror by magnetic fields

2037

Lunnyj Poligon - a Russian robotic lunar base - is scheduled for completion by this date.

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© NASA; Adrian Mann; ESO; Tobias Roetsch; DSI PR

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Jason Derleth

SPACE COLONIES To ensure the long-term survival of the human race we will one day need to colonise the stars. Will these be the technologies that make it possible?

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Space colonies Discussing space colonies, let alone seriously considering them, can seem a bit fanciful at first, if not downright ridiculous. After all, there is still ample room for humanity on planet Earth. Most people are seeing an overall increase in the quality of life which doesn’t look like abating. Why, then, would we consider leaving the only home world we’ve ever known? Consider, for starters, that by the middle of this century most expect Earth’s population to be approaching the 10 billion mark. That ample room may not seem so ‘ample’ any more by then. Our resources are also not infinite; we will one day run out of oil, coal and certain metals. And the threat of a civilisation-ending event is ever-present, be it an unseen asteroid like the one that wiped out the dinosaurs or a disaster of our own creation. Humanity will one day, for one reason or another, need to leave planet Earth if it is to survive. So why should we not begin the development of technologies that might enable us to do so now, as we begin to find our feet in the realm of space exploration? From Moon bases to orbiting outposts to colonies on Mars, there is no shortage of proposals for ways we could begin to inhabit other regions in the Solar System. We are limited by the means in which we can access space, namely using rockets for now, but even that has not stopped us landing on the Moon and building a small space colony - the ISS - to date. On 12 July 2006 a Russian Dnepr rocket, essentially a refurbished ballistic missile, launched into orbit from a remote town near Russia’s southern border

called Yasny. Although it was the first launch of a Dnepr-1 as a space rocket, it would likely have gone mostly unnoticed had it not been for its rather unique payload: Genesis 1. Designed and built by Bigelow Aerospace in Nevada, this satellite began its life not much bigger than a person, but it would be difficult to downplay its significance. From this nondescript town in Russia, the beginnings of humanity’s serious attempt to colonise the cosmos had begun. This wasn’t just any regular satellite; it was a specially designed module launched in a compact form as a precursor to fully fledged space hotels. Upon reaching orbit it was purposefully pumped full of gas, expanding in size to that of a large car in just ten minutes. The experimental module was designed to prove that, in the future, we wouldn’t need to launch entire modules or structures like on the International Space Station. We could launch them folded up before inflating them in orbit at a reasonable cost. It served as proof that space tourism, and space colonisation, was possible. Tourism is regarded as being a key aspect for any future space initiatives. The money that might become available would not be enough to sustain future colonies on their own, but it would provide the initial cash injection needed to build the other technologies needed to live in space. “A tourist market is potentially profitable and can spur the development of launch vehicles, habitats and life support,” space settlement expert and NASA contract scientist Dr Al Globus tells All About Space. And he’s right. If we are ever to truly colonise the cosmos,

most view space tourism as a key stepping stone to making it financially viable. If, one day, we get to live among the stars, it will not have been an easy ride. Actually getting into orbit is hard enough, let alone permanently living there. However, there are many experts, agencies and organisations that are of the belief that living in space is not only a possibility, but a necessity. Whether it’s a lack of resources on Earth or the potential for a planet-wide disaster, there is a growing belief that if humanity is to survive long into the future, it will not be enough to simply exist on Earth. “Life completely covers our planet, but is alone in the Solar System and possibly in the universe,” says Dr Globus. “We inhabit a thin layer on the third rock from the Sun, and that makes civilisation, humanity and life itself vulnerable. Space settlement can end that vulnerability by expanding throughout the Solar System and, in the very long term, to the stars.” But as Dr Globus points out, the single biggest obstacle to colonising space is the cost of escaping our planet. Launching rockets is not cheap – it costs thousands of dollars just to get a kilogram of anything into space, and that’s assuming you already have a rocket ready to launch. Thankfully companies like SpaceX are rapidly bringing the cost of launching equipment to orbit down, and it has once again got people dreaming of building colonies in space. In the modern day we already have a colony of sorts in orbit; humans are constantly flying round

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Future Tech our planet in the ISS at any one time. Of course the cost, and time taken to build the ISS, was enormous. It required dozens of rocket launches, approximately £64 billion ($100 billion) and decades of construction just to finish it. It is unlikely any nation will want to attempt such a long, costly endeavour again soon. So looking to the near-future, it has been suggested that we again look to our largest natural satellite, the Moon, as a potential source for colonisation. We have, after all, been there before and in cosmic terms it’s just a stone’s throw away. NASA has hinted that, beyond the retirement of the ISS in the 2020s, it might seek to build a ‘gateway’ space station in orbit around the Moon, to be used by astronauts on their way to further destinations. Others like ESA have already thought of some ambitious designs to build a base on the ground. Using robots they say it might be possible to 3D print entire designs on the lunar surface, perhaps using material from the Moon itself to build structures. In terms of actually getting humans permanently into space, beyond low Earth orbit, colonising the Moon is by far our best bet for now. “The Moon is a potentially important source of materials with which to construct space settlements,” explains Dr Globus. “One can imagine gigantic 3D printers ‘printing’ entire space settlements, but that will take a bit of technology development!” Dr Globus also points out a key difference he sees between building a base on the Moon to be inhabited by workers, and a settlement to be inhabited by regular people. “You go to a base to work. You go to a hotel to play. You go to a settlement to live,” he states. He has a point – building a base on the Moon would almost certainly begin as a scientific outpost; when would a regular person be given the opportunity to live out the rest of their days in a space colony?

Moon colony 01

Power

Spacesuits

The Apollo spacesuits were workable, but clunky. Astronauts often fell over or lost their footing. Future spacesuits, therefore, will need to be much more versatile with joints and easier access to make sorties on the Moon more manageable. 02

Communications

It might seem trivial but communications to and from Earth, and to any orbiting outposts, will be key for future space settlements. To report problems or request supplies, a permanent communications network will be a necessity. 03

Food

Growing crops on the Moon will be difficult, but not impossible. It has already been proven that crops can be grown on the ISS. A future lunar colony will certainly need enclosed greenhouses in order to remain partially self-sufficient. 04

Nuclear fusion For a future lunar base solar power alone might not be enough. One solution is nuclear fusion, the same method of energy the Sun produces at its core. Using a powerful laser system the National Ignition Facility (NIF) in California can create the pellet of fuel seen in the attached image, which is capable of powering an entire home. Perhaps this will be the fuel of choice for future space missions.

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Solar panels

While nuclear fusion may be the breakthrough in power we need, solar panels will still have their place. After all, the Sun is a renewable source of energy that will not run out – for 4.5 billion years at least. 05

Self-replicating buildings

3D printers In Star Trek characters were often shown ordering food and other objects from replicator machines, which used energy to make almost anything you wanted. Today in the real world we have a new industry still in its infancy that is moving towards a similar goal: 3D printing. Creating tools and objects out of material has already been tried and tested. Now, some are suggesting that lunar soil, or regolith, could be fed into machines delivered into the surface to build entire structures, rather than having to transport them there from Earth.

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Recycling

On the ISS almost all of the water, including urine, is recycled to ensure the station doesn’t need constant resupplies of oxygen and water. The same level of recycling will likely be needed on the Moon. 06

Inflatable habitats

Using inflatable modules on the Moon could ensure that the launch requirements to get there are kept low, and the cost of actually getting things to the surface could also be reduced.

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Space colonies

“The Moon is a potentially important source of materials with which to construct space settlements” Dr Al Globus

Lunar travel 04 03

Morpheus If we want to travel to and from the Moon, having a spacecraft that can easily take us to the surface and back to lunar orbit is key. Step forward Morpheus, NASA’s prototype lander that it has been testing on Earth. With a precision much greater than the Apollo landers, Morpheus could take 500kg (1,100lb) of cargo to and from the Moon up to a spacecraft or station in orbit.

06

Resource utilisation

Mining In the past few years several companies on Earth have stated their ambition to mine asteroids and bring the spoils back to Earth, or use them in space. Similarly, some think the Moon may be abundant in useful substances that could be used by future colonies. One such ‘holy grail’ is helium-3, an isotope rare on Earth but abundant on the Moon that could be used in nuclear fusion. Quite how useful helium-3 is remains to be seen, but mining the Moon would be key to providing the materials needed for a future colony.

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Future Tech The colonisation of the Moon will be an imperative step towards building space colonies. Some have suggested that NASA, before attempting its ambitious (although plausible) attempt to land humans on Mars in the 2030s, should consider first building an interim base on the Moon. If the cost of getting to space can be greatly reduced, akin to paying for a flight to a distant city on Earth, and the technologies for space habitation can be proven, then there is little reason to think there might not one day be entire towns and cities in orbit. And this will not just be some modular design like the ISS. In decades gone by artists have imagined fanciful structures where people live out their lives in similar conditions to those experienced on Earth. One design many favour is a Stanford torus. This is essentially a giant rotating cylinder where humans would live on the outer rim and the centre would be hollow. The rotation would provide artificial gravity for people to live in at a similar level to living on Earth. Crucially this would mean that, living for extended periods in space, human bodies would not deteriorate in a low-gravity environment, like they do on the ISS. This would truly enable humans to travel to and from a space colony just like they do cities on Earth. In an ideal scenario the cylinder would be the size of a large building or even a skyscraper on Earth with all the amenities that would be expected from a ground-based settlement. “It’s a place to live in space,” explains Dr Globus on the benefits of such a colony. “It provides atmosphere, water, food, shelter and pseudo-gravity suitable for people to live and raise their children – not to mention have a good life.” There are many steps that must first be taken before such a colony becomes a reality. The rise in the private space industry for one is important, as it provides new means to access space. Aside from SpaceX there is the Orbital Sciences Corporation, which dramatically lost one of its rockets in October but still remains a major player in the industry. And space tourism companies, too, will play a big part. If people are willing to at first pay for brief forays into space, then ultimately the money could be available to build larger, more permanent settlements. A time frame for when this might happen is hard to nail down, but Dr Globus is optimistic about colonisation. “[In 100 years] I expect a few tens of thousands of people to be living in space – and that is just the beginning,”

Stanford torus 01 Radiation shielding

Space explorers not only have the Sun's rays to contend with, but also cosmic rays from elsewhere in the universe that can be harmful, if not fatal. Any future space colony will need sufficient shielding, likely a layer of water, to keep people protected. 02

Artificial gravity

A Stanford Torus will be a spinning space station that supplies Earth-like gravity conditions thanks to the centrifugal force. A plan to test a centrifuge on the ISS was scrapped in 2005, but there are hopes plans to test the technology again will be made soon. 03

Docking

Currently on the ISS there exists a International Docking Standard which allows any spacecraft to attach to the ISS if it has the right docking module. In a future Stanford Torus the centre, as it does not rotate, will be at zero-gravity – the ideal place for spacecraft to dock, perhaps also using a universal docking standard.

04

Composition

A future orbiting space colony will need to be made of something sturdy enough to cope with the pressures of rotation and micro-meteoroid impacts. A “miracle” material like graphene that is both light and strong might provide the specific composition required. 05

Agriculture

Like a colony on the Moon, learning how to grow crops in space will be essential for a space colony. Current research on the ISS will provide the know-how needed to make this possible. 06

Mining the Moon

Perhaps aside from mining asteroids, getting resources from the Moon might also be appealing for a future space colony. Space guns on the Moon could almost literally “fire” cargo-containing spacecraft to the space colony in Earth orbit.

Spaceplanes

Skylon Rockets will be useful for getting cargo and even people into space, but they are not exactly simple to operate. What if, instead, people could take off from the surface of Earth in aircraft-like spaceplanes and reach an orbiting space colony? That’s the dream of British company Reaction Engines, who is hard at work developing a revolutionary spaceplane called Skylon that could reach space by taking off from specialised runways on Earth. While NASA’s Space Shuttle was impressive, Skylon could be the first true spaceplane if it ever comes to fruition – and it could lead to a future where spaceplanes are commonplace.

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02

Asteroid mining

Arkyd For any future space colony, resources will be key. It’s unlikely they’ll be unable to rely solely on supplies from Earth so, instead, they will have to use the resources available in space. One such source could be asteroids, which are rich in metals and also water. Washington-based company Planetary Resources is planning to look for suitable asteroids to mine using its Arkyd telescopes, before sending spacecraft to selected targets to bring resources back to Earth, in addition to storing resources in orbit for use in space. It’s likely that future space colonists will have companies like this to thank for proving asteroid mining is possible.

Space colonies

05

Megastructure SpiderFab

04

One of the biggest challenges to building a giant space settlement like a Stanford torus will be, well, actually building it. How will we get all the material into orbit, let alone construct it into a giant floating city? One company has a solution: Washington-based Tethers Unlimited is creating a machine called SpiderFab that uses a sort of 3D printing to construct giant ‘trusses’, or meshed backbones, in space. This might be the technology used to construct space stations of the future.

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03

Launching

06

Grasshopper Getting to and from orbit is not cheap, but SpaceX thinks it can lower the costs by creating reusable rockets that can launch and land on Earth. It’s currently testing a prototype rocket called Grasshopper that has been performing small ‘hops’ above Earth’s surface to a height of a few hundred metres to prove rockets can touch down safely after lifting off. Ultimately SpaceX will soon bring entire rockets back from orbit, and lowering the cost of launching in this manner instead of using expendable rockets could make space more accessible.

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Future Tech

Asteroid nets NASA’s latest space fishing trip aims to capture an asteroid and bring it closer to Earth to study

Orion spacecraft

NASA’s new spacecraft, which will carry a crew of up to four astronauts in or beyond low Earth orbit – to the asteroids and Mars.

“This mission represents an unprecedented technological feat that will lead to new scientific discoveries”

Asteroid grabber

An alternative concept for a solar-electricpowered spacecraft, with inflatable rings to capture a small nearEarth asteroid.

Astronaut

An astronaut prepares to take samples from the captured asteroid after it has been relocated to a stable orbit in the EarthMoon system.

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Rings

Hundreds of rings are affixed to the asteroid capture bag, which help astronauts to carefully navigate the surface.

WRANGLER’s GRASP

WRANGLER (Weightless Rendezvous And Net Grapple to Limit Excess Rotation) will trap and de-spin asteroids with a big GRASP net, tether deployer and winch mechanism.

The SpinCASTER

Once the asteroid is in the WRANGLER net, its inflatable tubes are deflated and the winch closes the net, absorbing the asteroid’s momentum.

In June 2010, the Japanese Hayabusa probe succeeded in returning to Earth some dust samples from a distant, stoney asteroid known as 25143 Itokawa. Until now, such missions have rarely been successful because returning samples to Earth is very difficult. But what if the asteroid was closer? Since 2013, NASA scientists have been working on a plan to identify and capture a small near-Earth asteroid – anything up to about eight metres (26 feet) in diameter – and then redirect it into a stable orbit around the Moon, where it would be accessible to Earth-based astronauts. Current theories suggest that asteroids are part of the leftover materials from the formation of our Solar System, remaining largely unchanged since then. Having one of these pristine ‘time capsules’ on our astronomical doorstep would enable far more samples to be returned to Earth. It could potentially lead to numerous new scientific discoveries about the evolution of the Solar System and even the beginning of life on Earth itself. NASA’s Asteroid Redirect Mission (ARM), has begun to identify suitable candidates; in less than two years, NASA’s Near-Earth Object Program has already catalogued more than 1,000 new near-Earth asteroids. As of September 2014, three had been confirmed as valid ARM targets. Although the clever money is on the inelegantly named asteroid 2011 MD – which missed the Earth by about 12,200 kilometres (7,600 miles) back in 2011 – more candidates are likely to be discovered during the next few years, giving NASA experts the best choice possible. The ultimate decision will be informed by factors such as an asteroid’s location, speed, orbit, size and rate of spin. The ARM robotic spacecraft will likely be launched at the end of the decade; NASA is yet to confirm whether it will opt for a scheme using an inflatable system, similar to a bag, to capture a small asteroid complete, or use a robotic arm to snatch a boulder off a much larger asteroid instead. Critics have pointed out that the manned retrieval of samples is unnecessary, because thousands of meteorites have already been analysed. However, NASA administrator Charles Bolden has insisted: “This mission represents an unprecedented technological feat that will lead to new scientific discoveries and technological capabilities and help protect our home planet.” In addition, scientific offshoots will come from the development and demonstration of space technologies, which will be important to the exploration of Mars. Principle among these is its use of advanced Solar Electric Propulsion (SEP); which create electromagnetic fields to accelerate and expel charged atoms called ions, for very low thrust and efficient use of propellant. Thanks to its SEP system, the ARM mission will use between five and ten times less propellant compared to conventional chemical propellant sources. The mission will provide practical trajectory and navigation experience, comparable to safely landing on Mars. While the ‘asteroid mass’ chosen will be of a size and mass sufficiently small to burn up in Earth’s atmosphere without causing any harm, ARM will nevertheless demonstrate possible planetary defence techniques to deflect future dangerous asteroids.

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© Adrian Mann

Asteroid nets

10 out of this

world rovers These intrepid vehicles enable us to actively seek out and explore areas of a planetary surface in minute detail, far beyond the landing point of a spaceship

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10 out of this world rovers

The incredible Curiosity rover is a mobile geological and chemical laboratory, with the goal of discovering if Mars is (or was) the home of microbial life forms

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Lunar explorers

Roving vehicles have been sent to the Moon and Lunokhod 1 Mars since the 1970s. They need to be robust enough Country: USSR to survive the massive g-forces at launch from Earth, Launch date: 10 November 1970 the journey through space and the impact of landing. Mass: 756kg (1,667lb) They are usually delivered to their destination by a Looking like a tin bath with wheels designed by Wallace lander craft that has retrorockets to slow down the and Gromit, it isn’t the most stylish lunar rover and its descent, with parachutes and air bags also being used achievements were overshadowed by the US Apollo manned Moon for landing on Mars. In the case of the large Curiosity landings, even though it is the first remote-controlled lunar rover. rover, the sky-crane technique was used to make a The craft had eight wheels that each had an electric motor for better more precise landing. manoeuvrability. When it landed on the Sea of Rains, a crew of two The use of rovers greatly adds to the amount of engineers drove it off the landing stage of the Luna 17 spacecraft. The driver used images from the rover’s two pairs of TV cameras to plot its territory that can be explored. Orbital craft can take course, while the other crew member steered the craft’s aerial to keep lots of pictures and collect data, which make us it in line with Earth, maintaining radio communication and control. To aware of the best places that are worth investigating provide power to the batteries, Lunokhod 1 opened its convex lid in detail. A lander craft can bristle with tools and during the day to expose solar cells positioned inside. During the instruments to gather lots of information about a USA night, the lid was closed and a radioisotope heater kept its specific site, but you need a rover to seek out worthy components warm. It performed incredibly well, taking an areas to study in fine detail. China impressive 500 soil samples, sending back 20,000 A rover requires a structure that protects its vital close-up and 206 panoramic pictures of the electronic systems and wheels, with steering and lunar surface and travelling a total of USSR suspension that can cope with rough terrain and 9.93 kilometres (6.17 miles). slopes. It also needs energy sources to power the motors and systems, usually from solar panels, batteries, nuclear heaters and cameras to provide information about its location and to guide navigation. Computers are required to process Astrobotic Lunar information and to navigate the vehicle, antennas Spelunker send and receive data to robotic arms or hands Country: USA Launch date: Concept vehicle that deploy equipment and use tools to obtain rock Mass: To be confirmed samples. Sophisticated rovers like Curiosity can This is a rover concept that would be employed to explore operate independently until they receive further skylights and tunnels on the Moon or Mars. These geological commands from one of the Earth-based mission structures are too dangerous for astronauts to explore, so the control centres. alternative is to use robots that could autonomously rappel into and traverse these underground voids. This would be a big leap On 31 July 1971, Dave R. Scott was the first from current roving vehicles, which depend heavily on human person to drive a rover on the lunar surface controllers, meaning they tend to move very slowly. Using during the Apollo 15 mission. The first trip was the technological expertise of Astrobotic Technology, a a circuit around the Lunar Module and then ‘Spelunker’ concept mission has been funded by NASA a longer visit to the Elbow crater was carried that would land a spacecraft near a lunar cave or out to obtain rock samples. Apollo 17 sent skylight. A power and communications hub would the third lunar vehicle, which made a record be lowered into the void, releasing roving robots 35.74-kilometre (22.2-mile)-long journey. Since to carry out a full survey of the environment. then, there have been no other manned vehicles, This activity would add to our knowledge of the geology of these localities, making way although several concept vehicles have been for human explorers and even human considered and they will no doubt follow the tracks habitats, testing the capabilities of of the robot rovers in the near future. these robotic devices operating in these hidden lunar realms.

These lunar rovers have changed the way we see the Moon's surface

Key

02

A popular destination The Mare Imbrium is a 1,145-kilometre (711-mile)-wide diameter impact basin, formed about 3.8 billion years ago. Since then, it has been flooded with lava to form a large and relatively flat area, making it an ideal landing spot for manned and unmanned missions to explore the geology and formation of this region. Lunokhod 1 visited in 1970, 250 kilometres (155 miles) south-west of Laplace A, and in the following year Apollo 15 landed near the Apennine mountain range on the south-eastern rim of the area. China’s Jade Rabbit was intended to land at Laplace A, near the boundary between Mare Imbrium and Sinus Iridum, the Bay of Rainbows, but ended up landing to the north-east of it, just south of Laplace F, a crater in the Mare Imbrium.

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Bianchini

Sinus iridum Promontorium laplace

Laplace A Promontorium Heraclides

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10 out of this world rovers

Jade Rabbit (Yutu)

Country: China Launch date: 01 December 2013 Mass: 140kg (308lb) Yutu has a box-like body, with two large solar panels deployed on each side, providing power for its six cleated wheels. A suspension system allows it to drive over 20-centimetre (7.8-inch) obstacles and cope with 20-degree slopes. Despite being remote-controlled from Earth, it features autonomous navigation systems. Its main objective was to survey the structure of the lunar surface using spectrometers and ground-penetrating radars, to develop the technology for the long-term Chinese Lunar Exploration Program. It managed to travel 100 metres (330 feet) and spent just over a month on the Moon taking photos and examining the soil, before several system failures stopped it moving on 25 January 2014.

04 Lunar Roving Vehicle

Country: USA Launch date: 26 July 1971 (Apollo 15) Mass: 210kg (463lb) It took 17 months to design and build the ‘Moon Buggy’ at a cost of £25 million ($38 million). The four-wheel drive, electricpowered buggy was built to carry two astronauts and all their bulky lunar exploration equipment, plus life support systems. Special spacesuits that could bend at the waist were created so that the astronauts could sit in the buggy and it had a multi-function T-handle control that enabled either astronaut to steer, accelerate or stop the vehicle. The 3.1-metre (10.2-foot) chassis was constructed of aluminium alloy tubing and it could carry a load of 490 kilograms (1,080 pounds), just over twice its own mass of 210 kilograms (460 pounds). Its average speed was around nine kilometres (5.6 miles) per hour and it could travel a maximum of 7.6 kilometres (4.7 miles) from the Lunar Module. An onboard navigation computer kept track of where the buggy was in relation to the Lunar Module and a colour TV camera sent images back to Mission Control to provide additional navigation advice and directions. Moon buggies were successfully used to travel across the lunar surface by the Apollo 15, 16 and 17 Moon landing missions.

Athlete

05

Country: USA Launch Date: Prototype Mass: 850kg (1,873lb) The All-Terrain Hex-Limbed Extra-Terrestrial Explorer (ATHLETE) looks like a shopping trolley gone wrong. The vehicle has six wheels that are fitted to adjustable limbs, so in obstacle-free terrains, it can easily run along. In extreme terrains it can straighten to a height of two metres (6.6 feet) enabling it to walk over obstacles. Prototypes were tested in 2005 with a view to using the concept to carry payloads on the Moon or Mars. Four years later, a second concept, the Tri-Athlete, with three-wheeled limbs was developed. They were intended to be used in pairs so that they could dock either side of a cargo pallet. In Earth gravity it could carry a load of 450kg (992lb) compared to the original's 300kg (661lb).

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Future Tech

Mars explorers

Mars Yard

Take a look at the anatomy of the toughest rovers on Mars Spirit

06

Country: USA Launch date: 10 June 2003 Mass: 185kg (408lb) The six-wheeled Spirit rover carries a suite of scientific instruments including a rock abrasion tool and a microscope at the end of a its robotic arm, enabling the minute examination of Martian rock and soil samples. Mounted on top of a 1.5-metre (five-foot)-tall mast, its pair of panoramic cameras supply high-resolution, colour and stereo images of the terrain to help select areas to explore. The rover transmitted a total of 128,000 images of Mars back to Earth. It carries navigation and hazard avoidance cameras as part of its auto-navigation system, allowing it to move independently and has a rocker-bogie suspension system to cope with 26-centimetre (ten-inch) obstacles. Spirit has been unable to move since 2009 after it got stuck in some soft soil. A year later, NASA lost communication with the rover and it remains silent to this day.

The 21 x 22m (68.9 x 72.2ft) yard simulates the type of conditions rover vehicles will encounter on Mars. Trailers for equipment and researchers are stationed nearby and there is a viewing platform for visitors.

Spirit and Opportunity

Intensive testing for these two vehicles, sent to Mars in 2004, was carried out by this 1.6m (5.2ft)-long Surface System Test Bed rover.

Opportunity

Country: USA Launch date: 7 July 2003 Mass: 185kg (408lb) Opportunity is the twin of Spirit, being part of the overall Mars Exploration Rover Mission to gain knowledge of the Martian geology, its history and whether it ever showed any evidence of the presence of water, now, or in the past. It carries an arm equipped with a range of instruments and power is supplied by solar arrays that feed rechargeable lithium-ion batteries. Radioisotope heaters help keep the rover at optimum operating temperatures. Unlike Spirit, Opportunity continues to communicate with Earth and is still able to move. In July 2014, NASA announced that Opportunity had exceeded the distance of 39 kilometres (24 miles) achieved by Lunokhod 2.

07

Matt Robinson (left) and Wesley Kuykendall (right) show off three generations of Mars rovers that have undergone rigorous testing at NASA's Jet Propulsion Laboratory, Pasadena, California

188

Marie Curie

This is the flight spare (copy) of the Sojourner vehicle (named after the Nobel-winning Polish chemist) taken to Mars in 1997. It is a Robot Wars-sized 65cm (2ft)-long micro rover.

Curiosity

Curiosity

The 3m (10ft)-long Mars Science Laboratory test rover is twice as long as the Spirit and Opportunity vehicles.

08

10 out of this world rovers

Country: USA Launch date: 26 November 2011 Mass: 899kg (1,982lb) Curiosity is the largest, heaviest and most sophisticated robotic rover ever used on another planetary body. Since it is roughly the size and weight of the average car, a unique landing sequence had to be used to get it safely to the Martian surface. A huge parachute slowed it to a speed of 322 km/h (200 mph) and then retrorockets of a sky crane slowed it down before it was dropped on a long tether to the ground. Curiosity has a wide range of tools and instruments, including detectors to study the amount of radiation in the atmosphere and a monitoring station to measure temperature levels, humidity and wind speeds. Its navigation cameras can also be used to study clouds and dust and it has a vast suite of tools to scoop, drill and collect samples that can be analysed by onboard laboratory instruments. It is being used as a test bed for a more advanced Mars 2020 rover mission and is part of the overall goal to send manned missions to Mars in the 2030s.

5 cool things about Curiosity It's a roving papparazzo

Curiosity carries a total of 17 cameras. The Mastcam features two sets of camera systems, one for moderate resolution the other for high-resolution images and video.

It has a powerful laser

ChemCam Uses a laser to zap rocks up to a distance of 7m (23ft) away. A high-resolution camera obtains detailed imagery of the rock and a telescope sends the light from the vaporised rock to three spectrographs to analyse its chemical composition.

It has a robot arm

Curiosity's arm has a reach of 2.1m (7ft) and three joints that are comparable to our shoulder, elbow and wrist joints.

It can ski

The cleated 50cm (20in)-diameter wheels on Curiosity are linked to a rocker-bogie suspension system that can cope with being tilted up to 45-degrees without overturning. The Curiosity rover has a top speed of 0.8km/h (0.5mph).

Radiation-powered

Robot Hand

A radioisotope generator uses the heat from the decay of plutonium-238 to provide power to the rover and to keep its vital electronic systems warm.

Curiosity has a 30kg (66lb) turret hand at the end of its robotic arm, that carries tools and scientific instruments for studying rocks.

Sojourner

09

Country: USA Launch Date: 04 December 1996 Mass: 11.5kg (25lb) Sojourner parachuted to the Martian surface on top the Carl Sagan Memorial Station lander, which deployed giant air bags to cushion the impact of the landing. The micro rover looked like a coffee table with six 13-centimetre (5.1-inch)-diameter aluminium wheels attached to it. Its top speed was an ambling 0.4 metres (1.3 feet) per minute, but it could capably traverse obstacles and soft sand. The table top consisted of solar cells that produced up to 16 watts of power, while further power was supplied by a lithium-thionyl chloride non-rechargeable battery. Two monochrome cameras were mounted on its front and a colour camera on the rear of the vehicle. It remained operational for 85 days, far exceeding its intended seven-day lifespan. It travelled a total of 100 metres (328 feet) and sent back 550 amazing images of the Martian surface.

Mars 2020 Rover

10

Country: USA Launch Date: July/August 2020 Mass: Approx. 1,000kg (2,204lb) Using the sky-crane landing technique to make a precise landing and much of the same hardware as the Curiosity rover, Mars 2020 will be an upgraded version of Curiosity. In light of Curiosity’s findings it will test and use a new range of scientific instruments. It will continue to study chemical reactions and micro-structures to see if Mars ever supported life. In addition, it will obtain soil and rock samples with a view to being collected by future NASA missions. In particular, it will examine the hazards presented by Martian dust storms and wind conditions to future human explorers. It will use experiments to see if it can produce oxygen from the carbon dioxide in the atmosphere for rocket fuel and human respiration.

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Future Tech

Who landed where? Explore the Martian areas these rovers call home Opportunity

Landing site: Meridiani Planum Opportunity landed on the opposite side of Mars from Spirit. The site was chosen because it is a flat plain, which had indications of the presence of hematite, a mineral associated with hot springs and water pools. More by accident than design, it scored a hole-in-one by landing inside the small Eagle Crater. Here it found concretions of hematite nicknamed blueberries. The rover then went on to explore the Endurance Crater, Ersaebus Crater and took a longer 7km (4.3mi) trip to the Victoria Crater before making another journey of 12km (7.5mi) to Endeavour Crater. At one stage it got stuck in a dune and took over a month to get out.

Curiosity

Landing site: Gale Crater The 154km (96mi)-diameter Gale Crater was formed by a meteor strike between 3.5 and 3.8 billion years ago. The explosion sent massive amounts of rock and soil around the impact site and over time the crater was filled with sediments to form the multi-layered Mount Sharp that has been shaped by the Martian winds. The mountain rises to a height of 5.5km (3.4mi). Examination of the rock structures will reveal the history of the presence of any water and if it supported the existence of microbial life. Curiosity’s landing site was named the Bradbury Landing in honour of science-fiction writer Ray Bradbury.

Spirit

Landing site: Gusev Crater Spirit was intended to study the sedimentary material at the bottom of this 166km (103mi)diameter crater that formed between 3 and 4 billion years ago. At some stage, it seems a system of channels fed liquid water or ice into the crater to form a lake. Unfortunately, few suitable rocks were found on the lava plain of the crater, so Spirit was sent on to explore a new area; the low-lying Columbia Hills, about 3km (1.9mi) from the landing site. One of Spirit's wheels stopped working and before it got stuck in some soft terrain, it could only be driven in reverse. In total it travelled a distance of 7.73km (4.8mi).

Timeline of a rover

Discover the exciting history of these rovers Sojourner

4 July 1997 The first rover to be successfully operated on another planet. It was part of NASA’s Mars Pathfinder project to test the viability of a Martian rover.

190

Sojourner

27 September 1997 Final transmission from the rover. During its operation it conducted over 15 chemical studies of rocks and sent back data about Martian weather.

Spirit

6 February 2004 Makes the first drill hole in a Martian rock using its Rock Abrasion Tool (RAT). The rock is analysed by its two spectrometers.

Spirit

5 March 2004 NASA announces that a rock called Humphrey indicates that it was of volcanic origin and might have contained water at some stage.

Opportunity

6 January 2005 Discovers the first meteorite on the Martian surface. Since then, Opportunity has encountered five similar ironnickel meteorites.

Spirit

9 March 2005 Solar panels suddenly become 33% more efficient, cleaned by dust devils blowing over the surface. Dust devils are photographed by Spirit.

Opportunity

26 September 2006 At a distance of 7km (4.3mi) from its landing site, the rover arrived at the Victoria impact crater. It spent two years at this spot enduring severe dust storms.

10 out of this world rovers

Roving records

Sojourner

Landing site: Ares Vallis This area was flooded with water several billion years ago and as a result a huge variety of rocks were deposited here. Sojourner landed at the mouth of this large outflow channel that sent the floodwater into the Chryse Planitia basin. The site was found to be strewn with rocks, the largest being a 2m (3.3ft)-wide rock nicknamed Yogi. A closer and smaller rock, nicknamed Barnacle Bill was the first to be analysed by Sojurner’s spectrometer. Analysis of Yogi indicated that it was more primitive than Barnacle Bill and flood water had probably deposited it there. Their composition indicates that it has a history of volcanic activity.

Which rovers went the distance?

Mawrth Vallis

A proposed site for the Mars 2020 rover and the European Space Agency ExoMars rover missions. An intriguing valley that is on the border between the southern-hemisphere highlands and the northern-hemisphere lowlands. The layers of clay-rich minerals accessible in this region might reveal the ancient presence of life-supporting water.

Key

Moon

Mars KM

10

0

20

30

40

Opportunity USA 2004-Present 42 km

Lunokhod 2 USSR 1973 39 km

Apollo 17, lunar rover USA 1972 35.74 km

Apollo 15, lunar rover USA 1971

Holden Crater

The Holden Crater is part of a string of craters that were connected by rivers of water about 3 billion years ago. It looks, from the deep gullies in the crater wall, that running water filled it to form a lake. Winds have since exposed sediments and rocks that could be the oldest on Mars.

27.8 km

Apollo 16, lunar rover USA 1972

Eberswalde Crater

This is a 65km (40mi)-diameter impact crater that was formed 3.7 billion years ago. It shows evidence that streams of water flowed into it, to form a 115km2 (44mi2) delta. Data suggests that these craters consist of clay, giving further evidence that water has existed here in the past.

26.7 km

Curiosity USA 2012-Present 10.2 km

Curiosity

27 August 2013 For the first time, it plotted a course and travelled a distance of 10m (33ft) using its navigation system. It uses software from Opportunity.

Spirit

1 May 2009 The rover gets bogged down in soft soil and is no longer able to move. On 22 March 2010 it sent its last signals to Mission Control.

Opportunity

Lunokhod 1 USSR 1973

Curiosity

11 September 2014 Reaches Mount Sharp after travelling about 6.9km (4.3mi). This is its prime destination. Here it will investigate its surroundings.

25 January 2014 The 10th anniversary of the rover’s landing on Mars. Rock examinations indicated that Martian conditions were once suitable for microorganisms.

Curiosity

16 December 2014 NASA announces Curiosity detected spikes in methane gas levels in the atmosphere. This could indicate the presence of microbes.

9.93 km

Spirit USA 2004-2010 7.7 km

Sojourner USA 1997 0.1 km

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