Orbiting planets Droids designed by NASA Everything you want to know about our galaxy and beyond EXPLORATION | SOLAR SYSTEM | DEEP SPACE | SPACE SCIEN...
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Everything you want to know about our galaxy and beyond Next-gen space planes Quasars
Orbiting planets
The view from Hubble
Droids designed by NASA
Birth of the Moon
Space elevator
180
pages of amazing facts & stunning images
EXPLORATION | SOLAR SYSTEM | DEEP SPACE | SPACE SCIENCE | FUTURE TECH Interstellar travel
Water on Mars Incredible astronauts
Halley's Comet
Welcome to the
This year we’ve celebrated 10 years of orbiting Mars, as a decade ago NASA’s Mars Reconnaissance Orbiter (MRO) arrived at the Red Planet, and the decision has been made for Dawn to continue orbiting and exploring Ceres. Space exploration is uncovering new wonders with every step. In the All About Space Annual 2017 we take a look at the record-breaking astronauts journeying outside our atmosphere and the planets that make up our Solar System and our cosmic backyard. We journey beyond our home Solar System and even the Milky Way, observing Venus-like exoplanets and Earth’s violent universes. We dive into the depths of worm holes and take a look at some of the incredible experiments that have been conducted on the ISS. Then we look to the future to the incredible technology that we can expect to see in the coming years and theorise how interstellar travel may be developed. 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 Editor in Chief Jon White Production Editor Hannah Westlake Senior Art Editor Greg Whitaker Designed by Jo Smolaga & Alexander Phoenix Photographer James Sheppard Cover images courtesy of NASA, ESO, Thinkstock & 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: Gordon & Gotch Australia Pty Ltd, 26 Rodborough Road, Frenchs Forest, NSW, 2086 Australia Tel: +61 2 9972 8800 Web: www.gordongotch.com.au 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 4 © 2016 Imagine Publishing Ltd 978 1785 464 645
Part of the
bookazine series
Contents 50 Greatest
discoveries pg.8
6
Exploration
Solar System
30 Are we alone in the Solar System?
62 Think you know our Sun? 72 Exploring Venus
38 How we'll find another Earth 46 Record-breaking astronauts
76 Strangest moons 84 Ceres uncovered
52 10 years around Mars
Deep Space
Space Science
92 The hunt for wormholes
116 10 amazing Space Station experiments
100 Violent universe 106 Super Venus
124 Why we live in a multiverse 134 What happened before the Big Bang? 144 Dark energy
158 Next-gen space planes 166 Droids on another world 168 Interstellar travel 174 Space elevator
“In 100 years’ time, human hibernation may be possible, making it easier to send humans to the stars”
© Tobias Roetsch; ESO; NASA; Shutterstock
Future Tech
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The votes are in and counted and now All About Space presents the greatest astronomical discoveries of all time, as chosen by our readers. Some of the greatest moments in space science have come as humans have gazed up to the heavens, sent spacecraft to explore other worlds, and marvelled at how nature has developed this wonderfully complex cosmos that we live in. Science is also a cumulative process, where one discovery leads to another and so on, and astronomy is no different. The discovery that there are galaxies beyond the Milky Way led to the discovery of the expansion of the universe,
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for example. As we run down the 50 greatest discoveries to celebrate All About Space's 50th issue in April 2016, it’s worth remembering all the other discoveries, some of which may have been comparatively small, but all of which played a part in painting our picture of the universe as we know it. So, what has been chosen as the most important astronomical discovery of all time? Could it be the discovery of how stars generate their energy, or how planets are born? Could the discovery and exploration of Pluto be a contender? Or will the latest discovery of gravitational waves pip the others to the title? Read on to find out! www.spaceanswers.com
50 greatest discoveries of all time
49 50
The first galaxy with jets
Light-speed jets, or quasars, were discovered on 16 March 1963 by Dutch astronomer Maarten Schmidt. He had been studying a bright, distant object, which was believed to be a star. But when he measured exactly how far away it was, he was shocked to find that radio Source 3C 273 was 2.5 billion light years from Earth. This was no star, he concluded, as its brightness did not tally with the sheer distance. And so studies into quasars (short for quasi-sellar radio source) began. The greatest puzzle was working out what caused these objects that were more luminous than a galaxy. They knew they were coming from a single place but it took a while to discover they were shining from galaxy cores, only where supermassive black holes were present. Light was unable to escape from a black hole but when material forms a surrounding accretion disc, causes a collision of matter and heats up, jets of high-energy radio waves, x-rays and light waves shoot out. The discovery added evidence to the Big Bang theory.
The discovery of Halley’s Comet
While the discovery of Halley’s Comet is attributed to the English astronomer Edmond Halley, the first record of the passage of Halley’s Comet was actually noted on 30 March 239 BCE by Chinese astronomers in the Shih Chi and Wen Hsien Thung Khao chronicles. The comet also made a timely appearance just before William the Conqueror invaded England in 1066 – a fact that was immortalised on the Bayeux Tapestry. That was
no surprise, though. Halley’s Comet passes by Earth every 76 years or so. As for Edmond? He was the person who correctly computed the comet’s orbit and the first to recognise a comet as periodic. As Savilian Professor of Geometry at the University of Oxford, Halley published Synopsis Astronomia Cometicae in 1705, which stated that the comet sightings of 1456, 1531, 1607 and 1682 were of the same body. By his prediction, the comet
would return in 1758. It was sighted that year and passed perihelion on 13 March 1759. It became known as Halley’s Comet and the calculations have proved to be useful since, not only showing astronomers that a comet can orbit the Sun, but also enabling them to conduct missions and experiments: in 1986, samples were taken of its composition by spacecraft and it was observed through telescopes. Halley’s Comet will next pass Earth on 28 July 2061.
How Halley got its tail
48
2 Forming an envelope 1 Warming the nucleus At this point, the comet is just a lump of ice and rock without a tail, but as it approaches the Sun, it begins to warm up and sublimate.
There is water ice on Pluto A false-colour image map, created by New Horizons and released in January 2016, has shown a greater prevalence of water ice on Pluto than was first imagined, with most of the dwarf planet’s surface appearing to be covered. The maps were based upon data from two Ralph/ Linear Etalon Imaging Spectral Array instruments from a range of 108,000 kilometres (67,000 miles) and while there were some notable gaps – namely at Sputnik Planum and Lowell Regio – the amount of water is stark. According to NASA, “Pluto’s icy bedrock is well hidden beneath a thick blanket of other ices such as methane, nitrogen and carbon monoxide,” which accounts for why a surprising amount of water has emerged within the data.
When the nucleus is 748mn km (464mn mi) from the Sun, it begins to form a coma, a gaseous envelope around the nucleus.
The comet’s orbit Solar wind and radiation causes a tail to form. The tail is made of gas.
Earth’s orbit Earth is at an average distance of 150mn km (93mn mi) from the Sun, known as one astronomical unit (AU).
6 Heading to cooler climes As Halley moves away from the Sun, its tails and gas envelopes disappear.
A comet’s path around the Sun is elliptical. Being a long period comet, Halley takes 76 years to complete one lap around our star and will return on 28 July 2061.
3 Forming a tail
Sun
4 A second tail 5 Sweeping back the gas tail The comet’s gas ion tail is swept back by the forceful solar wind, which causes it to point away from the Sun.
Comets usually have another tail that’s made of dust. This second tail is pushed out by the sunlight.
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50 GREATEST
DISCOVERIES OF ALL TIM E
45 47 The heaviest dwarf planet in the Solar System Discovered in 2003 and confirmed in January 2005, Eris is the most massive dwarf planet in the Solar System. Consideration had been given to Eris becoming the 10th planet, especially as its mass exceeds Pluto’s by 28 per cent, but in the end, both it and Pluto were given the status of dwarf planet. Despite that, Eris’ significance is not in doubt. The very fact that Eris and Pluto were reclassified was down to Eris. It had sparked a debate over what should and should not be a planet, which was settled only by an official definition being drawn up by the International Astronomical Union.
That led to an entirely new category, while it in no way lessened the importance and excitement over the latest discovery (nor, come to that, of Pluto as New Horizons has shown). At first, Eris was seen to be the second largest dwarf planet in the Solar System after Pluto, but observations now show that Eris is roughly the same size as Pluto, with a diameter of 2,326 kilometres (1,445 miles) while Pluto’s is around 2,300 kilometres (1,429 miles). Just to spice things up, Eris has a moon, too – Dysnomia. It’s one of the few dwarfs to have one.
46 The very first object beyond the orbit of Pluto Although Pluto was discovered in 1930 and the first of its five moons, Charon, was found on 22 June 1978, the first object found beyond Pluto’s orbit proved to be one of many. Astronomers David Jewitt and graduate Jane Luu had been searching the outer Solar System using various telescopes for five years. They were looking for evidence of a trans-Neptunian population of objects – now known as the Kuiper Belt. In 1992, their efforts were rewarded when they found an object orbiting the Sun beyond Pluto and named it (15760) 1992 QB1. The following April, they
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wrote a letter to the journal Nature in which they said it “may suggest the first detection of a member of the Kuiper Belt.” They were correct, for (15760) 1992 QB1 became just one of many such objects found in the region. Of course, the repercussions of this find would later be felt. Over 1,000 objects have been found in the Kuiper Belt and there are said to be tens of thousands more. Eris has become the largest known trans-Neptunian object in the belt which, ironically, led to Pluto being downgraded from planet to dwarf planet in 2006.
Rings are discovered around Saturn There is little doubt that astronomer Galileo Galilei contributed greatly to our understanding of space. In 1610, he observed the rings of Saturn, although he believed at first that it was a bright star flanked by two dimmer ones. Two years later, he saw the rings edge on and exclaimed shock that they had apparently disappeared. Four years later still – having let out a sigh of relief at their return in the meantime – he believed the rings to be a pair of half-ellipses. Saturn’s phenomena gripped astronomers who found the sight mesmerising, unique and unusual. Christiaan Huygens proposed the ring was solid in 1655 and that stuck until 1856 when theorists began subscribing to the idea that the ring was actually made up of particles, a hunch the robotic space probe Pioneer 11 would verify in 1979, and which had actually been suggested in 1660 by Jean Chapelain but ignored. Pioneer 11 passed by Saturn at a distance of 21,000 kilometres (13,050 miles) from the planet’s cloud tops and it sent back some stunning images. Shortly after, the Voyager 1 and Voyager 2 spacecraft completed their own missions around Saturn, showing billions of ring particles that ranged from tiny particles the size of dust, to some as large as mountains, each likely to be fragments of asteroids, comets or moons which broke up as they got close to Saturn. Two small moons were also found to orbit within gaps in the ring and it was discovered that the rings – at one kilometre (0.6 miles) thick – orbit at different speeds. In 2009, a huge new ring was found distantly orbiting Saturn. Researchers say it is nearly 7,000-times larger than Saturn itself and is most likely made up of debris from Saturn’s distant moon Phoebe.
50 greatest discoveries of all time
44
Detection of cosmic neutrinos Neutrinos are high-energy subatomic particles that lack any charge and are difficult to detect. They are produced through the interaction between cosmic rays and their surroundings and were detected in 1987, sourced back to a supernova explosion in a nearby galaxy. In April 2012 researchers at the IceCube Neutrino Observatory in Antarctica detected two neutrino events above 1 petaelectronvolt. The neutrinos had been scattered towards our Solar System following a supernova in the Large Magellanic Cloud. To be absolutely sure, the detector was activated once more and 35,000 neutrinos were recorded – 21 of which were of sufficient energy to have come from outside of the Solar System.
Cassini Division Encke Gap
s, Telesto and Callisto Tethy
Enceladus
Mimas
Pan
eus and Janus Epimeth Pandora
Atlas Prometheus
Roche Division
Saturn D
B
A F
G
E
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50 GREATEST
DISCOVERIES OF ALL TIM E
43 Discovery of Uranus While we now know where Uranus is in the night sky and can, with good conditions, see it with the naked eye, it took until 1781 for the planet to be discovered. Amateur astronomer Sir William Herschel spotted it by accident on 13 March while he was using his self-designed telescope to survey magnitude eight stars (those too faint to be seen with the eye alone). Sitting alone in his garden in Bath, England, he recorded an object that, on a subsequent scan of the sky, had changed place and appeared to be closer than the star field. Everyone who had seen Uranus had assumed they were gazing at a star. Herschel believed it to be a comet.
This baffled his fellow astronomers. They pointed to a lack of a coma and said a comet that bright would be moving more quickly. When astronomers began to look more closely at the object’s orbit (not in its entirety, it has to be said, since it takes 84 years to complete one), they were able to conclude only one thing: that it had to be a planet, the seventh to be spotted in the Solar System. In 1783, Herschel wrote to the Royal Society president Joseph Banks and confirmed that he too believed it to be “a Primary Planet of our Solar System,” and so it became the first to have been discovered with the aid of a telescope. Uranus’ rings were discovered in 1977.
42 The Sun has a fiery solar wind Solar flares – a sudden release of electromagnetic radiation – were observed in 1859 by astronomers Richard C Carrington and Richard Hodgson but it would later be found that they were not the only events occurring close to the Sun’s surface. Geomagnetic surveys carried out by Kristian Birkeland showed almost uninterrupted auroral activity and in 1916, he suggested that solar rays consisted of negative electrons and positive ions. It lent weight to a theory that British astrophysicist Arthur Eddington had skirted with in 1910 – that there was a near continuous and multidirectional outflow of gas from the Sun. That was confirmed in 1959
when the Soviet craft made the first ever direct observations and measurements of the solar wind, noting the charged particles that were being emitted. We now know that this happens because the corona, the final layer of the Sun’s atmosphere, heats to as much as 2 million degrees Celsius (3.6 million degrees Fahrenheit), which weakens the Sun’s gravitational pull on the particles and allows them to stream away. Where there are coronal holes there is higher solar wind velocity. All of this would cause damage to Earth was it not for the shielding magnetic field around our planet, which directs the particles away.
41 Stars explode with exotic gamma rays Gamma ray bursts were discovered in 1967 by the Vela satellites, which were sent into space to detect covert nuclear weapons tests. Even though the bursts can last for as little as a fraction of a second to just a few minutes, it became apparent after years of study that the intense beams of radiation were not only coming from other galaxies, some of which are very distant, but appeared to occur when stars exploded at the end of their lives. When a massive star, many times the mass of the Sun, runs out of fuel, collapses under its own weight and creates a black hole, some energy is released as highly-focused gamma rays
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– the most powerful form of radiation – that breaks free in opposite directions from the star’s north and south poles, before driving through the cosmos at close to the speed of light. The star later explodes as a supernova. In 2013, astronomers discussed three unusually long-lasting stellar explosions that produced highenergy emissions for hours. It was envisioned that it came from a star similar in size to the Sun but around 20 times its mass. One seven-hour gamma ray burst was thought to have marked the death of a blue supergiant that contained modest amounts of elements that are heavier than helium.
50 greatest discoveries of all time
40 There are lakes and seas on Titan There had already been a theory in the late 1960s that Titan would have seas and lakes, but it took data from Voyager 1 and 2 and direct evidence from the Hubble Space Telescope in 1995 to begin affirming those hunches. Even so, when Cassini-Huygens unmanned spacecraft launched in 1997, the information it would yield would blow astronomers away. Huygens was the first probe to land on Saturn’s moon, touching down within a dry plain in 2005 and giving astronomers their first taste of their target world. The rounded rocks showed that some kind of fluid had once flowed there but it was data from the Cassini orbiter that was most remarkable, uncovering methaneethane lakes and the river channels that feed them. None of the lakes could possibly hold flowing water, the -180-degreeCelsius (-292-degree-Fahrenheit) conditions on Titan forbids that, but
38 What space
objects are really made of
there are water-like cycles of the type we see on Earth with methane evaporating into the atmosphere where it is converted into ethane by sunlight. The lakes and seas are also mappable. With more in the north than in the south, hundreds have been
observed so far and each of them has been given a name. Who knows, as one of the least hostile bodies in the Solar System and talk of humans perhaps one day living there, maybe they’d be the perfect place to take out a boat. Or not, as it is more likely.
39 A baby planet in the process of forming
We have long known about the spectral nature of light: Isaac Newton showed in 1666 that the Sun’s white light could disperse into a series of colour when shone through a prism, or the spectrum, as he called it. Yet things became very interesting when it was discovered that the energy given off by matter also emits light, and that by using heat it was possible to break down chemical bonds and study the resulting spectrum for small amounts of an element. This was made possible because of the way dense gases or solid objects radiate heat through light production. This discovery has, therefore, been successfully applied to space objects. Scientists have been able to use line spectra to discover new elements such as rubidium, which would not otherwise have been spottable. It has also allowed scientists to figure out the composition of the Sun by studying the absorption lines in its spectrum. This led to some fundamental discoveries including the finding of helium at 587.49 nanometres in the spectrum of the Sun.
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As astronomers Adam Kraus and Michael Ireland looked through the Keck II telescope in 2011, they saw an exoplanet called LkCa 15 b, located 450 light years away in the Taurus-Auriga star forming region. Not only did they note it was the size of Jupiter, they saw it in the process of active accretion – the first time such a thing had ever been observed. It was a remarkable discovery, made all the more amazing four years later when it was captured in an image via the Large Binocular Telescope and the Magellan Adaptive Optics System in Arizona. Astronomers hope it will allow them to learn more about how baby planets formed, making
for more accurate estimates of the age of other forming systems. The planet orbits a star known as LkCa 15 which is just 2 million years old. Scientists have also been able to discover the chemical footprints of superheated hydrogen gas coming from the protoplanetary disc that forms around young stars, with Stephanie Sallum, a University of Arizona astronomy graduate, saying it provided the first opportunity to directly study planet formation and discplanet interactions. As the planet grows and potentially creates rings and gaps, astronomers will be able to discover much more about the early years of formation.
The discovery of space magnifying glasses After years of theorising, the universe was finally found to have a cosmic magnifying glass in 1979 when a team led by Dr Dennis Walsh of the University of Manchester’s Jodrell Bank Observatory discovered the first example of a gravitational lens. Dr Walsh was studying quasars and saw that the light from one object was being deflected around a closer object. It made the faint quasar appear brighter and more visible, an effect that has since allowed astronomers to look farther into space and enabled the study of brown dwarfs, red dwarfs, black holes and planets around other stars. It’s also proven very useful in the search for dark matter.
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50 GREATEST
DISCOVERIES OF ALL TIM E
36 The early Solar System was bombarded with thousands of space rocks The Solar System began to form about 4.6 billion years ago in a wispy cloud of gas and dust. A relatively short time later – between 4.1 and 3.8 billion years ago – a large number of asteroids are said to have collided with the early terrestrial planets, causing mammoth craters in many of the newly formed bodies. Thought to be caused by Neptune being catapulted outwards and colliding with a ring of comets
(the Nic model posits orbital migration of the gas giants), this has been called the Late Heavy Bombardment and it was a time of utter galactic chaos. Evidence for this was discovered in lunar samples brought back by Apollo astronauts, but although this was a period of intense turmoil for the early Solar System, it would also appear that around the time the Moon was formed 4.5 billion years ago, the Solar
System was also blitzed by thousands upon thousands of tiny space rocks, or planetismals. This, according to researchers at Massachusetts Institute of Technology in December 2014, kicked up clouds of gas here on Earth and led to the permanent ejection of small portions of the atmosphere into space. It may well have done the same for the atmospheres of Venus and Mars, too.
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Stars can orbit black holes In 2013, a red dwarf star with a mass one-fifth that of the Sun was seen to orbit a black hole named MAXI J1659-152 once every 2.4 hours, travelling at 2 million kilometres (1.2 million miles) per hour. Black holes have long been known to have mass, which causes a gravitational force affecting objects nearby. This was seen within the binary star system Cygnus X-1, discovered in 1962. While faint blue, supergiant primary star HDE 226868 emitted visible light, its companion did not and it was later concluded that HDE 226868’s 5.6-day orbit was actually around a black hole.
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35 Ice giant Neptune is found Astronomer Galileo Galilei observed Neptune in 1613 but is said to have dismissed it as an 8th magnitude star and put it to the back of his mind. French mathematician Urbain Le Verrier was asked to look into the problem of why the astronomical observations of Uranus showed an orbit at odds with Newton’s laws of gravity. Uranus, discovered in 1781, was being pulled slightly out of its orbit and Le Verrier concluded on 1 June 1846 that it must be due to the influence of another planet further away from the Sun. He calculated where in the sky this planet should be and asked Johann Gottfried Galle at Berlin Observatory to search for it. On 23 September 1846, Galle located it, one degree away from where Le Verrier said it would be. It was the last true planet to have been discovered in the Solar System.
33 There are magnetic space bubbles beyond the Solar System Voyager 2 and Voyager 1 set off on their respective journeys to study the Solar System in August and September 1977 but they continue to shed new light on the universe even today. Having now travelled farther than any object in history, they have been able to make some extraordinary discoveries in farflung locations, with one discovery taking place on the edge of the heliosphere in a region called the heliosheath. The heliosheath acts as an effective border between the Solar System and the rest of the Milky Way and the probes, to the surprise of scientists, began to measure abrupt changes in the flow of particles within that space as they glided 14.4 billion kilometres (9 billion miles) from Earth in 2007 and 2008. Scientists discovered that Voyager 1 and Voyager 2 were
also seeing different changes at different times, which proved rather puzzling. To explain this, they theorised that the Sun’s magnetic field was extending to the edge of the Solar System and that, since the Sun spins, the field was twisting and reconnecting. Computer simulations then found that, as a result of this, the probes were actually travelling through huge bubbles 170 million kilometres (100 million miles) wide and, as each one entered and exited a bubble, they were measuring sudden changes. It was an eye-opening discovery and it has led to many suggestions for the use of the magnetic space bubbles. One of the most favoured suggestions was put forward by Merav Opher, of Boston University, who believes that the bubbles trap cosmic rays and so act as a first line of defence.
50 greatest discoveries of all time
32
The crater that points to the extinction of the dinosaurs
Question marks have hung over the fate of the dinosaurs for decades but it now seems more likely that it was caused by the impact of a 9.7-kilometre (sixmile) wide asteroid or comet. Scientists Luis and Walter Alvarez first made the suggestion in 1980 and further research pointed to a 177-kilometre (110-mile) wide crater off the Yucatán coast of Mexico in Chicxulub. The theory became known as the Alverez hypothesis. Despite this, there had been some doubt. It appeared that the cosmic impact had taken place many tens of thousands of years before or after the dinosaurs became extinct. This uncertainty prompted scientists in 2010 to embark on a three-year study to find the exact date that the asteroid or comet
hit. They based it on the radioactive decay of argon and found that it happened 66,038,000 years ago, give or take 11,000 years. What’s more, the impact and the extinction were as little as 33,000 years apart. Any impact of this magnitude – the comet or asteroid is likely to have unleashed 1 billion times more energy than the atomic bombs dropped on Hiroshima and Nagasaki in 1945 – would have covered the Earth with life-sapping dust and noxious fumes. But last year, evidence pointed to the situation having been made worse due to the fact the impact triggered huge volcanic eruptions at the Deccan Traps in India. The key now is to prevent the same thing from happening to us.
31 The heaviest stars in the universe explode When the nuclear furnace at the core of a star runs out of fuel, those which are more than eight times the mass of the Sun violently explode in dramatic style. These type II supernovae begin to swell, ejecting material outwards at great speeds until they blow, leaving behind a collapsed central core that becomes either a neutron star or a black hole. But why does this happen? Hydrogen fuel begins to run out within the star, causing its expansion and producing an ever-hotter core, which begins to use helium to make carbon and oxygen. Nuclear reactions create elements that are increasingly heavy and the core builds up with iron and becomes unbalanced. As the nuclear fusion reactions cease their outward push of pressure, it exerts so much gravity that it pulls the star inwards. When the iron core collapses, the star explodes. We’ve known about supernovae since 185 CE – when supernova SN 185 was observed by Chinese astronomers – but we began to find out more about which red giant stars exploded and which did not due to Fred Hoyle’s concept of nucleosynthesis from 1946.
29 Europa has an underground ocean Evidence that Europa has an ocean beneath its icy shell began in the 1960s when it was observed that its surface composition was mainly water ice. The flybys of Voyager 1 and 2 in the early 1970s allowed for detailed imaging of the moon, while the 1989 Galileo mission revealed Europa’s magnetic field was disrupted, indicating a deep layer of electrically conductive fluid. Today we believe the moon’s On 1 January 1801, Sicilian astronomer ocean could run as deep as 100 Giuseppe Piazzi saw a faint object that would keep kilometres (62 miles) and there may astronomers busy for a further 215 years. At first Piazzi be twice as much water on this thought the body was a fixed star until he saw that it small body than on the whole of moved. He then concluded that he was actually staring Earth. There is evidence that the at a planet 4.8 million kilometres (3 million miles) away moon’s smooth surface is a result in the space between Mars and Jupiter. Other bodies of a fascinating “healing” process – were found in the same region, adding Pallas, Juno after comets and meteorites hit, the and Vesta to a group of what would come to be underlying water rises to the surface called asteroids. Seen as round by Hubble and freezes in temperatures as low and emerging as the largest body in the as -160 degrees Celsius (-256 degrees asteroid belt, it was promoted to Fahrenheit). A mission to explore dwarf planet in 2006. Europa is due to launch in 2022.
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Dwarf planet Ceres is found
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50 GREATEST
DISCOVERIES OF ALL TIM E
28
Rockets work in a vacuum
Isaac Newton’s third law of motion says that every action produces an equal and opposite reaction, and it was with this firmly in mind that Robert Goddard realised rockets would work perfectly well in the vacuum of space. The accepted wisdom was that a rocket would need air against which it could react but Goddard worked out a system that would adhere to the relation of action to reaction by allowing the rocket’s engine to work against itself. In 1912 he explored the use of rocket propulsion to reach high altitudes, eventually devising the rocket engine, which only needed enough solid or liquid fuel to push on the exhaust with enough power to propel it forward. It’s a very different way of working
when compared to a jet engine, which needs air, and while the principle behind this was actually used some centuries before Newton was actually born (NASA says rockets were used in China in the 1200s for fireworks but they were, of course, not being shot into space), Goddard’s method proved to be revolutionary. Goddard constructed and tested a liquid fuel rocket on 16 March 1926 with the fuel burned and hot exhaust gases expelled at high velocity, and he outlined his intentions of producing a rocket that would be capable of reaching the Moon should it be required. He shot a scientific payload in a rocket flight in 1929 but, more importantly, helped pave the way for space exploration.
Rockets of the 21st century >100
Payload (per 1000kg)
30 25 20 15 10 5 0
Titan II
Proton
1964-1966 1965-Present 3,100kg 20,700kg
16
Saturn 1B Titan IIIB Saturn V
STS
Titan IV
Delta II Ariane IV
Atlas II
1966-1987 3,300kg
1981-2011 24,400kg
1989-2005 17,000kg
1989-2011 1990-2003 5,089kg 7,600kg
1991-2004 6,580kg
1966-1975 21,000kg
1967-1973 127,000kg
Ariane V
Atlas III
1996-Present 2000-2005 21,000kg 8,640kg
50 greatest discoveries of all time
27 How the Moon was made First of all, the Moon is not made of green cheese, contrary to the popular proverb from 16th and 17th century English literature. As of 2001, the giant-impact hypothesis, proposed in the 1970s, has emerged as the most likely explanation of how the Moon was made. It says an embryonic world called Theia, which grew to the size of Mars, formed in the same orbit as a protoplanetary Earth but, due to its size and mass, eventually crashed into our planet at an oblique angle around 4.5 billion years ago. It not only destroyed Theia but it carved
away a portion of the Earth’s silicate mantle. As the pieces made their way into outer space, gravity caught hold, bringing the debris into Earth’s orbit, mixing them together into clumps. Eventually a body the size of the Moon was created. In 2014, and in support of this theory, Daniel Herwartz of the University of Göttingen and his team looked at lunar rocks collected by Apollo astronauts and found that differences in the isotopic makeup of Earth and the Moon pointed to the latter being made of 40 per cent Theia.
26 Enceladus shoots geysers
Atlas V
Delta IV
Delta IV
Falcon 1
Vega
Falcon 9.1
2002-Present 2003-Present 2006-2009 2012-Present 2013-Present Heavy 12,500kg 9,420kg 180kg 1,500kg 13,150kg 2004-Present 28,790kg
The unmanned Cassini spacecraft, which was sent on a seven-year journey to Saturn in 1997, first spotted geysers on the moon Enceladus in November 2005. Liquid water reservoirs were seen to erupt from four linear depressions in the body’s south polar region, known as tiger stripes. These icy jets were ejecting particles at high speed, causing excitement among scientists, as it broadened the diversity of potential life-sustaining environments within the Solar System. Since that observation, evidence has emerged pointing to the geysers extending down to an ocean of salty
liquid water beneath the moon’s icy shell. Indeed, a seven-year study culminating in 2014 identified 101 distinct geysers erupting from the tiger stripe fractures. And since they were coincidental with small hot spots of the right size to be the result of condensation of vapour, it pointed to them having deep roots. Interestingly, output from the geysers has been found to have fallen by as much as 50 per cent over the past 10 years, opening up a new mystery. We're soon to find out more as Cassini flew through the geysers in October to collect samples and images.
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50 GREATEST
DISCOVERIES OF ALL TIM E
25 Discovery of Pluto
24
The universe is dying After measuring the energy of 200,000 galaxies, astronomers came to a startling but depressing conclusion: the universe is slowly dying. The energy today, they found, is half of what it was 2 billion years ago. According to astronomers of the Galaxy and Mass Assembly Project (GAMA), the fading has been occurring across 21 wavelengths, from ultraviolet to the far infrared. The problem has arisen as the energy-making process of the stars, which convert their mass into energy as noted in Einstein’s equation E=mc2, has been diminishing. Head of the GAMA team Simon Driver, predicts: “The universe will decline from here on in, sliding gently into old age.”
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American astronomer Percival Lowell had predicted the existence of a planet beyond Neptune in 1905 but it would not be until 1930 that proof of the so-called Planet X was finally found. The previous year, Clyde Tombaugh, a young researcher, had impressed bosses at the Lowell Observatory with his detailed drawings of Jupiter and Mars and ten months later, he struck gold. Tombaugh had been tasked with using a 13.9-inch astrograph to take photos of the same section of sky several nights apart. He then used a blink comparator, a piece of viewing apparatus used to discover the differences between two images of the night sky – a technique which, on 18 February 1930, allowed him to finally spot a planet-like body. The discovery was announced three weeks later, on 13 March, and the name Pluto – suggested by an 11-year-old schoolgirl called Venetia Burney – was adopted on 1 May. It was greeted with widespread excitement as astronomers looked to find out more about this mysterious planet and look for evidence of more bodies, and it eventually led to the ground-breaking New Horizons mission. Despite that, Pluto was re-classified as a dwarf planet by the International Astronomical Union in 2006, following the 2003 discovery of Eris and the observation of other smaller-sized bodies in the Kuiper Belt. That put the number of planets back down to eight but Caltech astronomer Mike Brown has recently put forward evidence for a replacement that he is calling ‘Planet 9’.
23 Stars make radio waves When Karl Jansky was tasked with using his radio receiver to study radio frequency interference from thunderstorms, he thought he would only discover what was causing such great interference with his employer’s transatlantic transmissions. Never in his wildest dreams did he think that his experiments in 1932 at Bells Telephone Laboratories would make him the original “radio star”. His initial findings had confirmed some hunches: much of the static was indeed attributable to the storms near and far. But the existence of some extra background noise was proving harder to explain. He studied this long and hard and realised that it seemed to be coming from the Sun. It followed, what appeared to be, a 24-hour cycle or, to be exact, a cycle of 23 hours and 56 minutes. Since this was a characteristic of fixed stars, it led to a startling conclusion. Jansky realised that the radiation was actually coming from the centre of Milky Way and that stars were emitting energy in the form of not just light waves, but radio waves. Still, his findings were largely ignored. It took fellow engineer Grote Reber to pick up the discovery using a 9.6-metre (31.4-foot) diameter telescope for it to be recognised.
22 Stars are powered by fusion Unconvinced that the Sun was a simple roaring ball of fire, the English astronomer, physicist and mathematician Arthur Eddington proposed that stars were actually powered by fusion. He said the fusing of small nuclei to produce large amounts of energy provided the energy source that powered the stars. He went on to explain that the Sun was able to shine by converting hydrogen atoms to helium, and that it would allow the Solar System’s star to shine for 100 billion years before the fuel for this energy ran out. Over the years, scientists have built upon this theory and it is now
accepted that the Sun has a dense and highly-pressurised core within which hydrogen atoms smash into each other at speed, fusing the nuclei to produce heat and helium. This sends energy outwards, causing photons to bounce around the Sun’s 289,000-kilometre (185,000-mile) thick radiative zone before making their way to the convective zone where they move along to the surface. Only when the hydrogen begins to run out do other fusion reactions take place and this leads to a change in the star: when the nuclei of elements heavier than iron are formed, for instance, supernovae are created.
50 greatest discoveries of all time
21Higgs boson
Discovery of the
For 45 years, physicists searched in vain for the elusive Higgs Boson, the 17th piece of the Standard Model of theoretical physics, which rules how particles that make up all of the atoms, molecules and matter of the universe should interact. Cern scientists went to extraordinary lengths to work out how the particles gained their mass, going as far as building the 27-kilometre (16.8-mile) long Large Hadron Collider (LHC) some 100 metres (330 feet) beneath the French/Swiss border. But while it took around a decade to complete and cost $4.75 billion (approximately £3.39 billion), on 4 July 2012, it yielded the result they had been hankering for.
The LHC is a particle accelerator containing 9,300 magnets cooled to -271.25 degrees Celsius (-456.25 degrees Fahrenheit) and capable of smashing two beams of protons together at close to light-speed. By creating large numbers of particles during this crash, physicists wanted to see a trail of evidence pointing to the existence of Higgs – proposed, incidentally, by Peter Higgs in 1964. The data showed evidence of a particle weighing 125.3 gigaelectronvolts, meaning its mass is 133 times that of a proton. It pointed to the discovery of a new particle, and while there is still much work to do, it has brought us closer to unlocking the secrets of the universe.
What is the Higgs boson? Finding the Higgs explains how particles in the universe acquired mass after the Big Bang. Two types of particle comprise the cosmos, which are governed by fundamental forces
Bosons Bosons, which are protons, Z bosons, etc, give rise to the forces that affect fermions
Fermions This type of particle is the building block of matter and encompasses electrons, down quarks, etc
Atom
Nucleus
All matter is made of atoms.
The centre of an atom, comprised of positive protons and neutral neutrons.
Matter
Photon
W and Z bosons Gluon boson
Graviton boson
Photons are responsible for electromagnetic force and transmit light.
These bosons are responsible for the weak force, which causes particles to decay and change.
This boson still needs to be found. The graviton is responsible for gravity.
The Gluon causes the strong force, which keeps an atom’s nucleus together.
Sub-atomic particles often vary in mass, thanks to collisions with the Higgs boson
Electron
Protons and neutrons
Subatomic particle with a negative elementary charge, which orbits the nucleus.
These subatomic particles are comprised of up and down quarks.
Up and down quarks
Photon
Electron
Down quark
0 mass
0.0005 GeV
0.01 GeV
GeV = Gigaelectronvolt
Z boson 91 GeV
Particles not to scale
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50 GREATEST
DISCOVERIES OF ALL TIM E
20
Our galaxy is a spiral shape
One of the problems with mapping the Milky Way is that we are inside it, making it difficult to get an overall picture of its shape. But when Harlow Shapley studied globular clusters – spherical collections of stars – he began to form a picture of the overall shape of our galaxy. As time went on and radio telescopes, which could penetrate dust, became widely used, it would be discovered that our galaxy was spiral rather than elliptical as was first thought. As well as putting the Milky Way in the same pot as two-thirds of all known galaxies, the studies also showed that Earth was about two-thirds of the way out from its centre.
But we still don’t know everything about the specifics of the spirals. Only in 2005 did observations from the Spitzer Space Telescope confirm the Milky Way was a barred spiral galaxy, which means that it has a rectangular block of stars at its centre rather than a sphere. And only last year did more of the blanks of the spiral map of the Milky Way begin to be filled. Data from NASA’s Wide-field Infrared Survey Explorer found more than 400 dust-covered nurseries of stars tracing the shape of the spiral arms. This, says NASA, supports the four-arm model of the Milky Way’s spiral structure and it’s within those arms that most stars in the galaxy are born.
18 There are active volcanoes on the surface of another world
19 The Earth is round The idea of a spherical Earth dates back to Ancient Greece and is typically credited to Pythagoras who made his discovery having observed lunar eclipses in the 6th century BCE. Since then – and with the belief that Earth was flat dispelled – the spherical nature of Earth has been documented many times over the following centuries. It’s allowed us to better understand our planet and explore Earth and space more effectively, as scientists can better devise their theories before venturing skywards in a bid to confirm their validity. Of course, once astronauts viewed Earth from the height advantage of a spacecraft, the theory of a round planet was proven to be entirely correct. Yet, interestingly, we’ve come to realise our planet is an irregularly shaped ellipsoid with a bulge at the equator.
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Linda Morabito began work at Jet Propulsion Laboratories in 1974 but her opportunity of a lifetime came five years later when she became the cognisant engineer of the Optical Navigation Imaging Processing System, where she assisted in the navigation of Voyager 1. On 9 March 1979, she was processing images from the craft and spotted a large crescent-shaped anomaly just off the rim of Jupiter’s moon Io. Investigating deeply, she believed that what she was seeing was consistent with volcanic activity. The
following Monday, it was confirmed. The image was a 270-kilometre (170mile) tall cloud and it was the first time active volcanism had been detected outside Earth. Today there’s absolutely no doubt that Io has volcanoes. Each time a spacecraft has passed, volcanoes have been observed. We now know Io has over 150 active volcanoes, with predictions of around 400 in total. Yet it is by no means unique. Saturn’s moon, Enceladus and Neptune’s moon, Triton are also volcanically active.
17 Finding the most Earth-like planet The number of known planets in the universe exceeds 1,700, although a computer simulation run by astronomer Erik Zackrisson from Uppsala University in Sweden, shows there could be as many as 700 quintillion planets in the universe. Of those, he says, there could be none exactly like Earth but astronomers have, to date, found some Earth-like planets. In 2007, a planet orbiting the star Gliese 581 some 20.4 light years away, was discovered to be the first superEarth. Although it was greeted with some doubt it caused excitement. As an
exoplanet of terrestrial mass thought to orbit within the star’s habitable zone, the so-called Gliese 581d was found to have a mass seven times that of Earth and, in theory, it could have an atmosphere and liquid ocean. More recently, evidence has built up that shows it could exist, and it’s important to establish the truth of this planet because the find was a benchmark case for the Doppler technique – the indirect method used to find extrasolar planets by analysing the motion and properties of the star and planet.
50 greatest discoveries of all time
Galaxies of all shapes and sizes Lenticular galaxies These intermediate galaxies are between the elliptical and the spiral. They have a bulge, but no spiral structure.
S0
E0
E3
E5
E7
Sb Sa
SBa
Elliptical galaxies Ellipsoidal in shape, these galaxies are 3D in shape. They are the most abundant type of galaxies in the universe. The lower the number, the more spherical the galaxy.
Sc
Spiral galaxies The spiral galaxy consists of a flat rotating disc of stars, gas and dust as well as a central concentration of stars known as the bulge. Spiral galaxies can be found to have a bar, which appears to lace through the centre and link the arms.
SBb
SBc
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Part of the universe is missing In 1933, Swiss astronomer Fritz Zwicky correctly argued that what we could see in the universe wasn’t quite everything that was there. In his study of the Coma Cluster in the 1930s, he noted the rapidly-moving galaxies did not have enough visible matter to provide the necessary gravity to hold them together, and so looked to discover what was keeping them from tearing apart. His studies were not immediately seized upon until astronomer Vera Rubin was measuring the velocities of stars in other galaxies in the 1970s. She found that single galaxies as well as clusters also had hidden mass. Rubin believed something else must provide the gravity. That something is dark energy and dark matter that, combined, form a staggering 96 per cent of the universe (with everything that we can see making up the remaining four per cent).
16 The first pulsating star
Pulsating stars first came to light in the dead of night on 28 November 1967 but the discovery was to go on to be mired in controversy. Student Jocelyn Bell Burnell was the “star pupil”, being the first to observe and precisely analyse the pulsars. Bell Burnell’s discovery was extraordinary. What she had seen were unusual radio pulses emanating in rapid, regular bursts from a single point in space. After a month of work and attempts to figure whether there was something wrong with the telescope, a second pulsar was found. It was concluded that they were highly magnetised rotating neutron stars formed from the remains of massive stars after they had exploded into supernovae. They provided the first evidence that Albert Einstein’s theory of gravity was correct.
14 Discovery of the first supermassive black hole In the centre of massive galaxies are supermassive black holes that most likely formed from the collapse of huge clouds of interstellar gas. As with “regular” black holes, which have a mass of up to 20 times that of the Sun, gravity pulls so strong that even light is unable to get out. The big difference is that supermassive black holes can have a mass equivalent of as much as 100 million Suns. In 1971, Martin Rees and Donald Lynden-Bell, astronomers at the University of Cambridge, hypothesised the existence of a supermassive black hole hiding in the centre of the Milky Way. Three years later, American astronomers Bruce Balick and Robert Brown discovered a compact and variable radio source in the heart of Sagittarius A, which they named Sagittarius A*. It was a remarkable discovery pointing to evidence of a supermassive black hole in that location and, since then, it has been conclusively shown to be the galactic centre around which the rest of the galaxy rotates.
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50 GREATEST
DISCOVERIES OF ALL TIM E
12 13 A galaxy straight after the Big Bang When we look into the night sky, the galaxies that can be seen are a glimpse into the past. The light from them takes billions of years to reach us so it is possible to discover and observe primordial galaxies very close to the Big Bang (in relative terms, at least). In May 2015, a galaxy named EGSzs8-1 was found at Boötes and it was thought to be the most distant and oldest of all the observed galaxies. Yet just two months later, another galaxy – EGSY8p7 – was observed. The light from this galaxy had taken 13.2 billion light years to reach Earth. It means that the mass of stars being observed existed just 600 million years after the Big Bang, a figure based on our current understanding that the universe is 13.82 billion-years-old.
The Earth has a magnetic field
The effects of the Earth’s magnetic field have been known for more than 2,000 years, although it was some time after that when scientists figured out that the power was coming from convection currents produced by the churning motions of hot iron liquid at the planet’s core. Without the magnetic field, there would be no way of deflecting the charged particles streaming out of the Sun in the form of the solar wind. The magnetic field, therefore, offers Earth’s atmosphere muchneeded protection. In 1906, our knowledge of the Earth’s magnetic field took a step forward. French geologist Bernard Brunhes had been studying samples of volcanic rocks taken from a sparsely populated region of France called the Auvergne. When he tested those rocks, he noticed some of them contained iron particles, which had magnetised in the opposite direction to the current pole when the lava cooled. Knowing that molten lava preserves a snapshot of Earth’s polarity when it cools, it led to the discovery that the Earth’s magnetic
field can flip. North had become south, and it turned perceptions of our planet on its head. The Earth is said to flip its poles every few hundred thousand years, although at some point in the distant past it was flipping every five million years – it last happened 780,000
years ago. There’s a chance it could happen in our lifetime as the magnetic field has been fading for 200 years – a sign that it could collapse and reverse. If it does, the weakened geomagnetic field could adversely affect power grids and the navigation of animals.
North magnetic pole
Geographic North Pole
At this pole of Earth’s Northern Hemisphere, the planet’s magnetic field points vertically downwards.
The point in the Northern Hemisphere where the Earth’s axis of rotation meets its surface.
Poles apart The geographic and magnetic poles are separated by an angle of around 11.5°.
Geographic South Pole The point in the Southern Hemisphere where the Earth’s axis of rotation meets its surface.
South magnetic pole At this pole of Earth’s Southern Hemisphere, the planet’s magnetic field is directed vertically upwards.
10 Radiation that proves the Big Bang theory
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The universe’s first stars Massive, short-lived stars formed 100 million years after the Big Bang in small protogalaxies. Providing immense heat and ionising surrounding gases, they would have provided the necessary bridge towards heavier elements, such as oxygen, nitrogen, carbon and iron. Called Population III stars, they would have formed from the hydrogen and helium prevalent in the early universe, and created other elements within themselves via nuclear fusion. Their deaths would have resulted in huge explosions, providing the necessary material for the next generation of stars. Scientists observed the galaxy CR7 in June 2015, and said its stars had every characteristic expected of Population III stars and formed in waves, just as predicted.
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Radio astronomers Arno Penzias and Robert Wilson accidentally discovered Cosmic Microwave Background (CMB) radiation in 1965 as they were scanning the sky using the Holmdel Horn Antenna in New Jersey. They were trying to find invisible light waves but background interference kept hampering their work, leading them to try all manner of ways to eliminate the issue. With the signal remaining, the pair threw up their hands and came to an astonishing conclusion: the interference was coming from somewhere outside of our galaxy. They passed the data to other astronomers and were startled to hear that it was most likely the last remnant of light from the Big Bang. The radiation had taken roughly 13.72 billion years to reach Earth, having originated 378,000 years after the Big Bang (the moment when photons could travel freely). The discovery of this almost-uniform background of radio waves has helped astronomers work out the composition of the universe and even led to the hypothesis of dark matter and dark energy. Today, CMB radiation is being mapped by the European Planck mission, which launched in 2009.
50 greatest discoveries of all time
8 Galileo discovers the moons around Jupiter In 1610 Galileo Galilei thought he had caught sight of three stars in a line close to Jupiter. That excited the Italian astronomer but it was only on closer observation that he noted something unusual. He expected Jupiter to leave the three stars behind as it moved. Instead, the stars moved to the west of the planet, were joined by a fourth and were carried along with the planet – he realised they were not stars but moons. It was believed that the Sun and the Moon orbited the
6
Earth, yet discovering four moons in motion around Jupiter showed there could be other centres of motion. Galileo’s observations flew in the face of the geocentric model of the Solar System and provided strong evidence that the Sun was at the centre of the universe rather than Earth. Galileo was charged with heresy but was, of course, later proved to be correct. His work helped to separate science from philosophy and religion.
9 We’re made of stardust Scientists have known for a while that the atoms in our bodies have their origins in stars born more than 4.5 billion years ago. Indeed, once it was realised that the universe began with just hydrogen and a small dose of helium, things fell into place. More than 96 per cent of the human body is made of hydrogen, oxygen, carbon and nitrogen. We also contain calcium, potassium, sulphur, magnesium, iron, zinc, copper and many other small elements. All except hydrogen originates from the early stars and that is because they are akin to nuclear reactors. Without the stars, we wouldn’t exist. For as the stars converted hydrogen to helium they produced the stuff that makes up our bodies. When those stars exploded in death, the elements reached Earth and provided the building blocks for life. So we can, in effect, count the stars as our ancestors.
Finding a way to throw spacecraft into orbit around planets
In 1957 the Soviet Union launched Sputnik 1 – the first artificial satellite sent into an elliptical low Earth orbit – and it not only sparked a Space Race with America (NASA was formed the following year), but it proved that humans had worked out how to throw a spacecraft into orbit around a planet. The Soviets followed up their impressive feat by sending spacecraft to the Moon. But it wasn’t until April 1966 that the Soviet Luna 10 spacecraft orbited Earth’s natural satellite – beating the US by four months. However, NASA’s Mariner 1 was the first spacecraft to orbit another planet, arriving at Mars in 1971. Mariner 1 won the race to Mars by a month. Without some complex calculations involving physics, orbits and gravitational pull, none of this would have been possible. Initial attempts relied on the work of Johannes Kepler who worked out that orbits were elliptical. But throwing spacecraft into orbit around planets has had another benefit: we can now use gravity assist to speed up craft, save fuel and better travel from one planet to another.
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The universe is 13.82 billion years old We would wish the universe a happy birthday if only we had a precise date to pin it down to. As it stands currently, we can only make very well-educated estimates based on the evidence we have before us, but scientists can now say with great certainty that it is 13.82 billion years old – 100-million-years older than it was previously imagined to be. The figure was arrived at in March 2013 when the European Space Agency’s Planck space telescope observed a billion points in the sky and produced a detailed map of the tiny temperature fluctuations in the Cosmic Microwave Background over the course of 15.5 months.
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50 GREATEST
DISCOVERIES OF ALL TIM E
4
There are galaxies beyond the Milky Way
3
The universe is expanding
5
Water on Mars
There have long been high hopes of discovering life on Mars but while we still await that particular breakthrough, the quest to find running water has yielded much better results. In June 2000, NASA imaging scientists using the Mars Global Surveyor (MGS) spacecraft observed features that pointed towards there being current sources of water at or near the Red Planet’s surface. The images appeared to show gullies formed by flowing water as well as deposits of soil and rocks transported by those flows. Since then, further evidence has been found. In 2006, analysis of pictures taken by MGS revealed deposits that suggested water carried sediment through them at some point during that decade. Scientists became very excited last September when dark streaks photographed on steep slopes by the Mars Reconnaissance Orbiter during the planet’s warm season were found. These streaks were formed by briny water flowing downhill, and are known as recurring slope lineae. Although flowing water has not been directly seen, it is the strongest evidence we have to date that Mars may not be as dry as it was once imagined to be, and that liquid water may still exist on the surface, albeit intermittently. It means the possibility of finding life on Mars has been heightened, but scientists eager to send Curiosity over for a closer inspection worry that the rover could be carrying microbes picked up from Earth. Discussions over the best way to proceed are continuing.
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With the discovery of other galaxies beyond the Milky Way, scientific perception of the universe had suddenly grown by somewhere in the region of a thousand million. Yet there was more to come from Edward Hubble. He published an important paper in 1929 that included the ground-breaking observation that the universe was expanding. Having looked at the light from distant galaxies, he wrote that they were not only moving in space but that the further away they were, the faster they were receding. Much has been written over whether Hubble can actually lay claim to this discovery. Hubble had drawn on data collected by the American astronomer Vesto
Slipher in 1912 and combined it with his own observations. But there is no doubt that the paper was a landmark in astronomy, and the principle behind the discovery became known as Hubble’s Law (which says relative velocity equals distance multiplied by Hubble’s constant). Since then, there have been other theories. Observations from the Hubble Space Telescope – named in honour of the astronomer’s contribution to human understanding of space – revealed the universe is not only expanding but is speeding up. Rather than gravity holding it back, dark energy is believed to be causing it to accelerate. We are yet to discover quite why and how.
There was a time when astronomers believed the Milky Way to be the extent of the universe. It was only when Edward Hubble proved in the 1920s that it was merely one of many galaxies that attitudes began to change. Fellow astronomer Harlow Shapley had calculated that the Milky Way was 300 light-years in diameter, but Hubble theorised that the observable spiral nebulae were much further away. His hunch was correct, changing the way we looked at the universe forever. Hubble spent several months using the Hooker telescope at California’s Mount Wilson Observatory to focus on Andromeda, which, at the time, was the largest known spiral nebula. He was looking for exploding stars and he found three, noticing one brightened and faded predictably over the course of 31.4 days. It came to be called V1 (Hubble variable number 1) and, crucially, Hubble’s subsequent measurements involving 36 variable stars in Andromeda found it was an eye-opening 900,000 light years away. Following this astonishing calculation (V1 was eventually reassessed as being 2.4 million light years away), it was posed that the Milky Way was certainly not alone and that V1 was in another galaxy. Hubble went on to discover more galaxies, and the vast nature of the universe soon became all too stark.
50 greatest discoveries of all time
2
The first alien world to be found
Italian Dominican friar, philosopher and astrologer Giordano Bruno proposed an infinite universe with stars surrounded by exoplanets and the potential for life away from Earth. Yet the first confirmation of an alien world outside of our Solar System was not found until 392 years had passed, following his death in 1600. The honour fell to both Polish astronomer Aleksander Wolszczan and Canadian astronomer Dale Frail, who discovered a planetary system around a pulsar (a class of neutron star) known as PSR B1257+12 in 1992. Despite being located 1,000 light years from Earth in the constellation of Virgo, they were able to use the pulsar timing method to detect two
planets in its orbit. Since pulsars rapidly rotate and send out a very regular and stable beam of intense electromagnetic radiation, any detection of a slight but regular variation points towards the existence of extrasolar planets. Two years later, a third planet was found in this system (a fourth, claimed in 1996, was retracted). Since then, more than 1,750 exoplanets have been discovered, including 52 Pegasi b, a gas giant which was the first to be found around a Sun-like star in 1995. Wolszczan was awarded the Beatrice M Tinsley Prize by the American Astronomical Society in 1996, while Frail was awarded a Guggenheim Fellowship in 2010.
Finding exoplanets Exoplanets orbit other stars in the universe and there are various ways to find them 1 Microlensing
2 Direct imaging
3 Astrometry
This relies on a star moving in front of one that is being observed. The light from the more distant star is bent around the closer one, causing a bright, large disc of light to appear, which indicates the presence of such a body to astronomers.
Direct imaging is a difficult way of finding exoplanets but not impossible: the first was discovered in 2004. As the name suggests, it’s literally taking a photo of what can be seen through a telescope using either visible light or infrared.
Using astrometry, it’s possible to measure the precise positions and movements of stars and exoplanets but it’s not entirely easy with tiny bodies. Gaia is 3D mapping a billion stars in the galaxy and it’s expected to discover many exoplanets.
4 Pulsar timing
5 Transit
6 Radial velocity
When exoplanets orbit a pulsar, they will cause irregularities in the timing of the pulsars. By measuring the timing of the pulses and watching out for such disturbances, it is possible to discover exoplanets and their orbits.
This method seeks evidence of a planet passing between the parent star and Earth. The slight dimming that this will cause as it blocks the light not only tells astronomers there is a possible exoplanet, it indicates the size of the body and the orbital period.
Known as Doppler spectroscopy, radial velocity works on the basis that as a planet orbits a star, the star will feel the effects of the gravitational pull and wobble slightly. This can be measured by looking for changes in the star’s light spectrum.
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50 GREATEST
DISCOVERIES OF ALL TIM E
1 Discovery of ripples in space-time Albert Einstein, predicted the existence of gravitational waves almost exactly 100 years ago as a result of his general theory of relativity. The German-born theoretical physicist had said any accelerating mass should produce ripples in the fabric of space-time that propagate at the speed of light, which essentially means that a change in gravity will spread as waves or ripples through space. But decades of searching for evidence had drawn a frustrating blank. Yet on 11 February 2016, it was announced that physicists at the Laser Interferometer GravitationalWave Observatory (LIGO) had sensed, for the very first time, a wave emanating from a fraction-of-a-second collision of two black holes located 1.3 billion light years away. The coming together of this pair of huge masses – one 36 times the mass of the Sun and the other 29 times our star’s mass – confirmed general relativity and opened up the possibilities for scientists to look at the universe in a whole new way. It was also the first time that a pair of colliding black holes had ever been seen. The gravitational waves – which, incidentally, can be caused by anything capable of affecting
their surroundings including the explosions of a star – were actually noted on 14 September 2015 using the LIGO detectors at Livingston, Louisiana, and Hanford, Washington. According to the scientists, a mass three times that of the Sun had been converted into gravitational waves and there was a peak power output some 50 times that of the whole visible universe. Despite that, the effects were very weak, which is why gravitational waves have been difficult to detect. For this reason, the LIGO interferometers could detect a disturbance on a par with a fraction of a proton’s width. From this, there is hope that the discovery will let scientists observe hidden regions of space, opening new windows to the universe. By allowing for observations of the dark side of the cosmos, it should now be possible to peer as far back as the beginning of time, some 13.82 billion years ago, and it should begin to tell us more about black holes. Indeed, this is only the start. Astronomers fully expect to see the building of new observatories capable of listening out for ripples as a whole new field of gravitational-wave astronomy opens up. We can expect a tsunami of fresh findings in the coming years.
“It should now be possible to peer back as far as the beginning of time some 13.82 billion years ago” 26
Albert Einstein first predicted the existence of gravitational waves nearly 100 years ago with his general theory of relativity
@ Tobias Roetsch; Adrian Mann; NASA; ESA; Science photo library, Alamy; Getty images; Hubble; JPLCaltech; ASI; USGS; Goddard Space Flight Center; CI Lab; CERN; MSSS; M.Postman(STScI); CLASH Team
50 greatest discoveries of all time
27
Exploration Missions to the planets, our cosmic back yard and beyond 30 Are we alone in the Solar System? Can our own neighbourhood provide the answer to the quest for alien life?
38 How we’ll find another Earth It may now be a matter of when, and not if, we find another planet like our own
46 Record-breaking astronauts Journeying into space is a feat in itself, but who has the biggest bragging rights?
52 10 years around Mars Celebrate the ten-year anniversary of NASA's MRO arriving at the Red Planet
“The first discovery of an exoplanet heralded a revolution for astronomy”
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Record-breaking astronauts 28
30
Are we alone?
38
Finding another Earth
52
©NASA, Tobias Roetsch
Ten years on Mars 29
Exploration
30
31
Exploration
Potentially habitable worlds in the Solar System Mars
Europa
Ganymede
Callisto
So much has been said about Mars’ potential habitability. As the fourth planet from the Sun, it sits at the edge of the habitable zone where conditions are almost right for liquid water to exist. Recent evidence has shown there were once vast bodies of water on the surface billions of years ago, and there are still dribbles of water today. But we still don’t know if it did, or still does, host life.
Jupiter’s moon Europa is one of the icy satellites believed to have a vast ocean beneath its frozen crust that extends several miles deep. Here, life would be protected from solar radiation, while Europa’s eccentric orbit around Jupiter pushes and pulls the core, providing a heat source on the seabed. Plumes from this ocean fire into space, and it is through these that we can send spacecraft to detect signs of life.
The largest moon in the Solar System, recent evidence suggests Ganymede hosts an underground saltwater ocean beneath its icy crust. Importantly, Ganymede is the only moon with its own magnetic field, as on Earth our magnetic field keeps us safe from harmful solar radiation. Could Ganymede provide similar protection from both the Sun and Jupiter for its own potential microscopic inhabitants?
Another moon of Jupiter’s that could host an underground ocean, Callisto is the furthest of Jupiter’s four large Galilean moons and it is subjected to the least amount of fatal radiation. Its surface appears to be ancient, with very little activity appearing to have taken place aside from asteroid and comet impacts, unlike Europa, whose surface lines indicate a constantly shifting crust from the water below.
As little as a few decades ago, the suggestion that some moons or planets in the Solar System once hosted life, or perhaps still do, would have been met with heavy scepticism. Now, thanks to various robotic explorers, we know differently; there are several potentially habitable worlds in our Solar System alone. But the biggest question still remains, could one of these locations host existing life? We are getting close to resolving that question, and the answer – one way or another – will define our place in the universe. Essentially, the search for life in the Solar System boils down to three waves of exploration. The first wave, which included missions like the Jupiterorbiting Galileo spacecraft and the Saturn-orbiting Cassini spacecraft, proved the existence of possible habitable worlds – most notably Europa, Enceladus, and Titan, in addition to others we now think were once habitable like Mars. The next wave of exploration is the one we are currently entering, with upcoming spacecraft including the ExoMars rover and the Europa Multiple-Flyby Mission (EM-FM) – are these worlds actually habitable and, if so, could we expect to find anything there? The final wave, which we could enter in a few decades, will be the most crucial of all – does life exist on other worlds in our Solar System? Before we get too carried away, it’s important to address one key issue. We know that on Earth, wherever the conditions are suitable, life exists as
single or multicellular organisms. From the frozen wastes of Antarctica to the bottom of the deepest oceans, life is abundant almost everywhere we look. It makes sense, therefore, that if we find other worlds with similar conditions, they too could host life. The only problem is, we don’t exactly know what we’re looking for. “It is surprisingly difficult to find evidence of life,” Curt Niebur, lead programme scientist for NASA’s New Frontiers Programme (including missions like Cassini and the EM-FM), tells All About Space. “We’re not expecting to find a tree or a fish. The signs are going to be much more subtle.” What Niebur means by this is that any life in the Solar System is expected to be microscopic in size. We are unlikely to find a fish swimming in the ocean of Europa, or a mouse running across the surface of Mars. The reason is that, while places like this have the ingredients for life – water, a food source and a source of energy – none of them appear to have enough of any one of the three to sustain the larger macroscopic life we see on Earth. If there is life in the Solar System, it will be tiny. And, there isn’t some magical instrument that can look at a sample from another world and say with certainty whether it contains microscopic life or not. When asked what we need to do to prove life exists on another world, Niebur responds: “We don’t know. There’s no single silver-bullet measurement you can look at and say there’s definitely life there.”
“ExoMars rover will drill past the cosmic radiation degradation zone to collect well preserved samples at depth” Dr Jorge Vago, ESA 32
But it’s not all doom and gloom. While there is no “life detector” instrument at the moment, we do know the basics in terms of what life should – or could – look like. “There may be some tricks available to future missions,” says Steve Vance, leader of the Habitability team at NASA’s Jet Propulsion Laboratory’s Icy Worlds Astrobiology group. “Life creates particular suites of organic compounds, with preferred numbers of carbon atoms in each molecule, for example, and with specific right-handed versus left-handed orientations of the molecules, so called chirality. Life also tends to use the lighter versions of carbon and other atoms that make up its molecules, because these lighter isotopes take less energy to move. By contrast, organic materials seen on meteorites or in petroleum on Earth have more uniform distributions of carbon number, isotopic composition, and chirality.” This is a more complicated way of saying that we know how to look for the signs of life and how these signs should behave. And so, with that in mind, this second wave of robotic explorers that will be taking place over the next few years will be looking for some of these biosignatures in order to at least point us in the right direction. One of the most exciting forthcoming missions is the European-led ExoMars rover, which is expected to launch in 2018 with the help of the Russian Federal Space Agency (Roscosmos). Among the suite of instruments to be included on the rover will be instruments to look for signs of past or present life on Mars, and it will also take the first ever drill to the surface of Mars. This will analyse a sample of material up to two metres (6.6 feet) beneath the surface, where there is expected to be liquid water. This, as we know, is a key ingredient for all forms of life as we know it.
Are we alone in the xxxxxxxxxxxxx Solar System?
Titan
Enceladus
By far Saturn’s largest moon, Titan is the only body in the Solar System other than Earth known to have liquids on its surface. Unlike Earth, however, this liquid is not made of water but is composed of liquid hydrocarbons, methane and ethane, forming seas and lakes across the surface. For life as we know it, it would be difficult to survive in this environment. But what about life as we don’t know it?
Like the icy moons of Jupiter, Enceladus, too, appears to have a vast ocean beneath its frozen surface. Similar to Europa, it is thought to have hydrothermal vents at the bottom of this ocean, with vast plumes of liquid spraying out from the poles of the moon through cracks in the surface. The Cassini spacecraft recently flew through these plumes and scientists are awaiting the results in earnest.
Jorge Vago, the European Space Agency’s ExoMars project scientist, is pictured here at the Planetary Utilisation Testbed
Triton
It’s not just Jupiter and Saturn that have so-called “ocean worlds”. Triton, the largest moon of Neptune, is thought to have a rocky core and between this and the surface there could be an ocean of water. Triton is also one of the few moons that is still geologically active. With no mission to Neptune planned any time soon, though, it will be a long time before we find out how habitable it really is.
Venus
A surprise candidate, Venus is a hot and inhospitable world with surface temperatures approaching 455°C (850°F). But billions of years ago Venus might have been more temperate before it went through a runaway greenhouse effect – and a region of its atmosphere 55 kilometres (34 miles) above the ground has the most Earth-like conditions of anywhere in the Solar System.
Do Europa’s plumes of water that shoot into space hint at life beneath the moon’s frozen crust?
The possibility of the Allan Hills 84001 meteorite containing fossilised life sparked huge controversy
Streaks on Mars point to water existing on the surface today
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“ExoMars 2018 is going after molecular signatures of past life from very early in the planet’s history, around 4.4 to 3.8 billion years ago,” Jorge Vago, the ESA’s ExoMars project scientist, tells All About Space. “The rover will drill past the cosmic radiation degradation zone to collect well preserved samples at depth. It has a maximum penetration of two metres (6.6 feet) – a big deal since the deepest we have gone so far is less than ten centimetres (four inches).” Vago continues, “We need to target an ancient site known to have harboured lots of slow circulating water for prolonged periods. Fortunately we know of such places and we have recently selected one for the 2018 launch opportunity: Oxia Planum, in the Chryse Planitia region. The rover is also equipped with next-generation instruments for mineralogy and organics detection. It will be an amazing mission, full of interesting firsts.” A lot of firsts indeed, but not first for everything. There has actually been a search for life on Mars before: The Viking landers in the 1970s. They both conducted biological experiments to search for signs of life, with mixed results – amid a number of limitations on the instruments. “Our knowledge of astrobiology, life on Earth, has advanced considerably since then,” says Niebur. “Viking didn’t jump the gun, it did the best it could do with the state of science at the time. But we’ve learned a lot more since then.” And it is with that additional knowledge that missions like ExoMars will perform a more advanced search for life. One particularly intriguing instrument on board will be the Raman Laser Spectrometer, which will use a process known as Raman spectroscopy on another world for the first time. This can provide information about molecular vibrations, which can be used to identify molecules in a given sample or location – and possibly hint at the existence of life. “This has proven itself to be a very versatile and sensitive technique on Earth,” says Lewis Dartnell from the Space Research Centre at the University of Leicester, who is also working on the Raman Laser Spectrometer on the ExoMars rover. “It can be used to detect explosives or art forgeries, for example, and is able to detect hardy microbial life surviving in Mars-like environments on Earth, such as the Atacama Desert in Chile.” This isn’t quite the highly sought after “life detector” instrument we mentioned earlier, but its pretty close. If ExoMars can find life-like molecules on Mars similar to ones on Earth, why shouldn’t we think Mars is – or was – habitable? It may be that there is existing life on Mars or there could be fossilised microbial life hidden in the rocks. In fact, such an event sparked a worldwide media storm back in the 1990s. In 1996, scientists announced that a meteorite called Allan Hills 84001 contained evidence for microscopic fossils. Such was the intense speculation at the time that President Bill Clinton made a televised statement on the prospect of alien life being found. “Today, rock 84001 speaks to us across all those billions of years and millions of miles,” says President Clinton. “It speaks of the possibility of life. If this discovery is confirmed, it will surely be one of the most stunning insights into our universe that science has ever uncovered. Its implications are as far-reaching and awe-inspiring
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Heat shield The heat shield bears the brunt of atmospheric entry, slowing the spacecraft to a speed of 1,650km/h (1,025mph) at 11km (6.8mi) high before it is jettisoned at 7km (4.3mi).
Parachute The parachute is deployed and slows the main body of the spacecraft, while radar is used to track the position on the Martian surface.
Hunting for life on Mars How this European-led mission will search for signs of life on the Red Planet ExoMars is set to be the first European-led rover to land on the surface of Mars. Its launch on a Russian rocket is scheduled for 2018 and, despite concerns that this might slip back, this would allow for a Mars landing in 2019 with the help of a Russian-built lander. Compared to NASA’s Curiosity rover, it weighs about 600 kilograms (1,320 pounds) less at 310 kilograms (680 pounds), and it will rely on solar power while Curiosity has a nuclear power source – plutonium-238. The biggest difference, though, is their goals. While Curiosity was sent to ascertain the habitability of Mars in the past and present, ExoMars will be directly searching for the possibility of life on the Red Planet today.
The suite of instruments on board ExoMars includes a drill, which will obtain samples up to two metres (6.6 feet) below the ground, where liquid water could be abundant. Other instruments will look for biosignatures of life, and even attempt to find microbes that are life-like. The rover is to be preceded by the Trace Gas Orbiter (TGO), launching in March 2016, which will serve as its communications link with Earth. The TGO will also carry a demonstration lander called Schiaparelli, to test the technology – a parachute and thrusters – that will enable the rover to land on the Red Planet at a preferred site called Oxia Planum two years later, which is thought to be rich in clays shaped by water.
Solar power Camera
The solar panels on the autonomous ExoMars rover will produce 1,200 Watt-hours of energy, while a battery will store the solar energy collected by the panels.
On the top of the rover is a panoramic camera, which will take images of the surrounding clay-rich locale on the Red Planet.
Raman Laser Spectrometer This instrument will perform the first Ramon spectroscopy on another world, which will study the vibrations of molecules to determine their characteristics.
Drill The rover will drill further underground than any Martian mission before it, collecting samples up to a depth of 2m (6.6ft).
Wheels With its six wheels, the rover will be capable of travelling up to 100m (330ft) per day with a preprogrammed destination sent by ground control.
Are we alone in the Solar System? Operations
FREND
The Trace Gas Orbiter will arrive at Mars in 2017 and will study the Martian atmosphere for at least one Martian year (687 Earth days). It will also serve as a relay satellite for the ExoMars rover.
The Fine Resolution Epithermal Neutron Detector (FREND) will map hydrogen on the surface up to one metre (3.3 feet) deep, helping locate water-ice underground.
CaSSIS The Colour and Stereo Surface Imaging System (CaSSIS) will, as its name suggests, take images of the Martian surface at a resolution of five metres (16 feet) per pixel.
NOMAD The Nadir and Occultation for Mars Discovery (NOMAD) instrument will measure the amount of methane in the Martian atmosphere.
ACS The Atmospheric Chemistry Suite (ACS) will study the chemistry of the Martian atmosphere, and also investigate its structure.
Airbag Propulsion The parachute and rear heat shield are jettisoned at 1.3km (0.8mi) above the ground, when a liquid propulsion system kicks in.
The ExoMars rover features a crushable structure for a safe landing. This will act like an airbag and crush on impact in order to cushion the blow for the spacecraft.
Landing
Ramps
The liquid propulsion system will slow the spacecraft to less than 2km/h (1.2mph) at a height of 2m (6.6ft). The vehicle then drops to the ground, with its crushable structure absorbing the impact.
Once the craft has landed safely, the surface platform lander will unfold and deploy the ramps. This will create an octagonal shape, allowing the rover to drive onto the surface of Mars and begin its exploration.
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Searching for life
Inactive Active Future
Viking 1 and 2
Curiosity
ExoMars rover
Mars 2020 rover
Cassini-Huygens
Enceladus Life Finder
Launched: 1975 Destination: Mars Notable findings: Controversial signs of life on Mars
Launched: 2011 Destination: Mars Notable findings: Past habitability of Mars
Launch date: 2018 Destination: Mars Mission objectives: Search for life on Mars
Launch date: 2020 Destination: Mars Mission objectives: Investigate past/ present life on Mars
Launched: 1997 Destination: Saturn Notable findings: Bodies of liquid on Titan, plumes on Enceladus
Launch date: TBC Destination: Enceladus Mission objectives: Investigate the habitability of Enceladus
Venera probes
Galileo
Launched: 1961-1984 Destination: Venus Notable findings: Earthlike conditions on Venus
Launched: 1989 Destination: Jupiter Notable findings: Icy moons of Jupiter
Jupiter Icy Moons Explorer (JUICE)
Europa MultipleFlyby Mission
Launch date: 2022 Destination: Jupiter Mission objectives: Investigate Ganymede, Callisto and Europa
Launch date: 2020s Destination: Europa Mission objectives: Investigate the habitability of Europa
Rosetta
Voyager 2
Launched: 2004 Destination: Comet 67P/ Churyumov-Gerasimenko Notable findings: Organic molecules on a comet
Launched: 1977 Destination: Outer Solar System Notable findings: Triton, icy moon of Neptune
Are we alone in the Solar System?
as can be imagined. Even as it promises answers to some of our oldest questions, it poses others even more fundamental.” Teams of scientists subsequently tore apart the research, however, and by the turn of the century the initial hypothesis was deemed extremely unlikely. This highlights just how difficult it is to find or disprove life – but it also highlights the intense desire around the world for this ultimate question to finally be answered. “Who will believe you when you claim to have detected signs of life? The answer is, not many people,” explains Vago. “We can realistically aspire to perhaps making a possible detection of past life, but confirmation will likely require bringing samples back to Earth for analysis.” It is not just ExoMars that is of interest, though. As mentioned, at least two other worlds in the Solar System – Jupiter’s moon Europa and Saturn’s Enceladus – are believed to have vast oceans of water beneath their icy surfaces. Recently, NASA’s Cassini spacecraft flew through a plume of ejected material from the subsurface ocean of Enceladus to make a primitive analysis, but the results of that flyby are still being analysed. But, in the next
decade, new missions will launch that will ascertain the habitability of worlds like this in detail. Of great interest is the Europa Multiple-Flyby Mission (EMFM), which will receive a more formal name like Cassini nearer its planned launch date in the 2020s. This spacecraft will perform 45 flybys of Europa, conducting a detailed study of the moon and its surface. There is a possibility that the spacecraft will include a lander to touch down on the ground, and while this is unlikely to directly sample the ocean underneath, it could provide an unprecedented glimpse at another habitable world like Earth. There is one big red flag we haven’t addressed yet, though: planetary protection rules. The issue is that, if worlds like Europa and Mars are so conducive to life, then accidentally transporting Earth-based life forms there on a spacecraft would likely allow them to thrive, and might mean that a future detection of life is not alien – but merely a traveller from our own world. “I do not want to spend 20 years getting a mission to the ocean of Enceladus or Europa off the ground, and get there to discover Earth life from us,” says Niebur. “I could do that just by walking out of my back door.” Under guidelines drawn up by the Committee on Space Research (COSPAR), any
“If life arose independently twice in just one Solar System, it would suggest there could be life everywhere” Dr Curt Niebur, NASA
locations that could potentially host life – such as regions on Mars with liquid water – are deemed to be “special regions”, where a lander can only go if it meets extremely strict sterilisation rules. These regions would be off limits to humans, owing to the huge amount of microbes and bacteria we carry, unless the rules are changed. There are obviously good reasons and intentions for these rules. Some have bemoaned them, but they highlight how, in our continuing search for life, we must be careful not to get carried away and accidentally contaminate an area that would otherwise be of huge interest. Perhaps the greatest question of all, though, is why? What makes the search for life in the Solar System so important? If we find a handful of tiny microbes underneath the frozen surface of Europa, does that really mean anything important? Yes. Yes it does. The implications of at least one other world independently developing life in the Solar System would be huge. “If the conditions for life exist beyond Earth but life did not arise there, it suggests that life is extraordinarily precious in our universe,” says Niebur. “But if life arose independently twice in just one solar system, to me, that would suggest that based on there being trillions of trillions of solar systems in our universe, there could be life everywhere.” Whether there is life or not remains one of the great questions of human history. But we are now closer than ever to finding out – and the results from upcoming missions like ExoMars and the EM-FM will pave the way to an answer, one way or the other. Rosetta flight director, Andrea Accomazzo (left), receiving confirmation that Philae successfully landed on Comet 67P
The Cassini spacecraft has taught us much about Saturn’s moons to date
@ Adrian Mann; ESA; NASA; JPL-Caltech
Curiosity continues to find evidence that Mars was once habitable, or still is today
The ExoMars EDM Structural Model is lowered onto the multishaker for vibration testing
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38
EARTH It may now be a matter of when, and not if, we find another planet like our own
The first discovery of an exoplanet heralded a revolution for astronomy, eventually revealing just how many such objects could exist in the galaxy. It turns out that they are a legion. Now a second, more exciting revolution is taking place in exoplanetary science: the search for habitable, Earth-like worlds. When the first exoplanets – planets in other star systems – were being found from 1989 onwards, they were initially gas giants like Jupiter, and quite often much larger. Exoplanet detection was very much in its infancy throughout the 1990s due to the technological limitations of the time, so it made sense that large gas giants – and even larger
‘brown dwarf objects’ – would be the first targets to be spotted. Those orbiting very close to their parent stars also generated strong and rapid signals for the transit and radial velocity search methods, which were responsible for the majority of exoplanet discoveries. Although this was a major development for planetary science, astronomers still had to use their ingenuity to actually find these worlds. Even that first exoplanet from 1989 (Gamma Cephei Ab) couldn’t be officially confirmed as a planet until 2002. And none of the discoveries seemed to answer the most obvious and tantalising question: are there life-bearing worlds like Earth out there too?
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xxxxxxxxxxxxx Exploration
Top six most Earth-like worlds To date, we’ve found several candidates that could be similar to our home planet
Earth
Size: 6,371km (3,959mi) Mass: 5.97x1024kg (1.317x1025lb) Parent star: G-type
An artist’s impression of Exoplanet hunter, CoRoT
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Kepler-438b
Size: 1.12 times Earth Mass: Unknown Distance: 470 light years away Parent star: Red dwarf Discovered by: Kepler Space Telescope (2015)
Kepler-442b
Size: 1.34 times Earth Mass: 2.3 times Earth Distance: 1,120 light years away Parent star: Orange dwarf Discovered by: Kepler Space Telescope (2015)
Gliese 667 Cc
Size: 1.54 times Earth Mass: 3.8 times Earth Distance: 23.62 light years away Parent star: Red dwarf binary system Discovered by: European Southern Observatory (2009)
Since those pioneering days, astronomers have developed a toolkit of exoplanet search techniques to help them answer this very question. They’ve been helped in no small way by the development of rapidly deforming mirrors that counteract Earth’s turbulent atmosphere and increase the resolving power of ground-based telescopes (adaptive optics), ever-more powerful computer systems and better search algorithms. But discovery of the most exoplanets has so far been bagged by dedicated space-based missions such as the European Space Agency’s (ESA's) Convection Rotation and planetary Transits (CoRoT) and NASA’s Kepler Space Telescope, launched in 2006 and 2009 respectively. At the time of writing there are 1,995 confirmed exoplanets, with thousands more possible candidates awaiting confirmation. And Kepler alone has discovered the large majority of these using the transit method. That is, Kepler observes changes in brightness as planets cross in front of their host stars – provided their orbital orientations allow that from the spacecraft’s vantage point. Kepler’s main aim was to try and spot Earth-like planets orbiting Sun-like stars, especially in those stars’ habitable zone (HZ), which is the orbital region within which a planet could support liquid water – an essential requirement for life. Too far away from the star and any planetary water could freeze, and too close and it could boil away. The HZ is also known as the ‘Goldilocks Zone’, as it is not too hot, not too cold, but just right. So of all the exoplanets found so far, are any of them small and rocky like Earth? According to NASA Jet Propulsion Laboratory’s New Worlds Atlas, the total number of terrestrial, Earth-like planets among the 1,995 found currently stands at 93. The largest of
How we’ll find xxxxxxxxxxxxx another Earth
KOI-3010.01
Size: 1.58 times Earth Mass: Unknown Distance: 1,250 light years away Parent star: G-type Discovered by: Kepler Space Telescope (unconfirmed)
Kepler-62e
Size: 1.61 times Earth Mass: 4.17 times Earth Distance: 1,200 light years away Parent star: G-type Discovered by: Kepler Space Telescope (2013)
Kepler-452b
Size: 1.63 times Earth Mass: 5 times Earth Distance: 1,400 light years away Parent star: G-type Discovered by: Kepler Space Telescope (2015)
“Detecting a rocky object at the right distance from its star is the necessary first step but then it has to be followed up by atmospheric detections” Professor Heike Rauer, German Aerospace Centre these, GJ 581e, has just over three times the mass of Earth, while the smallest, PSR B1257+12, has a mass 1.6 times that of our Moon. Do any of these worlds reside within their stars’ habitable zones? Yes. In fact, 24 such worlds have been confirmed since 2011, with a further 24 candidates awaiting confirmation since 2007. The majority of these discoveries also come from Kepler, which has already doubled its original 3.5-year mission life. Using Kepler’s data in 2013, Erik Petigura, a graduate student at the University of California, Berkeley, conducted an analysis of the likely number of habitable planets orbiting just the Sun-like stars in our galaxy. The estimate came to an astounding 11 billion! But there’s a complication. A terrestrial planet residing within a star’s habitable zone is still no guarantee of life – or even the presence of liquid water. A planet’s atmosphere will play a huge – if not a determining – role in its habitability. In our own Solar System we can see that both Venus and Mars (which are either very close to, or within, our Sun’s HZ) are very different places to Earth. Venus has an atmosphere composed almost entirely of carbon dioxide with 93 times Earth’s atmospheric pressure. The prevalence of so much
CO2 (a greenhouse gas) in Venus’ atmosphere makes it the hottest planet in our Solar System, with a surface temperature of 467 degrees Celsius (873 degrees Fahrenheit). Compare that to the closest planet to the Sun, Mercury (54 per cent closer on average than Venus), whose night-side temperature can drop to -173 degrees Celsius (-279 degrees Fahrenheit) simply due to its lack of atmosphere. Although Mars’ atmosphere is also composed of CO2 (95.97 per cent), the pressure is six per cent that of Earth’s at sea-level and the temperature can swing from -143 to 35 degrees Celsius (-225 to 95 degrees Fahrenheit). Although probes and landers show strong evidence that Mars may have once had flowing water in its ancient past, it is now effectively a cold, desert planet. Why then does Earth have a biosphere while its two closest planetary neighbours do not? The study of terrestrial worlds should help to solve mysteries like this. But that’s if we can find them. Professor Debra Fischer is in charge of the 100 Earths Project at Yale University. The aim of this pioneering enterprise is to find up to 100 habitable worlds in the stellar neighbourhood using ground-based instruments. But detecting Earth-like worlds is difficult. The
Professor Heike Rauer of the German Aerospace Centre is the principal investigator of the instruments onboard the ESA’S planet hunting mission, PLATO
NASA’s Transiting Exoplanet Survey Satellite (TESS) should scan the entire sky for possible Earth-like planets when it launches next year
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Exploration
solution the team has come up with is the EXtreme PREcision Spectrometer (EXPRES), combined with new data analysis techniques developed at Yale. This instrument will utilise the radial velocity detection method, where scientists look for periodic wobbles in stars’ spectra as they are gravitationally ‘tugged’ by orbiting planets. From that they should be able to determine orbital periods and mass ranges. Although spectrometers are ubiquitous in astronomy and the radial velocity method is a well-established planethunting technique, EXPRES is the first instrument of its kind. “One of the instruments’ strengths is that it’s very high resolution. The combination of resolution, stability, and bandwidth are new,” says Fischer. The team have even designed a vacuum enclosure for EXPRES to sit inside, which will stabilise the spectrum as far as possible to make looking for periodic wobbles easier. This is necessary as EXPRES will be looking for stellar radial velocities of just ten centimetres (four inches) per second, while the current state-of-the-art is one metre (3.3 feet) per second. Once completed, EXPRES will be installed on the Lowell Observatory’s 4.3-metre (14.1-foot) Discovery Channel Telescope. “This will focus on nearby stars, probably closer than 65 light years. And around those stars we hope to get out to the habitable zone for rocky planets between one and four Earth masses in size,” Fischer says. But it’s not simply the size of Earth-like worlds compared to their host stars that makes them difficult to find; it’s also their relative brightness. A terrestrial planet can be up to 250 million times fainter than its host star – often compared to trying to spot a candle flame in front of a lighthouse beam, but far more extreme. This is why it’s easier to try and spot such worlds indirectly, as is the case with transit and radial velocity spectroscopy, by seeing how they affect their stars’ light. However, Fischer and her team won’t be the only ones looking for exoplanetary Earth-analogs. Another team, led by Dr Daniel Batcheldor of the Florida Institute of Technology, is trying a more direct approach. A study led by Batcheldor has demonstrated that a Charge Injection Device (CID) can detect objects up to 70 million times fainter than a star in the same field of view. Charge Injection Devices have been around for a while, so why haven’t they been used for exoplanet searches before? “CIDs have historically been noisy, which means they’re not that sensitive. However, advances in manufacturing have allowed amplifiers to be introduced on each pixel, which reduce the noise and get similar results to Charge-Coupled Devices,” explains Batcheldor. Charge-Coupled Devices (CCDs) are well established as astronomical detectors and are also found in professional DSLR cameras. Although they have similar-sounding names, CIDs work differently from CCDs and have an advantage for this kind of work. Unlike on a CCD, each CID pixel can be addressed individually, allowing the brightest ones to be ignored. That way the pixels of interest, trained on the faint object, can continue collecting light. Batcheldor’s team tried out their CID on Sirius A, which with an apparent magnitude of -1.47, is the brightest star in the Northern Hemisphere. Sirius A has a white dwarf companion, Sirius B, which is
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Hubble vs. Scheduled for launch in 2018, the James Webb Space Telescope will show us Earth-like worlds like never before Secondary mirror The mirror brings the light from the primary mirror to a focus in the instruments behind the primary mirror.
Packed with instruments Solar array Hubble has two panels that absorb sunlight and convert it directly into electricity.
The aft shroud contains Hubble’s wide-field camera, a high-speed photometer, faint-object spectrograph, faint-object camera, highresolution spectrograph and fine-guidance sensors.
Primary mirror Measuring 2.4m (7.8ft) in diameter, Hubble’s mirror is the smoothest of its size.
The deployment of the Hubble Space Telescope in 1990
How we’ll find another Earth
James Webb Science Instrument Module (ISIM)
Gold segmented primary mirror 18 hexagonal segments made of metal beryllium and coated with gold are used to capture faint infrared light.
Webb’s cameras and science instruments are housed in a module behind the primary mirror.
Trim flap This ensures that the spacecraft is stabilised.
Secondary mirror The mirror reflects light gathered from the primary mirror into the science instruments.
Solar power array The solar power array is always facing the Sun, allowing sunlight to be converted into electricity to power the observatory.
Multilayer sun shield Five layers shield the observatory from the light, radiation and heat from the Sun and Earth.
Massive mirror Each of the James Webb’s hexagonal-shaped mirror segments measures 1.3m (4.2ft) across – about the size of a coffee table. Together, the primary mirror folds out to a size of 6.5m (21.3ft) in diameter. The 18 hexagonal mirror segments of the JWST’s primary mirror are currently under construction
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much dimmer with a +8.44 apparent magnitude. Were they able to detect it? “We were making our initial observations from Florida (possibly the worst place in the world to try astronomy), so Sirius B was still lost in Sirius A’s glare,” says Batcheldor. However, they did detect another faint star. “Our detection (designated Star ‘6’) was far enough away from Sirius A in the sky not to be a problem.” They detected Star 6 with a confidence level of 99.87 per cent. Batcheldor would like to continue by using the CID at the one-metre (3.3-foot) Jacobus Kapteyn Telescope at La Palma – which he helped bring out of hibernation with funding from the National Science Foundation. Projects such as CoRoT, Kepler and 100 Earths couldn’t detect molecules such as
oxygen, nitrogen, water vapour – or even chlorophyll – in a terrestrial planet’s atmosphere. But could the CID approach be able to do so? “The detection of chemical elements like that is done using transit spectroscopy and the relative strength of those lines is not something that we’d need a CID for,” says Batcheldor. Both he and Fischer say the most likely way such molecules will be detected is with transit spectroscopy, using telescopes such as the James Webb Space Telescope (JWST) due to launch late in 2018. So it seems that to fully answer the question of whether a planet is habitable will require multiple ground and space-based approaches. Such projects will follow up CoRoT, Kepler and other targets, as well as discovering numerous new planets of their own.
“The study of terrestrial worlds should help to solve mysteries like why Earth has a biosphere while its two closest planetary neighbours do not”
The JWST has a mirror surface area of 25 square metres (269 square feet); more than five times that of Hubble’s 4.5 square metre (48.4 square foot) primary mirror. One of JWST’s main aims is to study the atmospheres of exoplanets. Unlike Hubble, however, which can observe in infrared and ultraviolet wavelengths as well as the visible range, JWST is primarily an infrared telescope. But how would that benefit exoplanet observations? Molecules such as methane or water in exoplanetary atmospheres are expected to display the highest number of spectral features in this wavelength region. With transit spectroscopy, the JWST would be able to analyse an exoplanet’s atmospheric chemistry as it passes in front of its star. Of course, the transit method would also detect the exoplanet’s existence in and of itself. Combining this spectroscopic data with radial velocities from groundbased instruments would reveal a detailed picture of each planet. The ultimate aim would be to find a habitable (or life-bearing) world. And JWST has one more tool to help astronomers in that regard. Two of its instruments, the Near Infrared Camera and the Mid-Infrared Instrument feature
Ground-based telescopes such as the JKT in La Palma will be as essential as spacebased missions in hunting down Earth-like planets
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How we’ll find another Earth
Signatures of an Earth-like world O
O
O
O
Oxygen
Carbon dioxide
Life as we know it requires oxygen to survive
Life forms on an Earth-like planet are likely to release this gas
O
O H
H
N
Nitrous oxide
Water
O O
N
Likely to be given off by bacteria that thrives on an Earth-like world
Liquid water indicates an ideal temperature for life (as we know it) to survive
H H
O
C
H
H
Ozone Ozone, which will protect delicate life from harmful space radiation, will give off a notable signature
Methane This odourless gas could point to the existence of life
“There are currently 93 terrestrial, Earthlike planets among the 1,995 exoplanets that have already been discovered” What advantages would PLATO’s multi-optic design have over missions such as Kepler and CoRoT? Rauer says, “Those missions have done a great job in putting forward exoplanet science. In addition to their great discoveries they’ve also raised new questions about exoplanets. We now know that planets can be very different from those in our Solar System and many different types of planets and planetary systems exist.” She adds that the ability to follow up such spacecraft detections with ground-based telescopes and also with the JWST rests on the host stars’ brightnesses: “PLATO’s multi-telescope design provides us with a large ‘dynamic range’: the ability to observe very bright stars at the same time as fainter ones.” That means one PLATO camera would be sufficient for a bright star, but for fainter ones the light from all the cameras could be combined for much more accurate results. Rauer says that this would make PLATO’s exoplanet targets much better suited to follow-up observations than those of Kepler or CoRoT. And those follow-up observations, combined with PLATO’s results, would reveal planetary radii and masses. “This will allow us to separate rocky, terrestrial planets from mini-gas
planets [i.e. the size of Neptune]. This is an important stage to identify the best targets for the next step,” says Rauer. Once a terrestrial planet is found in a star’s habitable zone, it would be a prime target for investigation, including atmospheric spectroscopy. Rauer continues, “Take the example of our Solar System. Earth is a rocky planet in our Sun’s habitable zone and it has developed life. Our Moon is a rocky object in the habitable zone but it has no life (as it has no atmosphere). Detecting a rocky object at the right distance from its star is the necessary first step, but it has to be followed up by atmospheric detections.” If you can’t wait eight years for PLATO to become operational then NASA’s Transiting Exoplanet Survey Satellite (TESS) is expected to launch in August 2017. Using the same transit detection technique, TESS will survey 200,000 of the bright stars across the entire night sky over a span of two years. It’s expected that TESS will find around 500 terrestrial planets during its search. Identifying a life-bearing world like Earth in our home galaxy would be the most monumental discovery in the entirety of human history. If these planets are out there, they can’t hide from us for much longer.
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@ Tobias Roetsch; NASA; JPL-Caltech; SETI Institute; Marshall Space Flight Center; Emmett Given; IAC; DanielLópez; ESO; L. Calçada; Tim Pyle; DLR; ESA; CNES; D. Ducros
coronagraphs that could block stars’ light and enable direct imaging of their planets, like with Batcheldor’s CID method (and he himself would like to see a future space-based mission with such a detector). Although the worlds would only look like small specks, scientists would still be able to use spectroscopy to tell the planets’ overall colour, the presence of weather systems, seasonal differences and even the existence of any vegetation. And JWST won’t be the only space telescope hunting for Earth-like worlds. The PLATO mission (PLAnetary Transits and Oscillations of stars) is part of ESA’s Cosmic Vision Programme and is expected to launch in 2024. The mission will monitor a million nearby stars for signs of exoplanets, and like Kepler and JWST, will use the transit method of detection. In order to observe so many stars in detail, PLATO will use 34 separate, small telescopes and cameras. This approach makes it different from CoRoT and Kepler, which are both telescopes with single instruments. Again, as with JWST, PLATO’s data will be combined with radial velocity measurements from ground-based observatories to build up a full picture. “The mission’s baseline observing scenario will cover six years of science operations. During this period we will observe two ‘long pointings’ that will last two to three years and a number of ‘short pointings’ lasting two to five months,” says Professor Heike Rauer of the German Aerospace Centre and principle investigator of PLATO’s instrument consortium. Altogether, PLATO will cover 50 per cent of the sky, with a near equal divide between hemispheres.
C
Journeying into space is a feat in itself but who has the greatest bragging rights? There appears to be a record for just about anything. From the longest fingernails and the fastest tortoise to the largest arcade machine and the wealthiest cat, they can range from the curious to the downright weird. Tens of thousands of people from virtually every country across the globe clamour for a place in the record books each year, but few are as out-of-this world as the feats that have taken place in space. In April this year, Guinness World Records confirmed that ESA astronaut Tim Peake had achieved the fastest marathon in orbit, having run the London Marathon 400 kilometres (249 miles) above Earth on the
First man on the Moon
An obvious one, for sure, but no less important for it. Neil Armstrong had viewers glued to their TV sets when he made his giant leap for mankind on 21 July 1969 and walked on the Moon for three hours.
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International Space Station (ISS) in a rapid three hours, 35 minutes and 21 seconds. In March 2015, it awarded two world records to a Japanese robot astronaut called Kirobo, who returned from the ISS having become the first robot to have a conversation in space and the first astronaut companion robot. In February 2015, 1,108 people enjoyed a recordbreaking astronomy lesson in Kalamunda, Australia, at the Maida Vale Nature Reserve to learn more about the night sky. And so it goes on. We look at some of the amazing records set and broken by the astronauts who have pushed the boundaries of human discovery.
Most time in space Gennady Padalka has spent 879 days in space over five missions. The cosmonaut is closely followed by Yuri Malenchenko who has spent 828 days away from Earth over six flights and, like Padalka, is still active.
First to record an original song in space Canadian astronaut Chris Hadfield took some time out while on the International Space Station to record a Christmas-themed song called Jewel In The Night on 23 December 2012, posting it on social media the next day.
Record-breaking astronauts
FIRST TO GO INTO SPACE
LONGEST OCCUPATION IN SPACE
Valeri Polyakov Russian cosmonaut Valeri Polyakov was no stranger to a lengthy stay in space. As a 46-year-old, he was on board Soyuz TM-6 on 29 August 1988 as it made its way to the Soviet Space Station Mir, where he spent 240 days before returning on 27 April 1989. But it was his second journey that proved so notable. Launching on Soyuz TM-18 on 8 January 1994, Polyakov was stationed on Mir for an incredible 437 days and 18 hours, only getting back to Earth on 22 March 1995. It is the longest occupation in space by just over 58 days. But then the Russians appear to be good at long stays. Sergei Avdeyev was in space for 379.6 days, while both Vladimir Titov and Musa Manarov embarked on a mission of exactly one
Yuri Gagarin became a national hero when he returned to the USSR following his time in space
Yuri Gagarin Space exploration was one of the many fronts of the Cold War between the US and the USSR. The Russians surprised America on 4 October 1957 by not only being the first to launch an artificial satellite, but the first to put a man-made object into orbit around Earth. It sparked a race to the Moon and to send a human far beyond our planet’s atmosphere. And it also led to the formation of NASA in 1958. But it was the Russians who made history again three years later. Soviet cosmonaut Yuri Gagarin became the first person to journey into outer space, setting off from Baikonur Cosmodrome on 12 April 1961 on board the Vostok craft, completing an orbit in one hour and 48 minutes. He reached a height of 327 kilometres (203 miles) before landing the same
day. And while there had been provisions for a ten-day stay for if an engine had failed, they were thankfully not needed. The round-trip meant the dream had become a reality and Gagarin was awarded the title of Hero of the Soviet Union by its leader, Nikita Khrushchev. The cosmonaut’s launch phrase ’Poyekhali’ (Russian for ‘Let’s go’) sparked the beginning of the US military scientists sent fruit flies to Space Age and an altitude of 108km (68mi) on board just three weeks a Nazi-designed V-2 rocket on 20 later on 5 May February 1947, parachuting their 1961, America was container back to the ground able to launch its and finding them to be first astronaut – Alan still alive. Shepard – into space.
First animal in space
year. In fact, of the top ten longest flights, only two astronauts are not Russian, with the longest American occupier in space being Scott Kelly who spent 340.4 days on the ISS between 27 March 2015 and 1 March 2016. Even then, he was accompanied on his year away from Earth by Russian Mikhail Korniyenko. While Polyakov was on Mir, he was kept busy with numerous experiments and scientific research and he orbited the Earth 7,000 times. When he returned, he insisted on standing up and walking when he left the Soyuz capsule, his aim being to show that humans would be capable of working on Mars after a long journey. He also said he could have gone on for another year if he had to.
Valeri Polyakov looks out of the window of the Mir space station as it completes a rendezvous operation with the Space Shuttle Discovery
ISS
BIGGEST SPACE GATHERING
STS-127
Koichi Wakata
Mark Polansky
Gennady Padalka
Douglas Hurley
As STS-127 docked with the ISS more than 354 kilometres (220 miles) above the Australian coast in July 2009, it led to the most extraordinary of meetups. What should have been a routine mission to deliver and install the last two components for the Japanese Experiment Module actually became
Michael Barratt
Christopher Cassidy
a record-breaker for the largest crowd to ever gather in orbit. The craft had seven astronauts on board while the ISS had six. So when the 13 people met, they were able to smash the previous record of ten. But as well as being large in number, the group was also diverse. That’s
Frank De Winne
Julie Payette
Roman Romanenko
Thomas Marshburn
because the Space Shuttle had six US astronauts on board – Mark Polansky, Douglas Hurley, Christopher Cassidy, Thomas Marshburn, David Wolf and Timothy Kopra – as well Canadian Julie Payette. But the ISS had Russian commander Gennady Padalka on board, who greeted the seven at the
Robert Thirsk
David Wolf
Timothy Kopra
ISS’s entrance as they floated in, with Michael Barratt from the US, Japanese Koichi Wakata, Frank De Winne from Belgium, Russian Roman Romanenko and Canada’s Robert Thirsk. While there have been other groups of 13 on board since, there have never been more.
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Exploration
Spacewalking by the numbers
Longest solo flight
707
This record is held by Russian cosmonaut Valery Bykovsky, who spent 118 hours, 56 minutes and 41 seconds alone on board Vostok 5 in June 1963. In that time, the craft completed 81 orbits of Earth.
14
Total number of spacewalks
Moon spacewalks
193
Spacewalks outside the ISS
11
Countries to fly spacewalkers
214 Total number of spacewalkers
128
1980
1985
US spacewalkers, more than any other country
A series of space firsts 1965
1970
1975
18 March 1965
3 June 1965
25 May 1973
7 February 1984
25 July 1984
7 December 1988
First ever spacewalk
America’s debut spacewalk
First repair job
First untethered spacewalk
First woman to perform EVA
First ever ISS spacewalk
NASA astronaut Bruce McCandless made the first untethered free flight using the jetpack-like Manned Manoeuvring Unit, also known as the MMU.
Svetlana Savitskaya became the first woman to perform an extravehicular activity (EVA) during the Soyuz T-12 mission to the Soviet space station Salyut 7.
Astronauts Jerry Ross and James Newman connected computer and electrical cables during the first ever spacewalk on the International Space Station.
Cosmonaut Alexey Leonov stepped outside Voskhod-2 for a 12-minute EVA but his bloated spacesuit stopped him re-entering the capsule until he dangerously reduced the pressure.
Ed White became the first American to conduct a spacewalk. He pushed himself out of the capsule using a hand-held manoeuvring oxygen-jet gun.
After the Skylab space station suffered some damage during its unmanned launch on 14 May 1973, the first of three repair crews were sent up to space in order to fix it.
Tallest astronaut: 1.93m (76in)
TALLEST PERSON TO GO TO SPACE
Jim Wetherbee When NASA was first seeking astronauts, it had a height cap of 1.80 metres (71 inches) due to the limited amount of cabin space that was available in the Mercury space capsule. But the requirements were soon relaxed, which was good news for Jim Wetherbee: at 1.93 metres (76 inches) in height, he became the tallest astronaut to ever fly in space. Wetherbee was selected to be an astronaut in 1984 and he piloted his first mission, STS-32, in 1990. He went on to become a veteran of six Space Shuttle missions, five of which he ended up commanding, which is a record for an American. One of the missions, STS-63, was the first joint flight of the Russian-American Space Programme, where he spent
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66 days, ten hours and 23 minutes in space. When his flight days were over, Wetherbee’s career hit new heights. He was appointed as deputy director of the Johnson Space Center in 1995, before becoming director of the Flight Crew Operations Directorate in 2000 and technical assistant to the director of JSC’s Safety and Mission Assurance Directorate in 2003. He retired in 2014. But what if you want to be an astronaut today? Well, to pass NASA’s long-duration flight physical, a nonpiloting astronaut needs vision correctable to 20/20, blood pressure below 140/90 in a sitting position and to be between 1.49 and 1.93 metres (58.5 and 76 inches) tall. Pilots, meanwhile, have to be between 1.57 and 1.91 metres (62 and 75 inches).
Early NASA height limit: 1.80m (71in) Tallest
Shortest
Jim Wetherbee
Richard Hieb Scott Parazynski Height:
Jon McBride Nancy Currie-Gregg Height:
Height: 1.93m (76in) Mission(s): STS-32, STS-52, STS-63, STS-86, STS-102, STS-113
1.91m (75in) Mission(s): STS-39, STS-49, STS-65
1.88m (74in) Mission(s): STS-5, STS-6, STS-7, STS-41-G
Height: 1.88m (74in) Mission(s): STS-66, STS-86, STS-95, STS100, STS-120
Height: 152cm (60in) Mission(s): STS-57, STS-70, STS-88, STS-109
Record-breaking astronauts
Spacewalk safety
MOST SPACEWALKS
Anatoly Solovyev It will surely take a long time before someone manages to break the record for the most spacewalks set by Russian cosmonaut Anatoly Solovyev. By the time he retired in 1999 – nine years after embarking on his first spacewalk – the former fighter pilot had a staggering 16 extra-vehicular activities (EVAs) under his belt. Solovyev’s first trip saw him spend seven hours and 16 minutes repairing thermal protection gear, and he went on to rack up a mighty 82 hours and 22 minutes worth of spacewalks. To put Solovyev’s achievement into context, NASA astronaut Michael
1990
Lopez-Alegria, who takes second place, carried out ‘just’ ten spacewalks during his career, totalling 67 hours and 40 minutes. Solovyez’s record was set during five missions on board the Mir space station and he could, if he had so wished, have embarked on a journey to the ISS, but he declined. It didn’t stop him from being name-checked in the 2013 blockbuster Hollywood movie Gravity, though. His impressive contribution to space also earned him many honours including Hero of the Soviet Union, an Order for Merit to the Fatherland and an Order of Lenin.
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Hazard Solution
During a spacewalk, there can be huge temperature fluctuations of close to 260 degrees Celsius (500 degrees Fahrenheit). Water-circulating tubing is placed within the spacesuit beneath layers of Mylar, which reflects sunlight. The suits also have cooling fans. The Sun’s glare is a major danger for astronauts due to the lack of a protective atmosphere in space. The body is covered by the suit and the helmet’s visor is coated with a thin layer of gold to filter out the Sun’s harmful rays. Making a mistake while performing a task because it hasn’t been encountered before could cause a mission to fail. The Neutral Buoyancy Laboratory near NASA’s Johnson Space Center has a pool with 6.2mn gallons of water: perfect for learning floating techniques. In the vacuum of space and the weightless environment, there is a lack of friction, which can result in an uncontrollable spin. A propulsive backpack called SAFER (Simplified Aid for EVA Rescue) has never been needed but it would push an astronaut back to base. The low pressure of space can cause nitrogen bubbles to form in an astronaut’s blood, which leads to the ‘bends’. After the cabin pressure is reduced, astronauts breathe pure oxygen within their suits for a few hours, which removes all nitrogen in their body.
2000
2005
2010
13 May 1992
December 1993
11 March 2001
22 April 2001
28 March 2005
15 January 2016
Three-astronaut spacewalk
First Hubble repair
Longest ISS spacewalk
First Canadian spacewalk
Preparing for ATV
First British EVA
STS-102 crew members Susan Helms and James Voss conducted a spacewalk that lasted eight hours and 56 minutes. It is the longest EVA to date.
Chris Hadfield installed the UHF antenna on the outside of the Destiny module on board the ISS and became the first Canadian astronaut to conduct a spacewalk.
Astronaut Leroy Chiao and cosmonaut Salizhan Sharipov installed navigational communications in preparation for the first Automated Transfer Vehicle (ATV).
When astronaut Tim Peake stepped outside the ISS’ Quest airlock, he became the first official British astronaut to carry out a spacewalk.
This unscheduled EVA involved three astronauts for the first time in order to help move the 4.5ton Intelsat VI satellite into Space Shuttle Endeavour’s cargo bay.
Two devices were fitted on the Hubble Space Telescope to fix its vision problems over five consecutive days of spacewalks. It was the first of five, with the last fix on 11 May 2009.
OLDEST PERSON TO GO TO SPACE
John Glenn As John Glenn travelled skywards on board the Space Shuttle Discovery on 29 October 1998, he made history and became the oldest person to go into space at 77 years of old. Over nine days, the shuttle orbited the Earth 134 times as part of mission STS-95. Glenn was a payload specialist and he was put through his paces in a series of science experiments to test how the lack of gravity and weightless environment would affect his body. It was something he had wanted to do for more than two years. Glenn was among NASA’s first astronauts, having been selected in 1959, and he was the first American to orbit the Earth when he flew the Friendship 7 mission in 1962. But in the late 1990s, he was still a sitting senator and he had been
lobbying NASA to allow him to fly so that scientists could conduct spacebased geriatric studies on him. Scientists used special sensors to record his brain waves and the movement of his eyes and chin over the course of four nights of the nineday mission. They measured the amount of oxygen in Glenn’s blood and recorded his movements day and night. His core body temperature was also measured and his levels of cognitive function, fatigue, alertness and mood were tested. Importantly, the researchers were able to compare the new data they had collected with the information gathered from Glenn’s previous visit to space, making his trip a particularly valuable one.
Youngest astronaut in space
Russian cosmonaut Gherman Titov was aged 25 years and 11 months when he went to space aboard Vostok 2 on 6 August 1961. He was the first to orbit the Earth multiple times – and the first to vomit in space! John Glenn was 77 years old when he was sent on a nine-day mission to test the effects of weightlessness on the body
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Exploration
LONGEST TIME IN LUNAR ORBIT
Ronald Evans While Ronald Evans was within the command module waiting for Apollo 17 to launch, he promptly fell asleep, much to the amusement of the crew. But there was plenty of time to be alert: the Apollo 17 mission lasted for 12 days, 13 hours, 51 minutes and 59 seconds and, of the crew who journeyed skyward on that dark December night in 1972, it was command module pilot Evans who ended up breaking the record for the longest time in lunar orbit. The mission marked Evans’ first time in space but, as it turned out, he would become the last person to orbit the Moon alone. He stayed in lunar orbit for six days and four hours, observing geological features and snapping pictures on board the command module, America. Meanwhile, fellow crew members Eugene Cernan and Harrison Schmitt landed and worked on the Moon. On his return flight to Earth, Evans completed a spacewalk of an hour and six minutes, exclaiming “hot diggety dog” as he took those first steps. During this time, his heart rate almost doubled to 140 beats per minute but he was able to take completed camera film from the outside of the spacecraft and examine the equipment bay area. He left the astronaut programme five years later in 1977. He died in his sleep of a heart attack in 1990, at the age of 56.
Ronald Evans carries out a spacewalk to retrieve film cassettes during Apollo 17
First animal in orbit
Soviet space dog Laika was launched into space on Sputnik 2 in 1957. Sadly, the former stray, who was found on the streets of Moscow, died within hours of the flight after becoming overheated, although Russia did not admit this until 2002.
LONGEST TIME ON THE LUNAR SURFACE
Eugene Cernan and Harrison Schmitt Eugene Cernan and Harrison Schmitt of the Apollo 17 mission were the last men to walk on the Moon but they sure made the most of their time up there. Having landed on 11 December 1972 following the first US manned launch in darkness, the pair spent 74 hours, 59 minutes and 40 seconds on the lunar surface using their time to complete three moonwalks, conduct scientific experiments and take a number of lunar samples. What’s more, in the process, Schmitt had become the first professional geologist to make a trip to the Earth’s natural satellite. It was also the most trouble-free of all the piloted missions.
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The crew landed at Taurus-Littrow, which increased their chance of acquiring highlands material and also allowed them better use of the Lunar Roving Vehicle (LRV). They stepped foot on the Moon just four hours later and their three EVAs ended up totalling 22 hours, three minutes and 57 seconds – the longest total number of moonwalks ever recorded. Meanwhile, the LRV ended up driving for four hours and 26 minutes. Of particular note is the fact that Cernan and Schmitt took the largest lunar sample to date – a whopping 108 kilograms (238 pounds) – making it a record-breaking trip all round!
Eugene Cernan drives the Lunar Roving Vehicle across the Moon’s surface at the Taurus-Littrow landing site
Record-breaking astronauts FASTEST HUMAN SPACEFLIGHT
Thomas P. Stafford, John W. Young and Eugene Cernan Apollo 10 was half a second late in taking off from its pad at 12.45.5pm on 18 May 1969 but it quickly made up for it on the overall mission. Crewed by Commander Thomas P. Stafford, command module pilot John W. Young and lunar module pilot Eugene Cernan, the spacecraft reached the blistering speed of 39,897 kilometres (24,791 miles) per hour on its return to Earth. That represented the highest speed ever attained by humans and, to put it into context, it was a mindblowing 32 times the speed of sound. The mission’s objective was to carry out the final rehearsal for the first manned lunar landing, the idea being that Apollo 10 would test the
rendezvous and docking operations between the Command/Service Module (CSM) and the Lunar Module (LM) – which the mission team had affectionately named Charlie Brown and Snoopy, respectively. Everything had initially gone well: Stafford and Cernan entered the LM when the craft reached the lunar orbit, leaving Young on the CSM and their pair’s craft got within 15.6 kilometres (8.6 miles) of the Moon’s surface. Yet there was a hair-raising moment when the LM was getting ready to head back to the CSM and started to spin wildly. Thankfully, it splashed down safe and well on 26 May following that superfast journey.
Most spaceflights Eugene Cernan (left), Thomas Stafford (centre) and John Young (right) of the Apollo 10 mission
The record for the most spaceflights is seven, with the honours shared between American astronaut Jerry Ross and Costa Rican-American Franklin Chang Díaz. Both have been inducted into the NASA Astronaut Hall of Fame.
Need for speed Apollo 10 travelled faster than the speed of sound 1,236km/h (768mph) SOUND
39,897km/h (24,791mph) APOLLO 10
62,140km/h (38,610mph)
Time it would take to travel from London to New York 4.5 hours
VOYAGER 1
7.8 min
173,800km/h (107,955mph)
5.4 min
GALILEO
1.9 min
265,000km/h (164,700mph) JUNO
1.3 min
Distance: 5,585km (3,470mi)
FURTHEST DISTANCE INTO SPACE
Longest mission duration by a woman
landing was impossible and attention turned towards getting the astronauts back home, the mission having been aborted. But there was a silver lining. Although it severely tested and re-wrote the emergency procedures of a mission on-the-fly, the astronauts were forced to circle the Moon, causing them to travel the furthest distance of any human to date. As they passed over the far side of the Moon at an altitude of 254 kilometres (154 miles) from the lunar surface, they were 400,171 kilometres (248,655 miles) away from Earth. They splashed down on 17 April 1970, 142 hours, 54 minutes and 47 seconds after take-off.
Jim Lovell, Jack Swigert and Fred Haise were presented with the Presidential Medal of Freedom and are pictured with President Richard Nixon
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© NASA; Getty Images; Bruce Weaver; Robert Markowitz; KSC
Jim Lovell, Jack Swigert and Fred Haise Apollo 13 was an unlucky mission. The idea had been for Jim Lovell, Jack Swigert and Fred Haise to land in the Fra Mauro area of the Moon. But one of the oxygen tanks on board the spacecraft suffered catastrophic failure, blowing up 55 hours and 55 minutes into its flight. It caused the other tank to fail, which in turn led to the Samantha Cristoforetti surpassed Sunita loss of the Command Module’s Williams’ record set in 2007 when she spent electricity, light and water. The 199 days, 16 hours and 42 minutes on alarming issue was relayed to the ISS. The Italian ESA astronaut mission control with the infamous set off on 23 November 2014 words, “Houston, we have a problem...” and returned on 11 June With the oxygen in the second 2015. tank fast depleting into space, a lunar
Exploration
A decade ago, NASA’s Mars Reconnaissance Orbiter (MRO) arrived at the Red Planet. All About Space celebrates its ten-year anniversary
Mission objectives Understand the present climate of Mars Work out the nature of the complex Martian terrain Search for evidence of aqueous and hydrothermal activity Identify landing sites for future Mars missions Return data from craft on the surface during relay phase
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10 years around Mars 10 March 2006
Arrival at Mars The MRO arrives in Martian orbit, initially entering a highly elliptical orbit over the planet’s poles. After initial checks, MRO begins an aerobraking manoeuvre that takes five months to complete, taking advantage of the natural brake provided by friction with the atmosphere to save thruster fuel. By the time the process is complete in early September, MRO’s 112-minute orbit around Mars ranges between 250 to 316 kilometres (155 to 196 miles) above the surface. The science operations are postponed until November to avoid a communications blackout.
13 December 2006
Targeting a layered canyon
Weather watch The Mars Color Imager (MARCI) delivers wideangle, lower-resolution images of the surface, allowing MRO to produce daily weather maps for the planet. In late 2007, MARCI captures a developing dust storm (red clouds) on the edge of the retreating north polar ice cap in Utopia Planitia. Northern-hemisphere storms tend to remain local (this one covers 500 kilometres (310 miles) and lasts 24 hours), but those in the southernhemisphere summer can envelope large swathes of the planet and last for weeks or even months.
2008
2007
2006
After months of aerobraking and instrument testing, one of the first targets for MRO’s High Resolution Imaging Science Experiment (HiRISE) camera is an area close to the Martian north pole. Here, frozen carbon dioxide (dry ice) is laid down by winter frosts, carrying with them dust from the atmosphere. As the upper layers of frost evaporate in spring, they leave dust behind, slowly building up a distinctive and complex layered terrain, whose inner structure is exposed around the edges of the canyons and craters.
7 November 2007
24 March 2006
19 February 2008
The first image
Capturing an avalanche
From an altitude of 2,489 kilometres (1,547 miles), the MRO takes its first image of the Martian surface, highlighting no smearing or blurring.
When MRO revisits the layered terrain at the north polar cap in the Martian spring, scientists hope to study the way in which carbon dioxide frosts evaporate from underlying sand dunes. It comes as something of a surprise, however, when an image from HiRISE ends up capturing no fewer than four separate avalanches thundering down a layered cliff face more than 700 metres (2,296 feet) tall. Further observations confirm that similar avalanches recur in Martian spring – they are probably triggered when blocks of dust-laden dry ice collapse as frozen carbon dioxide slowly thaws.
24 March 2007
MRO captures the Nili Fossae region This enhanced colour image, taken by the HiRISE camera in March 2007, shows an area of the Nili Fossae region. The image is part of a series of experiments to examine more than two dozen possible landing sites for NASA’s Curiosity rover.
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Exploration
27 May 2008
Flight of the Phoenix Throughout its decade of operation at Mars, the MRO has been used in conjunction with several other spacecraft, helping to identify potentially interesting landing sites for rovers, making observations to supplement those from other orbiters, and tracking other missions once they have reached the surface. In 2008, MRO uses its HiRISE to capture one such mission on its final descent to the Martian surface. The Phoenix Lander is shown here at an altitude of about 13 kilometres (eight miles), shortly after its parachute opens.
4 February 2009 Spiders from Mars One of MRO’s most spectacular discoveries are the curious, organic-looking patterns that develop in spring at the edge of the south polar cap. With a resemblance to trees or spiders, these dark patterns – also known as starbursts – form dark tendrils that spread out across the bright, frost-covered terrain. It is thought they are formed by sublimation – the direct transition of frozen carbon dioxide ice into gas. This happens in pockets beneath the surface and gas finds its way to weak points or fissures where it can break out, often carrying dust with it that falls back to the surface. This dust darkens the ice cap, so it absorbs more sunlight and heats up, which continues the cycle.
27 February 2008
2008
2009
MRO captures sand dunes defrosting
23 March 2008
Phobos flyby The MRO team turn the HiRISE camera away from Mars to image its two satellites, Phobos and Deimos, at the highest resolution yet obtained. The larger of the two moons, Phobos, orbits closer to Mars, circling the planet once every seven hours and 40 minutes. Seen in this image from 6,800 kilometres (4,200 miles), the potato-shaped moon’s most prominent feature is a crater called Stickney. The curious grooves that appear to radiate from the crater and run parallel with the moon’s longer axis are thought to be stress fractures, caused as Martian tidal forces push and pull on the satellite.
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15 October 2008
18 December 2008
MRO spots an unusual impact crater
Missing carbs
The MRO’s HiRISE camera captures a surprise crater on the surface of Mars. Its shape is noncircular, which is quite unusual for an impact crater. The crater also contains a bright patch of ice, despite being surrounded by terrain that has lost the majority of its ice cover.
Prior to MRO’s arrival, an important question for researchers was the nature of the water that had clearly run on the planet’s surface in its past. On Earth, water action on rocks converts them into carbonate minerals such as chalk and limestone through weathering, but acidic water tends to dissolve carbonates. The apparent lack of carbonates on Mars has led some to suspect that its ancient waters were acid and hostile to life. In 2008, however, MRO’s mineral imager CRISM finally discovers the first signs of carbonates exposed at the surface (appearing green in this image of the Nili Fossae canyon system).
10 years around Mars
21 February 2009
Martian Moon Deimos in high resolution The smaller of Mars’ moons, Deimos, is captured by the HiRISE camera onboard the MRO in February 2009. The moon is around 12 kilometres (7.5 miles) across and has a smooth surface, apart from dents created by the most recent impact craters.
14 July 2009
2010
Snapping Victoria Crater at Meridiani Planum
14 July 2009
2 March 2010
Crater Edge in Terra Sirenum
Low-latitude ice MRO’s Shallow Subsurface Radar Instrument (SHARAD) emits radar beams that penetrate the upper layers of the surface and send back reflections whose characteristics are altered by the electrical properties of the soil beneath. The presence of water makes the Martian sands electrically conductive and results in a particularly strong signal. In this image from 2010, yellow streaks represent individual radar tracks across the Deuteronilus Mensae region, and blue indicates the location of water ice detected by SHARAD. Deuteronilus Mensae is a region of collapsed canyonlands in the middle latitudes of the northern hemisphere – the ice seems to be buried below a thin layer of surface dust and rocks.
14 July 2009
View of Cape Verde from Cape St. Mary in midafternoon, in false colour
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Exploration
19 May 2010
Craters of ice The ‘Red Planet’ owes its nickname to the rusty Martian sands that cover its surface – but this HiRISE image in May 2010 reveals just how thin that surface layer really is. A small ten-metre (32.8foot) crater formed here after the area was last photographed in March 2008, and has pierced straight through the red soil to hit an underlying layer of ice, blasting snowy ‘ejecta’ across the surrounding terrain (colours have been processed to highlight the contrast). The crater is at mid-northern latitudes, where MRO observations suggest ice forms a major component of the soil.
13 September 2010 Martian glaciers
25 June 2010
Mars' wet north Ancient hydrated minerals had already been found in the southern highlands but the northern plains seemed to have a disappointingly dry history. Using the CRISM spectrometer, researchers target several craters and identify multiple signatures from hydrated, claylike minerals (such as those shown here at Lyot Crater). The crater seems to have punctured through the overlying dry soil to expose an ancient layer below, revealing evidence that watery and hospitable conditions were once global, perhaps 4 billion years ago.
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2011
2010
Shortly after MRO began imaging the surface, scientists began to notice features that were most likely created by glaciers – slow-moving rivers of ice that reshape the landscape as they move from higher altitudes to lower altitudes. In 2010, however, HiRISE captures a glacier that is still very present today – a flow of ice from an elevated mountain valley down to an eroded ‘snout’ on the level plain below. The surface of the glacier is covered in boulders up to three metres (9.8 feet) across that have been carved out of the valley walls. There are thought to be many more glaciers like it across Mars, often hidden beneath the red dust.
20 August 2010
4 August 2011
Mapping the atmosphere
Salt water flows?
MRO’s Mars Climate Sounder (MCS) studies the atmosphere by viewing sections through air above the horizon at a variety of wavelengths. This MCS image shows curtain-like profiles of the atmosphere above the northern hemisphere, based on 13 orbits’ worth of observations. Colour coding indicates different temperatures in the atmosphere ranging from -70 º C (-94ºF) in green, to a chilling -150 º C (-238ºF) in purple. MCS can also detect water ice clouds, accumulations of water vapour and dust storms.
Comparing images of a southernhemisphere crater called Newton across the Martian seasons, researchers find numerous dark trails forming and extending down the crater wall during spring and summer, before fading away with the onset of winter. These features, known as recurrent slope lineae, only form on the warmest, equatorfacing slopes, and the range of likely temperatures in these regions suggest they are most likely caused by salty water flowing just beneath the surface.
3 February 2011
Changing dunes The vast dune sea known as the Vastitas Borealis surrounds the Martian north pole just beneath the polar cap, and was long assumed to be in a state of permanent deep-freeze. However, this set of HiRISE images showing the area across two Martian years (roughly four Earth years) shows substantial erosion has taken place around the rim of a steep-edged dune. The changes are partially due to the seasonal accumulation and evaporation of carbon dioxide frost from the atmosphere, but are also affected by strong winds that shift the Martian sands and quickly wipe away signs of previous landslips.
10 years around Mars
6 September 2012
Tracking Curiosity Prior to the arrival of NASA’s Curiosity rover on Mars in 2012, MRO plays a key role in gathering data about its landing site in Gale Crater. As with Phoenix in 2008, the HiRISE camera tracks the probe during its descent, and it has been used to monitor the rover’s progress intermittently throughout the rest of Curiosity’s mission. The spacecraft’s rockets blow away the red surface dust during the “sky crane” descent stage to the Martian surface, revealing the darker iron-rich rock beneath, which can be seen in the centre of the photograph.
Mars Earth
16 July 2013
A coastal delta?
1 April 2012
2012
2013
Martian dunes covered in frost
Scientists have long speculated that the northern plains were once covered in a shallow ocean. In 2013, using HiRISE images of the Aeolis Dorsa region (which sits between the northern and southern hemisphere), researchers create an elevation map and find a series of inverted ridges fanning out as they run downhill – a structure similar to how river deltas flow into Earth’s seas. It’s the strongest evidence yet that the ocean theory is correct.
16 February 2012
Twister on the move The existence of dust devils on the Martian surface had been suspected since the 1970s, but MRO surprises everyone by delivering stunning images of these tornado-like whirlwinds in action. This relatively small-scale dust devil is about 30-metres (98-foot) wide and 800-metres (2,624-foot) high – others can grow much larger. Dust devils scour the Martian surface clear of dust, frequently leaving scribble-like dark trails where they expose the underlying bedrock. They are thought to form in the same way as Earth’s dust devils, when a pocket of warm air is trapped at the surface by overlying cold air and is then finally allowed to rise, creating a spinning updraft.
11 September 2012
Winter wonderland During the southern-hemisphere winter of 2006 to 2007, the MRO uses its Mars Climate Sounder to study cloud formations over the south polar ice cap. In 2012, a team of scientists announce a new analysis of this data, confirming the presence of a huge carbon dioxide snow cloud, some 500 kilometres (310 miles) across, hovering over the south pole. The cloud, made of frozen “dry ice” crystals, would deposit snow on the ground in the right conditions, perhaps explaining how the south pole grows from a small residual ice cap that persists through summer, to an extensive snowcap covering a large amount of the southern hemisphere.
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Exploration
16 January 2015
The spacecraft locates the Beagle 2 lander Beagle 2, a lander released by the Mars Express Orbiter on Christmas Day in 2003, is uncovered by MRO with its solar arrays partially deployed on the surface of Mars.
8 November 2013
Dunes on the rim of an impact basin
26 February 2014
Icy revelations MRO’s high-resolution cameras have discovered many unsuspected features on Mars, including unusual terraced craters like this one. At first glance, its bulls eye structure makes it look as though a second meteorite has struck the exact centre of an earlier crater, but the reality is rather different. Terraced craters form when an impact penetrates through layers of material that have different strengths – in this case, a relatively weak sheet of ice just below the surface has been hollowed out to form the crater’s wide outer walls, while the much tougher rock beneath has only been excavated at the point of impact itself.
2015
2014
2013
This sand dune is known as a barchan, which forms when the wind blows in one direction for long periods of time, causing it to slowly creep across the surface of Mars. This particular dune is located on the western rim of the Hellas impact basin, in the southern hemisphere of the Red Planet.
19 November 2013
23 March 2015
Spotting a recent impact
The south polar caps of Mars
The MRO’s continuous watch over Mars gives us the ability to see the rate of changes to the planet’s surface. This goes not just for seasonal processes such as the cycle of the polar caps, or the eruption of dust storms, but also for external factors such as impact cratering. This spectacular crater, which is 30 metres (98 feet) across but surrounded by an extensive pattern of impact debris, or ‘ejecta’, formed after July 2010 and before May 2012, between two imaging passes of MRO’s Context Camera. This more detailed false-colour image from the HiRISE camera uses blue to show where reddish surface dust has been blasted away.
The orbiter captures Mars’ south polar cap during the summer of Mars Year 32. Although the cap manages to survive each warm summer season, it is constantly changing shape with the sublimation of carbon dioxide.
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19 October 2014
Watching a comet flyby In late 2014, space agencies take precautions with MRO and their other Mars orbiters as the recently discovered Comet Siding Spring makes an unusually close approach to the Red Planet. When the comet was first discovered, it was thought to be on a possible collision course with Mars – with the potential to create a new crater several kilometres or miles across. In the end, however, Siding Spring passes within 140,000 kilometres (86,992 miles) of Mars – about one-third of the distance from the Earth to the Moon.
10 years around Mars
8 June 2015
Glassy debris found When meteorites hit a planet, the shock waves heat and compress the surface, often fusing sandy grains together to create glass. Impact glass is common on Earth but is hard to detect on Mars as its spectral signature is indistinct. In 2015, researchers find a way to prove that glass is widespread around many meteorite craters, such as Alga, the glass shown here in green. Impact glass can preserve traces of organic chemistry on Earth, so could assist in the search for life on Mars.
2 September 2015 Mars' lost atmosphere
Using the HiRISE camera, the Mars Reconnaissance Orbiter snaps the region Acidalia Planitia, which is featured in the bestselling novel and movie, The Martian.
28 September 2015
Water at last! Following on from the discovery of ‘recurring slope lineae’ in 2011, evidence for actual water on the surface of Mars remained frustratingly elusive. However many more lineae are subsequently discovered at similar midsouthern latitudes. In 2015 scientists use the CRISM spectrometer to find the next best thing – the distinctive signature of freshly formed hydrated minerals (chemical compounds with water locked into their structure). The minerals are found in association with various lineae, including those in Hale Crater (which is pictured here), and the signals are at their strongest where the lineae are widest and darkest. They are thought to be formed by perchlorate salts, which could act as natural antifreeze and keep water flowing at temperatures as low as -70º C (-94ºF).
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© NASA; JPL-Caltech; University of Arizona; Hubble; ESA
17 May 2015 MRO snaps a “Hollywood movie site”
After MRO’s confirmation of carbonate minerals on Mars in 2008, the hunt was on to discover larger deposits. The weathering process that creates carbonates also locks away carbon dioxide from the atmosphere, and so weathering could have played a significant role in thinning the Martian atmosphere. In 2015, scientists identify the largest carbonate region so far in Nili Fossae – exposed carbonates are coloured green in this composite of CRISM data and a HiRISE image. The presence of large carbonate deposits supports the idea that ancient surface water was amenable to the development of life.
Solar System From the Kármán line to beyond the orbit of Pluto 62 Think you know our Sun? We're still in the dark when it comes to knowing everything about our star
72 Exploring Venus Our nearest neighbour in space is also the most hostile planet in the Solar System
76 Strangest moons in the Solar System Some of the most fascinating worlds in our cosmic neighbourhood are orbiting moons
84 Ceres uncovered We relive what we've discovered from NASA's Dawn mission so far
“Dawn is the only spacecraft ever to orbit any two extraterrestrial destinations”
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Saturn's largest moon 60
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Inside the Sun
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Dawn's discoveries
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© Science Photo Library; NASA; SDO
Explore our nearest neighbour
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Solar System
Carved on the walls and sarcophagi of the pyramids located at the vast ancient burial ground of Saqqara are mentions of Amun, the Ancient Egyptian god of creation. He was thought to reside inside the Sun and his role in Egyptian life became very important as a result. But only when he was later combined with the Sun god Ra to become the God of Kings, did he rise to be the most worshipped ruler of them all. He was, as the Hymn to Amun-Ra describes him, the “Lord of things that are” and it was recognition of the Sun’s power as much as anything else. Fast forward to today though, and we know one thing for certain: no being – whether real or mythical – actually lives inside the Sun. Indeed, we understand that the Sun is one of billions of stars in the universe and that it has a surface temperature of 5,500 degrees Celsius (9,932 degrees Fahrenheit). We are certain that it has a radius just over 100 times that of Earth and that it’s at the centre of our Solar System. And yet we don't know everything, which is why recent studies casting fresh light on the scorching yellow dwarf have been intriguing many a scientist. “The observations of late have put a lot of theories under pressure,” says Dr Scott McIntosh, director of the High Altitude Observatory at the National Center for Atmospheric Research in the US. “That, I have to say, is a very good thing because unlike any other star in the universe, we can observe the living life out of this one and, for me as a solar physicist, if we don’t try and understand the star that is on our doorstep, then we haven’t a hope of understanding the others.” Over the past two decades, great strides have been made towards furthering our understanding of the Sun, from the launches of SOHO and STEREO – the former recently celebrated its 20th anniversary and the latter coming up to a decade of operation – to the Solar Dynamics Observatory (SDO) which launched in 2010. SDO’s mission is to unlock the processes inside the Sun, on the Sun’s surface and in its corona by using the most advanced spacecraft ever designed to study the star’s behaviour. In combination with other observational techniques, scientists have been able to view incredible phenomena, which allows them to better understand the Sun’s electromagnetic patterns and learn more about the space weather experienced here on Earth. “It’s really enabled a lot of cutting edge research,” says Dr McIntosh. Some of the observations are visually mindblowing. In September last year, the SDO not only captured a close-up of plasma loops on the Sun’s surface, but it also captured an image of the Earth and Moon as they crossed the face of the Sun – a rare double eclipse. In October, a huge coronal hole was revealed on the Sun’s surface, a temporary “symptom” of the magnetic field reaching out into space rather
The Solar Dynamics Observatory launched on 11 February 2010 in a bid to reveal the Sun’s inner workings
Discoveries of the Sun Our understanding of our star has continued to grow as technology has advanced 64
Circa 20 BCE
968 CE
Moon’s role in eclipse explained
Solar corona is described
Chinese astronomer Liu Hsiang noted that solar eclipses were caused by the Moon moving across the Sun and blocking it out.
The Byzantine historian Leo Diaconus was aged 18 when he described the solar corona as ‘a dim and feeble glow’.
Think you know our Sun?
A coronal hole in the Sun is a sign of an open magnetic field at a pole
A false-colour image of coronal loops taken with NASA’s Transition Region and Coronal Explorer satellite on 9 November 2000
than looping on to the surface, allowing solar winds to be ejected faster than on other parts of the Sun. In that instance, the hole was 50 times the size of Earth. But the scientific advancements have been more impressive. In February last year, NASA’s Deep Space Climate Observatory (DSCOVR) was launched to measure solar winds, replacing the ACE research satellite as the main warning system for solar magnetic storms. In November, the Mars Atmosphere and Volatile Evolution (MAVEN) mission showed that Mars may well have been hit by a solar storm which stripped away the planet’s upper atmosphere. But it’s no real surprise to hear that the Sun can be a wrecker. A lot of recent discoveries have centred on the star’s potential impact on Earth and the wider Solar System. Before we get to them, let’s quickly look at the workings of the Sun, starting with its primary make up: 72 per cent hydrogen and 26 per cent helium, with trace amounts of heavier elements such as carbon, oxygen and neon. Within the Sun’s dense and highly-pressurised core, hydrogen atoms smash
into each other at speed, fusing the nuclei while producing heat and helium. Such nuclear fusion – the exact principle which chillingly inspired the atomic bomb – sends energy outwards, causing photons to bounce around the Sun’s radiative zone, some 350,000 kilometres (220,000 miles) thick, before making their way to the convective zone where they zip along to the surface. The heat and light leave the Sun to travel towards the planets, reaching Earth after just eight minutes, providing us with warmth and daylight. This is great for sunseekers and those who don’t eat enough carrots, but ferocious activity on the solar surface has made solar physicists rather wary. The exterior of the Sun is in constant turmoil, hallmarked
“Superflares could take place once every 500 or 600 years on Earth and could cause long-term blackouts” Chloe Pugh
1609
1645
Galileo sheds light on sunspots
Maunder studies the magnetic cycle
Galileo Galilei built his first telescope, which allowed him to observe sunspots and confirm that the Sun rotates.
Edward Maunder photographed and measured sunspots, discovering the solar latitudes at which they occurred had regular variation over 11-year cycles.
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by solar flares of radiation that include white light, ultraviolet, X-rays and gamma rays, as well as coronal mass ejections (CMEs), which – put simply – are the casting of magnetic bubbles of charged particles into space. There may also be a new type of solar ejection that was discovered last year: large wave fronts in the Sun’s atmosphere together with energetic particle emissions rich in helium-3. “The new phenomenon is like a kind of explosion,” says Radoslav Bucik, head of the research team at the Max Planck Institute for Solar System Research (MPS), Johns Hopkins University, and NASA’s Jet Propulsion Laboratory in the United States. Such explosions can have an effect on Earth. They occur across the Sun thanks to a copious number of magnetic poles causing the plasma to rotate at different speeds in an act referred to as differential rotation. With some areas magnetically stronger than others, the field lines become twisted, usually above sunspots in the low solar atmosphere. Despite an energy equivalent of 100 million megaton bombs, most resulting flares pass off without major consequence for us. But with the recent discovery of possible superflares by a team at the University of Warwick on the binary star KIC 9655129, that could change: if such a superflare occurred on our Sun, it would pack the power of one billion megaton nuclear bombs. Lead scientist Chloe Pugh says superflares could take place “once every 500 or 600 years” on Earth and there is a very real possibility that they could cause long-term blackouts. The study was based on the observations of 23 stars and Pugh says more Sun-like stars need to be observed to improve the estimate. She adds, that “there is evidence of past superflares occurring on the Sun during 774CE and 993CE in ice cores” and should the Earth be in the direct path of a superflare, then it would be very disruptive. “For the Earth, the atmosphere protects us from most of the harmful ultraviolet and X-ray radiation from flares, however, the radiation can alter the chemistry of the upper atmosphere, damage the ozone layer, and disrupt radio communications,” Pugh tells us. Although she stresses that the Earth’s magnetic field can protect us from the worst of the charged particle radiation, for powerful solar storms some radiation can enter the atmosphere around the magnetic North and South Poles. “This would be hazardous for aircrew and passengers flying at high latitudes, and strong currents could be induced in power grids, causing large-scale power blackouts – this happened in 1989 in Quebec. In the nearEarth environment, satellites could be permanently damaged, or broken completely, and any astronauts in space would be in danger from radiation if there was not sufficient protection in their spacecraft.”
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How the Sun affects us As hot as it is, our star’s activities could so easily leave us cold Damage to electronics Solar flare protons as well as energetic electrons are able to cause damage to the electronics of spacecraft, disrupting their systems.
Earth’s natural defence Solar storm clouds are made up of charged particles, which are diverted around our planet thanks to the Earth’s magnetic field.
1800
1859
Infrared and ultraviolet radiation
Solar flare is recorded
William Herschel discovered heat rays – infrared radiation as it became known – and the following year Johann Wilhelm Ritter found “chemical rays”, now known as ultraviolet radiation.
Astronomers Richard Carrington and Richard Hodgson observed and recorded a solar flare. A huge geomagnetic storm was experienced on Earth.
SOHO Mission Launched in 1995, the Solar and Heliospheric Observatory (SOHO), contains 12 instruments which study the Sun from its deep core to the outer corona and solar wind. It gives up to three days notice of Earth-directed disturbances.
Aircraft disruption The solar flare protons can cause unwanted radiation effects on aircraft, and can also disrupt GPS signals. In 2012, Delta Airlines diverted some of its aircraft away from polar routes due to solar storms.
Think you know our Sun? A coronal loop Magnetism drives the mammoth explosions on the Sun, resulting in phenomena such as these enormous, arching, coronal loops of hot plasma. They usually connect sunspots and they flow along the curves of magnetic fields.
Emitting flares
Coronal mass ejections
Flares occur when the magnetic field lines switch to a lower energy configuration, called magnetic reconnection, and release vast amounts of energy in the process.
The magnetic loops twist and kink, storing the free magnetic energy, which produces a slinky shape. When the energy is released, the mass is ejected as a CME.
STEREO observatories Two observatories give a twin viewpoint to better understand the causes and mechanisms of CMEs. It allows for more accurate alerts – essential when CMEs are blowing 10bn tons of the Sun’s atmosphere at 1.6mn km/h (1mn mph) towards Earth.
Satellite disruption As a solar flare emits its outburst of electromagnetic radiation, the Earth’s atmosphere is ionised by X-rays and ultraviolet light. The disturbance to the Earth’s ionosphere is able to affect radio communication.
Exposing astronauts to radiation Blowing power grids CMEs cause electromagnetic fluctuations in the Earth’s atmosphere, which can induce fluctuations at ground level and blow out power grid transformers.
The Sun’s breakthrough Unfortunately, some particles are able to get through and charge the Earth’s upper atmosphere. The interactions between solar wind, the Earth’s magnetic field and its atmosphere causes the auroras that we witness near the poles.
1919
1951
General theory of relativity
Solar wind found to exist
Einstein’s theory was tested by Arthur Eddington during a total solar eclipse and proved that light could be bent by the gravitational force of the Sun.
Ludwig Biermann observed comet tails and noted the role of solar winds, which are charged gas particles ejected from the Sun.
One of the worries is that astronauts are exposed to potentially lethal or harmful doses of radiation but, thankfully, most solar protons cannot penetrate the ISS’s hull. Astronauts are also protected by the Earth’s protective magnetic field but they are vulnerable when performing Extra Vehicular Activities.
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Such phenomena are taken very seriously. The White House’s National Science and Technology Council has a National Space Weather Action Plan outlining a response to a solar storm and at the end of 2015, the US Department of Energy’s Princeton Plasma Physics Laboratory reported that it may have identified the mechanism which halts CMEs before they leave the Sun. CMEs tend to release magnetic energy into the Solar System, although they can also collapse back towards the Sun. Associate research physicist Clayton Myers has found that this is determined by whether or not the guide magnetic field is strong enough to prevent the energy from being released. By looking out for these guide fields, solar physicists will be able to better predict whether
an eruption is real or a false alarm. It also highlights that scientists still have so much to discover about our Sun. “While we understand the basics of most solar phenomena, there is a lot that is not well understood,” confesses Chloe Pugh. “For example, we cannot directly see the interior of the Sun, and so cannot determine exactly how the magnetic field is
“If we don’t understand the star that is on our doorstep, then we haven’t a hope of understanding the others” Dr Scott McIntosh
ESA’s Space Situational Awareness Space Weather Coordination Centre opens at the Space Pole, Brussels in 2013
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generated. Also, it is not known why the atmosphere, or corona, of the Sun is much hotter than the surface of the Sun – this is known as the coronal heating problem. A mystery of solar flares is the fast reconnection problem, where models of magnetic reconnection suggest a timescale that is much too slow to explain flares, which occur on a much faster timescale. There have been some models proposed to
1995
2005
SOHO is launched
Decade of SOHO discoveries
Following the launch of the SOHO satellite, it was discovered that coronal mass ejections (CMEs) occur each day.
In taking the most detailed measurements of the Sun’s surface, SOHO found that CMEs blast a “highway” through space.
Think you know our Sun?
Solar Probe Plus is set to go closer to the Sun than any spacecraft has ever gone
SOHO’s ultraviolet telescope captured the climax of this solar flare burst in 2003
2006
3D imaging of the Sun STEREO allowed 3D images to be taken of the Sun for the first time, while the Solar Dynamics Observatory launched in 2010.
explain all of these problems, but it can be difficult to prove which are correct.” The coronal heating problem has puzzled solar physicists since 1939. They cannot say for certain why the corona – the outermost part of the Sun’s atmosphere – is hotter than the surface of the Sun. But they have narrowed it down to magnetohydrodynamic waves, which travel from the core with the consequence of heating up the coronal plasma and the possibility of the magnetic field reconnecting in the corona causing nanoflares. In December 2014, NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) focussed on the Sun and noted the emission of high-energy X-rays, the likes of which are seen from black holes. Such X-rays would be generated from nanoflares and it confirmed the 2007 finding of X-ray jets spraying out hundreds of times each day at 3.2 million kilometres (two million miles) per hour. Observed by Japan’s Hinode spacecraft, it too was seen to help explain the superheating of the Sun’s corona. Further to that though, in 2013, Michael Hahn and Daniel Wolf Savin from Columbia University’s Astrophysics Laboratory observed a polar coronal hole where magnetic field lines stretch from the surface of the Sun into space. They saw that magnetic waves – called Alfvén waves – contain sufficient energy to heat the corona and that, because they deposit the energy at a low height, the heat is able to spread. But how they convert the energy has been unknown. In September 2015, Dr Hahn and Dr Savin became excited by observations made by teams at Nagoya University and the National Astronomical Observatory (NOS) in Japan. They saw resonant absorption, which is a wave process in which repeated waves add energy to the plasma. A certain type of plasma wave was being converted to a more turbulent type of motion and the resulting friction and electric currents were heating the solar material. “For over 30 years, scientists hypothesised a mechanism for how these waves heat the plasma,” said Dr Patrick Antolin of the NOS. “An essential part of this process is called resonant absorption – and we have now directly observed resonant absorption for the first time.” But the trick to making sense of many of the Sun discoveries is to bring them together as a whole, which is why some solar physicists tend not to look at one particular aspect of the Sun but at the star in general. “Instead of looking at the spots, flares and coronal mass ejections and treating them all individually like a dermatologist, I’m a GP and look at the whole Sun and how the atmosphere connects,” says Dr McIntosh. “It’s like playing KerPlunk – if a piece of magnetic field somewhere on the farside changes, it has a catastrophic affect on the piece facing Earth,” he adds. “This is a realisation largely born from the cutting edge ‘all of the Sun, all of the time’ observations of the past decade.” Yet the fact that it’s hard to directly observe much solar phenomena makes life difficult. “The fact that the Sun has a dynamo is questioned because we can't directly observe it, for example,” he says, of the physical process which is said to generate the Sun’s magnetic field. But here too, there have been some strides.
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The Sun outputs 385 billion billion megawatts of energy. It dwarfs Earth’s most powerful nuclear power station, KashiwazakiKariwa Nuclear Power Plant, which has a net capacity of 7,965 megawatts.
The distance between the Sun and the Earth is 150mn km (93mn mi) – you would have to drive around the Earth over 3,700 times to match it.
The Sun's core is 15,000,000ºC (27,000,000ºF) – about 4,000 times the melting point of a diamond.
Over one million Earths could fit inside the Sun – as could nearly 1,000 Jupiters.
Earth receives around 15 billion trillion joules of solar energy each day – roughly equivalent to 10,000 times global daily energy consumption.
A bolt of lightning can reach a temperature of 29,727ºC (53,540ºF) – around fives times the surface temperature of the Sun!
All about the
Sun Interesting facts that will shed more light on your knowledge of our star
You would need about four trillion trillion 100-watt lightbulbs to equal the brightness of the Sun.
The Sun’s plasma is the same state of matter as the substances found in fluorescent lights and plasma TV screens.
Solar winds travel at around 400 km/s (250 mil/s). The fastest recorded wind gust on Earth was taken during Cyclone Olivia in 1996. It was 0.11km/s (0.07mi/s).
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The Sun is 4.6 billion years old. The oldest tools found on Earth are around 3.3 million years old.
When the Sun emits a solar flare, on average the amount of energy released is equivalent to 100 million megaton hydrogen bombs all exploding at the same time.
Think you know our Sun?
predicts that the two waves will become increasingly offset during what is called Cycle 25, which starts in 2020. By Cycle 26 in 2030, the waves will be completely out of sync and they will separate into the hemispheres, ceasing to interact, thereby cancelling each other out. “Solar activity will fall and you will have this Maunder Minimum which we saw in the 17th century for 60 years from 1645,” Dr Zharkova tells us, referring to a period in history known for its mini ice age – the Little Ice Age. “At that time, there was a freeze and something similar could happen next time. But how it could decrease I cannot say yet. It is only a calculation.”
Indeed, it may well be that many of the current theories are blown out of the water when the Solar Probe Plus is launched in 2018. It is set to go closer to the Sun than any other spacecraft ever launched, protected by a heat shield that can survive 1,371 degrees Celsius (2,500 degrees Fahrenheit) and blasts of radiation. It would allow scientists to determine the structure and dynamics of the magnetic fields at the sources of solar wind and trace the flow of energy that heats the corona and accelerates the solar wind. “It’s a good development,” says Dr McIntosh. “When you think this star on our doorstep could literally wipe us out, and will do eventually, you can’t really gamble.”
“If a piece of magnetic field on the Sun’s farside changes, it has a catastrophic affect on the piece that's facing Earth”
© Adrian Mann; NASA; SDO; Pat Corkery; United Launch Alliance; AIA; STEREO, Johnny Henriksen; ESA; SOHO; JHUAPL; Goddard Space Flight Center; Royal Observatory Belgium
Our Sun has long been found to have an 11-year activity cycle, producing electric currents according to the flow of the Sun’s hot, ionised gases. At the peak of each cycle, scientists witness lots of sunspots and solar flares together with a number of coronal mass ejections, which is the casting into space of magnetic bubbles of charged particles. Yet we are still far from a complete understanding of how the dynamo works, and scientists have been frustrated that models have been unable to fully account for all of the Sun’s behaviour. During 2015, however, Professor Valentina Zharkova, from Northumbria University, found the irregular 11-year heartbeat may be produced by not one but two dynamos, one close to the surface and the other within the convection zone. The model shows magnetic wave components appearing in pairs, both with the same frequency, yet offset so that they fluctuate between the northern and southern hemispheres, and Dr Zharkova says it has proved to be accurate to 97 per cent. Using the model, she
It is important to keep check on space weather to protect astronauts on Extra Vehicular Activities (EVAs)
The SDO is able to take high-resolution photos and readings from within the Sun. It can also measure magnetic field activity
A CME captured by two instruments shows the eruption from its base
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Solar System
Exploring Venus
Lakshmi Planum
Our nearest neighbour in space is also the most hostile planet in the Solar System
After the Moon, Venus is usually the brightest object in Earth’s night sky – a brilliant morning or evening ‘star’ usually seen either in the east before sunrise or in the west after sunset. Its perpetual loose attachment to the Sun is due to the relative positions of planets in the inner Solar System – as the second planet, Venus’s orbit lies a little way inside Earth’s, so it always lies in roughly the same direction as the Sun itself. For most of the time, Venus is the closest major planet to Earth, and what’s more, it is also Earth’s near-twin in terms of size. So it might seem reasonable to expect Earth and Venus to have a lot in common – but this is where the similarities end. For centuries astronomers and writers speculated that Venus might have a tropical climate and even alien life – but today, the planet named after the goddess of beauty is often considered ‘Earth’s evil twin’. This changed reputation is largely due to the space-age discovery of Venus’s scaldinghot, dense and toxic atmosphere. The highly reflective white clouds that shroud the planet
How to get there 1. Leaving Earth While a manned Venus mission could theoretically launch direct from Earth, it’s more likely to be assembled in Earth orbit and to leave from there with a single controlled rocket burn.
boost its brightness as seen from Earth, but their composition – a mix of sulphur dioxide and sulphuric acid droplets – is highly corrosive. What’s more, the atmosphere is dominated by carbon dioxide, and its surface pressure is about 93 times greater than that on Earth. The atmosphere traps heat close to the ground, resulting in surface temperatures of around 460 degrees Celsius (860 degrees Fahrenheit) – hotter even than those on Mercury – so any space traveller stepping onto the surface would require a heavily armoured spacesuit to prevent themselves being simultaneously crushed, boiled and choked. Climate scientists believe that Venus owes its present climate to the disappearance of water early in its history, followed by a runaway greenhouse effect as carbon dioxide built up in the atmosphere. What’s more, the absence of water may also be responsible for the fact that Venus lacks tectonic plates like those on Earth, resulting in the extraordinary geology hidden beneath the toxic clouds.
3. Towards the Sun
The distance between Earth and Venus varies wildly depending on where the planets sit on their orbits. Close approaches occur every 584 days, at which time the two worlds are separated by about 40 million kilometres (25 million miles).
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4. Arrival at Venus
With current technology, it’s possible to reach Venus in about four to five months – for the shortest journey along part of a spiral curve, Earth departure would need to take place a couple of months before the date of closest approach.
2. Shifting alignments
Heng-O Corona
Venus moves along its orbit at a speed of 35 kilometres (22 miles) per second – about five kilometres (three miles) per second faster than Earth – but the transfer between orbits and momentum gained during the journey towards the Sun makes it fairly easy to match speeds.
5. Adjusting orbit After an initial retro-rocket burn slows the spacecraft down and puts it in a wide elliptical orbit, further adjustments can be made by aerobraking (using friction with the upper atmosphere to lose energy and drop into a lower orbit).
Exploring Venus
How big is Venus? With an equatorial diameter of 12,100 kilometres (7,520 miles), Venus is just 638 kilometres (396 miles) smaller than Earth (roughly five per cent).
Maxwell Montes Ishtar Terra
Venus
12,100km (7,520mi) wide
Earth
Eistla Regio
Aphrodite Terra
Venus
Alpha Regio
How far is Venus? The distance to Venus varies hugely depending on its position relative to Earth. At its closest approach Venus can be just 38.2 million kilometres away (23.7 million miles), while at its most distant it can be up to 261 million kilometres (162 million miles) from Earth.
Venus
Earth
64m (210ft) apart at their closest if both planets were marble-size 73
Solar System
Top sights to see on Venus While Earth’s surface is shaped by a wide variety of geological forces – such as plate tectonics and erosion, the Venusian landscape is almost entirely shaped by volcanism. Venus is home to a much greater variety of volcanic features than those seen on Earth. The largest, just as on Earth and Mars, are volcanic ‘shields’ – shallow-sloped mountains formed where lava has erupted through vents in the surface over millions of years, solidifying in layers. However, Venusian shield volcanoes can grow more than ten times larger than those on Earth. This is because Venus’s crust seems to be a single mass rather than an Earth-like jigsaw of shifting plates, so volcanic ‘hotspots’ in the underlying mantle stay in the same place relative to the crust instead of slowly drifting
over time. The biggest shields are concentrated in two large highland regions – Aphrodite Terra near the equator, and Ishtar Terra near the north pole. Rolling lava plains, formed by material erupted from the shields, cover more than half of the surface, while lower-lying areas are relatively smooth, filled in with material slowly eroded by the harsh climate. Stratovolcanoes (the relatively small volcanic cones familiar on Earth) are absent, but there are several uniquely Venusian volcano types – flat-topped ‘pancake domes’, scallop-edged ‘ticks’, radiating fissure patterns called ‘novae’, and web-like ‘arachnoids’. Deep, winding chasms, particularly to the south of the equator, look like tectonic rifts found on Earth, but in fact they are faults created as the
surface cracked apart due to upward or downward pressure on neighbouring volcanic regions. Venus’s thick atmosphere protects the surface from all but the largest incoming space rocks – as a result the planet has relatively few impact craters. The number and distribution of craters can still be used to estimate the age of different parts of the Venusian surface, however, and reveals that the entire planet was resurfaced in a period of catastrophic volcanism around 500 million years ago. One possible explanation is that while Earth’s plate tectonics allow a steady release of heat from the mantle, Venus’s solid crust produces a ‘pressure cooker’ effect in which heat gradually builds up until it finally escapes in a series of worldwide eruptions.
Active volcanoes?
Triple crater
Spiders from Venus
While no one has yet caught a Venusian volcano in the act of eruption, the detection of fresh ash around hot volcanic peaks – such as Idunn Mons shown here – suggests activity in the geologically recent past.
Venus’s most spectacular impact feature is the Danilova group – a trio of craters each about 50km (31mi) wide, formed when a single incoming meteoroid broke up in the atmosphere.
Arachnoids combine concentric rings and radiating fractures to form a pattern like a spider’s web. They may be created when rising volcanic material pushes the crust upwards, and later subsides.
Maat Mons The second highest volcano on Venus, Maat Mons rises some 8km (5mi) above the average Venusian surface level, forming a peak within the broad plateau of Aphrodite Terra.
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Exploring Venus
Venus’s orbit Venus orbits the Sun every 224.7 days at an average distance of 108.2 million kilometres (67 million miles). However it spins on its axis every 243.7 Earth days, so its day is significantly longer than its year. What’s more, Venus spins in the opposite direction to any other planet, so according to some conventions, its poles are actually upside down relative to the other planets of the Solar System. Because its axis of rotation is almost upright compared to its orbit, Venus lacks any significant seasons.
117 Earth days = 1 Venus solar day
117
1 Earth year = 365 days 1 Venus year = 224.7 Earth days 0 Sun
Rotation
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Venus in numbers
224.7
Weather forecast Venus’s weather hardly changes due to the
effect of its thick atmosphere and 464°C oppressive its lack of seasons. Winds at the surface are and while the clouds are thought 867.2°F sluggish, to rain sulphuric acid, this evaporates before it reaches the surface. The planet’s slow rotation allows the atmosphere to redistribute heat, making Venus’s night side just as hellish as its daylit side. Ultraviolet images reveal huge chevron-shaped cloud features moving slowly in the upper atmosphere.
Time taken in Earth days for Venus to orbit the Sun
Tilt of Venus’s axis of rotation relative to the plane of its orbit
Strength of Venus’s surface gravity relative to Earth’s
464°
Average surface temperature in Celsius – hotter than Mercury
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2.64° 0.905 96.5%
Percentage of carbon dioxide in Venus’s atmosphere (compared to Earth’s 0.04%)
Venus’s rotation period in Earth days – longer than its year
1.92 Length of a year on Venus in terms of its ‘solar day’ – the time between successive sunrises
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© Freepik.com; NASA
Venus rotates in the opposite direction to any other planet in the Solar System
Solar System
STRANGEST
MOONS IN THE SOLAR SYSTEM Some of the most fascinating worlds in our cosmic neighbourhood are not planets, but the moons that orbit around them All but two of our Solar System’s planets have satellites of one sort or another. Earth’s own Moon, a beautiful but stark, dead world shaped by ancient volcanoes and countless impact craters, is undoubtedly the most familiar, but it’s far from being the most interesting – each of the outer Solar System’s giant planets is accompanied by a large retinue of satellites, many of which formed at the same time and from the same ice-rich material as the planets. Although far from the Sun and starved of solar heat and light, they nevertheless show as much variety as the planets themselves. All About Space takes a trip to visit some of the strangest and most exciting of these astonishing worlds. Some, such as Jupiter’s Callisto and Saturn’s
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Mimas, have been frozen solid for billions of years but bear extraordinary scars from exposure to bombardment from space. Others, such as Saturn’s shepherd moons Pan and Atlas and Neptune’s lonely Nereid, have been affected throughout their history by interactions with their neighbours. Most excitingly, some have been heated by powerful tidal forces from their parent planets, triggering phases of violent activity like those which shaped Miranda, Uranus’ Frankenstein moon. In some cases, these forces are still at work today, creating fascinating bodies such as Jupiter’s tortured Io and Saturn’s icy Enceladus, whose placid exterior may even hide the greatest secret in the Solar System: extraterrestrial life itself.
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Solar System
A Ring Saturn’s brightest ring is the A Ring, divided by the narrow Encke Gap. The ultra-fine F Ring runs around its outer edge.
E Ring
Orbit of Enceladus
The E Ring is a broad, largely transparent ring of scattered icy particles.
Enceladus’ orbit around Saturn coincides with the densest part of the E Ring.
Geyser faults Tidal forces create a liquid water ocean that erupts as icy plumes along weak fault lines in the southern hemisphere, known as ‘tiger stripes’.
Inner rings The broad Cassini Division separates the A Ring from the inner B, C and D Rings.
Fragmented material Small ice fragments trailing behind Enceladus are ground down into ever-finer particles as they orbit Saturn.
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Enceladus
The ring bearer
Since NASA’s Cassini probe arrived at Saturn in 2004, the ringed planet’s small inner satellite, Enceladus, has become one of the most intensely studied and debated worlds in the entire Solar System. It owes its newfound fame to the discovery of huge plumes of water ice erupting into space along fissures in its southern hemisphere – a sure sign of liquid
Callisto’s surface has remained essentially unchanged for over 4.5 billion years
Mass: 1.1 x 1023kg (2.4 x 1023lb) Diameter: 4,821km (2,996mi) Parent planet: Jupiter Discovered: 1610, Galileo Galilei
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Mass: 1.1 x 1020kg (2.4 x 1020lb) Diameter: 504km (313mi) Parent planet: Saturn Discovered: 1789, William Herschel
water lurking just beneath the moon’s thin, icy crust. The strange activity of Enceladus was suspected before Cassini’s arrival thanks to earlier images that showed the moon has an unusually bright surface and craters that look like they are blanketed in snow. Nevertheless, the discovery of the ice plumes (initially made when
Cassini flew straight through one) was a spectacular confirmation that Enceladus is an active world. With a diameter of 504 kilometres (313 miles) and a rock/ice composition, Enceladus should have frozen solid billions of years ago, like many of its neighbours in the Saturn system. But tidal forces caused by a tug of war between Saturn and a larger moon,
2 Callisto
Dione, keep the moon’s interior warm and active, making it a prime target in the hunt for life in the Solar System. While much of the water ice falls back to cover the surface, a substantial amount escapes from the weak gravity and enters orbit around Saturn. Here, it spreads out to form the doughnutshaped E Ring – the outermost and sparsest of Saturn’s major rings.
The most cratered world
The outermost of Jupiter’s Galilean moons, Callisto is the third largest moon in the Solar System and is only slightly smaller than Mercury. Its main claim to fame is the title of most heavily cratered object in the Solar System; its dark surface is covered in craters down to the limit of visibility, the deepest of which have exposed fresh ice from beneath and scattered bright ‘ejecta’ debris across the surface. Callisto owes its cratered surface to its location in the Jupiter system – the giant planet’s gravity exerts a powerful influence, disrupting the orbits of passing comets and often pulling them
to their doom (most spectacularly demonstrated in the 1994 impact of Comet Shoemaker-Levy 9). Jupiter’s larger moons are directly in the firing line and end up soaking up more than their fair share of impacts, but Callisto’s inner neighbours – influenced by greater tidal forces from the planet – have all experienced geological processes that wiped away most of their ancient craters. Callisto’s surface, however, has remained essentially unchanged for more than 4.5 billion years, developing its dense landscape of overlapping craters over aeons of time.
Strangest moons in the Solar System
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Io
Mass: 8.93 x 1022kg (1.97 x 1023lb) Diameter: 3,643km (2,264mi) Parent planet: Jupiter Discovered: 1610, Galileo Galilei
The cold inferno
Io is the innermost of the four giant Galilean moons that orbit the Solar System’s largest planet, Jupiter. But while the outer three are (at least outwardly) placid frozen worlds of rock and ice, Io’s landscape is a virulent mix of yellows, reds and browns, full of bizarre and everchanging mineral formations, created by sulphur that spills onto its surface in many forms. In fact, Io is the most volcanic world in the Solar System. Io’s strange surface was first observed during the Pioneer space probe flybys of the early 1970s, but its volcanic nature was only predicted
weeks before the arrival of the Voyager 1 mission in 1979. The moon is caught in a gravitational tug of war between its outer neighbours and Jupiter itself, and this prevents its orbit from settling into a perfect circle. Instead, small changes in Io’s distance from Jupiter (less than 0.5 per cent variation in its orbit) create huge tidal forces that pummel the moon’s interior in all directions. Rocks grinding past one another heat up due to friction, keeping the moon’s core molten and creating huge subsurface reservoirs of molten magma.
While the majority of Io’s rocks are silicates similar to those on Earth, these have relatively high melting points and so are mostly molten in a hot magma ocean that lies tens of kilometres below the surface – most of Io’s surface activity, in contrast, involves sulphur-rich rocks that can remain molten at lower temperatures. Together, these two forms of volcanism have long since driven away any icy material that Io originally had, leaving a world that is arid and iceless despite an average surface temperature of -160 degrees Celsius (-256 degrees Fahrenheit).
Volcanic Io and its parent planet Jupiter, photographed by NASA’s New Horizons space probe in 2007
Zal Montes
Loki Patera Bosphorus Regio Prometheus
Media Regio
Pele
Colchis Regio Cullan Patera Babbar Patera
Tarsus Regio
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Solar System Cassini’s infrared camera pierces Titan’s atmosphere to reveal lakes around the moon’s north pole
Tiny Sun From Saturn, the Sun is ten per cent of the size as seen from Earth.
Weak sunlight Titan’s distance from the Sun and its thick atmosphere mean that the surface receives about one per cent of the sunlight that Earth receives.
Methane loss Methane evaporates from lakes back into the atmosphere.
Landscape runoff Methane rainfall onto highland areas runs downhill and collects in methane lakes.
Solid methane Methane frosts coat a landscape of rock and water ice.
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Titan
The second Earth
Saturn’s largest moon, Titan, is unique in the Solar System as the only satellite with a substantial atmosphere of its own – a discovery that frustrated NASA scientists during the initial flybys of the ringed planet, when images from the Voyager space probes revealed only a hazy orange ball. The Cassini orbiter, however, was fitted with infrared and radar instruments that pierced the opaque atmosphere for the first time, revealing a softened landscape of rivers and lakes that is unlike any other world in the Solar System except for Earth itself.
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Mass: 1.3 x 1023kg (2.9 x 1023lb) Diameter: 5,150km (3,200mi) Parent planet: Saturn Discovered: 1655, Christiaan Huygens
Despite being larger than the planet Mercury, Titan can only hold onto its thick atmosphere because of the deep cold found some 1.4 billion kilometres (0.9 billion miles) from the Sun (the moon’s average surface temperature is a freezing -179 degrees Celsius, or -290 degrees Fahrenheit). Titan’s atmosphere is dominated by the inert gas nitrogen (also the major component of Earth’s air) but it gets its distinctive colour, opaque haze and clouds from a relatively small proportion of methane (CH4). Amazingly, conditions on Titan
are just right for methane to shift between gaseous, liquid and solid forms, generating a ‘methane cycle’ rather similar to the water cycle that shapes Earth’s climate; in cold conditions, methane freezes onto the surface as frost and ice; in moderate temperatures, it condenses into liquid droplets and falls as rain that erodes and softens the landscape, before accumulating in lakes; while in warmer regions it evaporates and returns to the atmosphere. Titan experiences changing seasons very similar to those on our planet
(though its year is 29.5 Earth years long), and the temperatures at the winter pole seem to favour rainfall, so the lakes migrate from one pole to the other over each Titanian year. With all this activity, Titan is an intriguing target in the search for extraterrestrial life, though most biologists find it hard to envision organisms that could exist in such harsh and chemically limited conditions, and most agree that Titan’s watery inner neighbour Enceladus offers more promising prospects for life.
Strangest moons in the Solar System
Enhanced-colour view of Hyperion from Cassini
Giant planet Saturn’s huge bulk is largely hidden by a hazy atmosphere.
5 Hyperion
The spongy satellite
Hyperion is the strangest looking satellite in the Solar System, its surface resembling a sponge or coral with deep, dark pits rimmed by razor-sharp ridges of brighter rock and ice. But that’s not the only thing that’s strange about Hyperion; it was the first nonspherical moon to be discovered and has a distinctly eccentric orbit. Rather than matching its rotation to its orbital period, it spins in a chaotic pattern, with its axis of rotation wobbling unpredictably. Like all moons in the outer Solar System,
Methane lakes Methane rains out of the atmosphere at the winter pole to form large lakes.
Mass: 5.6 x 1018kg (1.2 x 1019lb) Diameter: 270km (168mi) Parent planet: Saturn Discovered: 1848, William Bond, George Bond and William Lassell
it’s mostly made of water ice but its surface is unusually dark. When Cassini flew past it measured its density to be 55 per cent that of water – its interior is mostly empty space. One popular theory to explain these weird features is that Hyperion is the surviving remnant of a larger satellite that once orbited between Titan and Iapetus, and which was largely destroyed by a collision with a large comet. Material that survived in a stable orbit then came together again to create Hyperion as we know it.
Pan photographed by Cassini amid Saturn’s rings
Titan Earth
Measuring up Titan Surface gravity 0.14
1.0
Day length in Earth days 16 1
Orbital period in Earth days 16 1
Temperature
0°C
-179°C (-290ºF) 14°C (57ºF)
Atmospheric pressure 1.5 bar 1.0 bar
Atmospheric composition 95% nitrogen 5% methane 78% nitrogen 21% oxygen 1% argon
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Pan and Atlas The flying saucers
Saturn’s moons Atlas and Pan are the smallest moons in the Solar System. But despite their size, their influence can be seen clearly from Earth in the form of the prominent ‘gap’ they create in the planet’s ring system. These two worlds are perhaps the best-known examples of shepherd moons – small satellites that orbit in or around the ring systems of the giant planets. As their name suggests, when coupled with the influence of distant outer moons, such satellites help to herd the particles orbiting in the ring system together, while ‘clearing out’
Mass: 4.9 x 1015kg (1.1 x 1016lb) and 6.6 x 1015kg (1.6 x 1016lb) Diameter: Average of 28km (17mi) and 30km (19mi) Parent planet: Saturn Discovered: 1990 and 1980, Voyager 2
others. Pan is responsible for creating the Encke Gap, a prominent division in Saturn’s bright A Ring, while Atlas orbits just outside the A Ring. But the most intriguing property of both worlds is their smooth shape, resembling a walnut or a flying saucer. Experts believe the moons are blanketed in small particles swept up as they keep the space between the rings clear. As most of the particles orbit in a plane one kilometre (0.6 miles) thick, they tend to pile up around each moon’s equator, building up a distinctive equatorial ridge.
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Solar System
A Cassini photomosaic of Iapetus reveals its bizarre two-tone surface
Dactyl’s orbit is still unknown – Galileo approached the asteroid in Dactyl’s orbital plane, so its images provided limited data
Ida Direction of orbit Dactyl orbits in the same direction as Ida’s rotation.
Close approach Computer models show that Dactyl can come no closer to Ida than 65km (40mi) for its orbit to remain stable.
Mass: 1.8 x 1021kg (4.0 x 1021lb) Diameter: 1,469km (913mi) Parent planet: Saturn Discovered: 1671, Giovanni Cassini
7 Iapetus
The walnut
The outermost member of the large family of moons that orbit Saturn, Iapetus has two distinct claims to a place in any list of weird satellites. The first became obvious when it was discovered in 1671 – the satellite is much dimmer when seen on one side of its orbit compared to the other. Iapetus, like most moons, keeps one face permanently towards its parent planet. Its leading hemisphere (the half that faces ‘forwards’ as it orbits Saturn) is dark brown, while its trailing hemisphere is light grey. One early theory to explain the colour difference was that the leading side is covered in dust, which is generated by tiny meteorite impacts on small outer moons, and spirals towards Saturn. However, images from Cassini reveal a more complex story – most of the dark material seems to come from within Iapetus, left behind as dark ‘lag’ when dust-laden ice from the moon’s surface sublimates (turns from solid to vapour). The process was likely started by dust from the outer moons accumulating on the leading hemisphere, but once it began, the tendency of the dark surface to absorb heat has caused a runaway sublimation effect. As if this weren’t strange enough, Iapetus is ringed by a mountainous equatorial ridge that is 13 kilometres (eight miles) high and 20 kilometres (12 miles) wide, giving the moon its distinctive walnut shape. The origins of this ridge are puzzling – some theories suggest it is a ‘fossil’ from a time when Iapetus span much faster and bulged out at the equator, while others think it could be debris from a ring system that once encircled the moon and collapsed onto its surface.
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Encounter distance Dactyl was about 90km (56mi) from Ida during Galileo’s flyby.
Range of possibilities
The most detailed view of Dactyl available
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Green tracks show a range of potential orbits that would fit Galileo’s observations.
Dactyl
The asteroid moon
The idea that small objects can have their own moons was brought home when NASA’s Jupiter-bound Galileo probe flew past the 60-kilometre (37mile) long, potato-shaped asteroid 243 Ida in 1993. Several images sent back from the asteroid belt showed a small, egg-shaped object positioned near Ida – a satellite soon named Dactyl. Ida’s moon is tiny, at just 1.6 kilometres (0.99 miles) on its longest axis. Thanks to the larger asteroid’s weak gravity, Dactyl is unlikely to
be an object captured into orbit, but the alternative – that Ida and Dactyl formed alongside each other – raises as many questions as it answers. Ida is a major member of the Koronis family of over 300 asteroids, all of which share similar orbits. The family is thought to have formed 1 or 2 billion years ago during an asteroid collision. A simple explanation is that Dactyl could be a smaller fragment of debris from the collision that ended up in orbit around Ida, but there is a problem – computer
9 Nereid
Mass: Unknown Diameter: 1.4km (0.87mi) Parent planet: Asteroid 243 Ida Discovered: 1993, Galileo space probe models suggest Dactyl would almost certainly be destroyed by an impact from another asteroid. So how can it be over a billion years old? One theory is that the Koronis family is younger than it appears, and Ida’s heavy cratering is due to a storm of impacts triggered in the original break-up. Another theory is that Dactyl has suffered a disrupting impact, but has pulled itself back together in its orbit – which might explain its surprisingly spherical shape.
Neptune’s boomerang
Voyager 2’s only glimpse of Nereid showed it as a distant blur of pixels
Discovered by astronomer Gerard Kuiper in 1949, Nereid was the second moon found to orbit Neptune, and its claim to fame arises from its extreme orbit. Nereid’s distance from Neptune ranges between 1.4 million and 9.7 million kilometres (850,000 and six million miles). This orbit is usually typical of captured satellites – asteroids and comets swept up into highly eccentric orbits by the gravity of the giant outer planets – but Nereid’s unusually large size suggests a rather more interesting story. Mass: 3.0 x 1019kg (6.6 x 1019lb) Diameter: 340km (211mi) Parent planet: Neptune Discovered: 1949, Gerard Kuiper
Neptune is striking as it does not have a normal family of satellites – a system of moons that formed in orbit around it and which circle in the same ‘prograde’ direction as the planet’s rotation. Instead though, a handful of small satellites survive in and around the planet’s rings and the system is dominated by a single large moon, Triton, which orbits in the wrong ‘retrograde’ direction. Evidence from Voyager 2’s 1989 flyby suggests that Triton was captured into orbit from the nearby Kuiper Belt (the ring of icy objects beyond Neptune). Triton would have disrupted the orbits of Neptune’s original moons, ejecting many of them. But many astronomers believe Nereid could be a survivor, clinging on at the edge of Neptune’s gravitational reach.
Strangest moons in the Solar System
10 Miranda
The chiselled satellite
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This Voyager image reveals Miranda’s varied surface, including towering cliffs at the lower right
Mimas
Mass: 3.8 x 1019kg (8.4 x 1019lb) Diameter: 396km (246mi) Parent planet: Saturn Discovered: 1789, William Herschel
The real-life Death Star
When NASA’s Voyager space probes sent back the first detailed images of Mimas in the 1980s, scientists and the public were shocked by its resemblance to the Death Star space station from the hugely successful Star Wars films. A huge crater (named after William Herschel, who discovered the moon in 1789)
dominates one hemisphere and is almost the exact size and shape of the planet-killing laser dish dreamt up by George Lucas many years before. But Mimas has more to offer than pop cultural references. Mimas is the innermost of Saturn’s substantial moons (orbiting closer than Enceladus, but further out than
Death Star crater If Mimas was scaled up to the size of Earth, its giant crater Herschel would be as wide as Australia. The crater was originally far deeper, but has slumped over time as Mimas’ icy surface has slowly levelled off.
Towering peak Herschel’s central peak rises 6km (3.7mi) above the crater floor – it’s as high as Mount Kilimanjaro in Africa and taller than any European mountain.
Crater variation Mimas’ surface is saturated with craters, but those around its south pole are half the size of those elsewhere (about 20km, or 12.4mi, at their biggest). This suggests the south pole was probably resurfaced with fresh ice early in Mimas’ history.
been shattered by an interplanetary impact, and whether this cataclysmic event might somehow be linked to Uranus’ own extreme tilt. Further studies, however, have shown that such a theory comes up short when trying to explain Miranda’s mix of surface features, and the right kind of impact is unlikely. Instead, it seems plausible that tidal forces are to blame. Today, Miranda follows an almost circular orbit, but in its past its orbit was in a ‘resonant’ relationship with larger moon Umbriel. This brought the two moons into frequent alignments that pulled Miranda’s orbit into an elongated ellipse that experienced extreme tidal forces. Pushed, pulled and heated from within, its surface fragmented and rearranged itself before the moons moved again and Miranda’s activity subsided.
Pan and Atlas), and with a diameter of just 396 kilometres (246 miles), it’s the smallest object in the Solar System known to have pulled itself into a spherical shape from its own gravity. Some larger Solar System objects haven’t quite managed this, and most astronomers agree that it’s only possible for Mimas because of
the moon’s low density (just 15 per cent greater than water). In fact, Mimas has such low density that the formation of Herschel shook it to the core – the giant crater is onethird the diameter of Mimas, and the impact which formed it would have been as violent as it could get without smashing the moon to pieces.
Cracked surface
@ NASA; Science Photo Library; ESO; JPL-Caltech; Space Science Institute; Lunar and Planetary Institute; USGS
Mass: 6.6 x 1019kg (1.5 x 1020lb) Diameter: 470km (292mi) Parent planet: Uranus Discovered: 1948, Gerard Kuiper
The smallest of five satellites known to orbit Uranus before the Voyager 2 flyby of 1986, Miranda is one of the strangest worlds in the Solar System. Voyager images revealed an extraordinary patchwork of terrains, seemingly put together at random. Some parts are heavily cratered, some relatively uncratered (indicating their youth as they have been less exposed to bombardment from space). One prominent feature is a pattern of concentric ovals resembling a racetrack while, elsewhere, parallel V-shapes form a chevron-like scar. An early theory to explain Miranda’s jumbled appearance is that it is a Frankenstein world – a collection of fragments from a predecessor moon that coalesced in orbit around Uranus. Astronomers wondered whether Miranda’s predecessor might have
Deep chasms 100km (62mi) long and 6km (3.7mi) wide were likely created in the formation of Herschel. Scaled up to the size of Mars, they would rival the Red Planet’s famous Valles Marineris canyon.
Colour changes Enhanced-colour images show slight variations in Mimas’ surface – a slightly greenish hue overlaid with blue in the area around Herschel.
Rugby ball moon Tidal forces pulling on Mimas have given it an ellipsoidal shape, with the axis pointing towards Saturn ten per cent longer than the axis from pole to pole. Slight wobbles in Mimas’ long axis suggest it may have a liquid water layer deep inside.
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Solar System
With the decision made for the Dawn spacecraft to continue studying the dwarf planet, we relive what we’ve discovered from the NASA mission so far
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Dawn’s science objectives ; Study the early Solar System via Ceres and Vesta ; Understand the building blocks of terrestrial planets ; Study the internal structure of Ceres and Vesta ; Determine surface shape and cratering on both ; Measure the mass, gravity, and rotation of both asteroids
; Determine their thermal history and the shape of their cores ; Understand the role of water in asteroid evolution ; Test the theory that some meteorites on Earth came from Vesta ; Extensively map the surface of both worlds
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Solar System
In science fiction, we are used to seeing spacecraft fly from one planet to another with ease. But in the real world, flying between two different objects in space is very difficult. Large amounts of fuel are needed to do so, something that just isn’t readily available to most of the relatively small probes that we have sent out into the cosmos. But in 2012, NASA’s Dawn spacecraft changed all that. Using a revolutionary ion engine, it became the first spacecraft ever to orbit two separate bodies aside from Earth, in this case two large asteroids (one technically a dwarf planet) in the asteroid belt: Vesta and Ceres. Is Dawn the science fiction spacecraft that we have all been waiting for? “Dawn is the only spacecraft ever to orbit any two extraterrestrial destinations,” Dawn’s mission director, Dr Marc Rayman, tells All About Space. “It is truly an interplanetary spaceship!” But the mission has only been possible thanks to the remarkable ion engine on board the spacecraft. Ion engines have long been touted as the future of space travel, or at least an important part of it. They provide a small but regular amount of thrust over time, theoretically allowing a spacecraft to change its speed – and thus travel
through space – more efficiently than the traditional, chemically-fuelled spacecraft from previous missions. NASA first toyed with ion engines in 1998, with the launch of their Deep Space 1 vehicle, which flew past an asteroid and a comet. At the turn of the century, they then began considering a more ambitious mission, Dawn, which would not just fly past objects, but orbit them. On the brink of cancellation, the mission was saved in 2006 and ultimately launched on 27 September 2007. The goal of the mission, aside from showing off the impressive capabilities of ion engines, was to peer into the history of the Solar System by examining two large bodies in the asteroid belt: Vesta and Ceres. Both are considered protoplanets, objects not quite big enough to form fully-fledged planets, but possibly
similar to the progenitors that gave rise to other worlds in our Solar System. And, compared to most other asteroids in the asteroid belt between Mars and Jupiter, they’re pretty big. While most asteroids are less than one kilometre (0.62 miles) in size, Ceres has a diameter of 950 kilometres (590 miles). This led to it being reclassified as a dwarf planet in 2006. Vesta, meanwhile, is an impressive 525 kilometres (326 miles) across. “Ceres itself has about a third of the total mass between Mars and Jupiter,” says Rayman. “While Vesta has about eight per cent [of the mass]. So the Dawn spacecraft has single-handedly explored about 40 per cent of the mass contained in the asteroid belt.” Vesta itself was first discovered back in 1807; Ceres was slightly earlier, in 1801. Dawn’s arrival in orbit at
“Dawn has single-handedly explored about 40 per cent of the mass contained in the asteroid belt” Dr Marc Rayman, Dawn mission director
Bright spots on Ceres had scientists baffled at first
Dawn created this colour-coded topographic map of the Occator Crater on Ceres. Blue is low and brown is high
The Occator Crater on Ceres contains some of the most famous bright spots, now believed to be salts
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Ceres uncovered On 9 June 2016, the Dawn team were presented with the National Aeronautic Association 2015 Robert J Collier Trophy for the success of the mission
“Dawn is the only spacecraft ever to orbit any two extraterrestrial destinations” Dr Marc Rayman, Dawn mission director Vesta on 16 July 2011, and at Ceres later on, made it the first spacecraft to visit these bodies, some 200 years after their discovery. To get to Vesta, Dawn was almost continuously firing its ion thrusters, something not possible for chemical spacecraft. To date, after almost nine years in space, Dawn has fired its ion thrusters for more than 5.5 years, setting a new record for powered spacecraft flight. Before Dawn arrived at Vesta, our best guess at its appearance came from three-dimensional models that were created using data from the Hubble Space Telescope. Dawn, though, with its onboard cameras, was able to reveal stunning views of this grey, rocky world for the first time. Truth be told, it’s perhaps not as exciting to look at as, say, the recently acquired New Horizons image of Pluto, but it’s still very interesting in its own right. Among its discoveries, Dawn revealed that Vesta more closely resembled terrestrial planets like Earth than other asteroids. Analysis also confirmed the theory that many meteorites on Earth originated from Vesta. We now know that we have more rock samples from Vesta than from the Moon, even
accounting for the samples brought back by the Apollo missions. Another fascinating discovery was a large depression on Ceres, the Rheasilvia basin, formed by a giant impact in Vesta’s past. It is more than 500 kilometres (310 miles) in diameter, and has a huge mountain at its centre twice the height of Mount Everest. The effects of the impact that formed it provide evidence that Vesta is indeed a protoplanet. “The energy of the impact reverberated through Vesta’s interior and formed a vast network of canyons hundreds of kilometres away,” explains Rayman. “If Vesta were a huge chunk of rock, that would not have happened. The mechanism depends on Vesta having a core, a mantle, and a crust – like a planet!” On 5 September 2012, after more than a year orbiting Vesta, Dawn used its ion engine to escape its gravity and began a 2.5-year journey to Ceres, located slightly further out in the asteroid belt. It arrived on 6 March 2015 and, with this being a few months before New Horizons’ arrival at Pluto, this made Dawn the first spacecraft to visit a dwarf planet. Being located further from the Sun has allowed Ceres to remain relatively wet and cool, compared to Vesta.
This layered crater lies inside Vesta's huge and fascinating Rheasilvia basin
Ahuna Mons, shown on the right, is the largest mountain on Ceres with a height of about 5km (3mi)
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Solar System
V
t rbi o s’ re bit r e o C ’s ta s e
Dawn’s journey
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rbit rs’ o Ma
bit ’s or rth Ea
01 09 08 02 04 03 07 06
1 Launch date
27 September 2007 The Dawn spacecraft is launched on a Delta II rocket from Cape Canaveral, Florida.
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2 Mars flyby
17 February 2009 Dawn flies within 549km (341mi) of Mars, gaining a gravitational boost to slingshot it towards the asteroid belt.
3 Arrival at Vesta
16 July 2011 Dawn enters orbit around the large asteroid Vesta, at a distance of 188mn km (117mn mi) from the Sun.
4 Lowest Vesta orbit
8 December 2011 Dawn is moved to its lowest orbit around Vesta, mapping the surface from a height of just 210km (130mi).
Ceres uncovered
9 Dawn stays at Ceres
1 July 2016 The proposal to send Dawn to 145 Adeona was rejected by NASA. Instead, it will continute to study Ceres.
8 End of mission
30 June 2016 Dawn’s primary mission ends and the spacecraft’s scientists put together a proposal for a mission extension.
7 Lowest Ceres orbit
16 December 2015 Dawn reaches its lowest planned orbit around Ceres, descending to around 375km (233mi) above the surface.
Before Dawn’s arrival, there was plenty of speculation that there may be evidence for a hidden subsurface ocean, similar to some of the icy moons of the outer Solar System, like Europa. That hasn’t quite been the case so far, but Dawn did immediately spot something of interest on its approach: a large bright spot on the surface. As it got closer, it became apparent there was not just one bright spot, but hundreds, each much brighter than the surrounding grey surface. This had the public and scientists alike gripped. Theories ranged from ice frozen on the surface to cryovolcanoes, and some even suggested the bright spots were caused by salts left behind by evaporating ice. That latter theory has recently been proven to be correct. Subsurface ice makes its way to the surface, where it sublimates from an ice into a gas, leaving behind any salt that was dissolved in it. Dawn is continuing to orbit Ceres in its lowest planned orbit, 375 kilometres (233 miles) above the surface. The mission has been a huge success, with Dawn providing vast amounts of data that will be pored over for years. Indeed, the mission had been intended to map 80 per cent of Ceres, but more than
99.9 per cent was ultimately mapped. On 30 June 2016, this primary mission (visiting Vesta and Ceres) came to an end. Following this, there was a proposal on the table to send Dawn to an unprecedented third object, a 150-kilometre (93-mile) wide asteroid called 145 Adeona in the asteroid belt. This was possible thanks to its engines still having a significant amount of xenon fuel left, with a planned flyby of the asteroid considered for May 2019. However, at the start of July 2016 NASA decided not to push ahead with this proposal, and instead will keep Dawn in a parking orbit above Ceres. One reason for doing this is that Ceres will soon come closer to the Sun, giving scientists a glimpse at changing surface conditions as the object heats up. Some, though, will no doubt be disappointed that it wasn’t sent on a brand new mission. But even without this third destination, Dawn has been a hugely fruitful mission for NASA. In an age of reusable rockets and space tourism, this multiplanetary spacecraft is another example of how science fiction is very quickly becoming actual science fact.
“After almost nine years in space, Dawn has fired its ion thrusters for more than 5.5 years, setting a new record for powered spacecraft flight” This composite image shows a flow of material inside and outside of a crater called Aelia on Vesta
6 Arrival at Ceres
6 March 2015 Dawn enters orbit around Ceres, the largest object in the asteroid belt, at three times the Earth-Sun distance.
© NASA; JPL-Caltech; UCLA; MPS; DLR; IDA; PSI; LPI; Alamy
5 Departure from Vesta
5 September 2012 After a ten-day delay due to an issue with one of the spacecraft’s reaction wheels, Dawn leaves its orbit of Vesta.
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Deep Space Violent stars, mysterious wormholes and Venus-like exoplanets 92 The hunt for wormholes Astronomers are starting to think that these portals through space-time might be real after all
100 Violent universe The cosmos is full of aggressive offenders
106 Super Venus What can we learn from planets that are bigger, badder and hotter than Earth?
“A single quasar can release as much energy in a second a the Sun can release in 100,000 years”
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Space's destructive objects 90
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Hunting for wormholes
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Evolution of a super-Venus
© ESO; Tobias Roetsch; Shutterstock
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Deep Space
Usually confined to the pages of science fiction, astronomers are starting to think these portals through space-time might be real after all 92
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Deep Space
It was the plot for an epic 2014 Hollywood blockbuster. In Interstellar, a crew of astronauts travel across space on the hunt for an alternative home for humanity. Yet they don’t leave our Solar System by the conventional route; instead, they head into a wormhole in the vicinity of Saturn and emerge almost immediately in a distant galaxy. These wormholes – shortcuts in space and time – have long been a staple of science fiction. But some scientists believe we may soon be able to prove that they are just as real a part of the universe as the Sun and the stars or you and I. The scientific term for this exotic object is an
Einstein-Rosen bridge, which is a clue as to where the idea came from. Wormholes are rooted in Albert Einstein’s general theory of relativity – his groundbreaking masterpiece that turned our ideas about gravity on their head. For centuries we thought we knew how gravity worked thanks to Isaac Newton. Apples fell to the ground and the Earth stayed in orbit around the Sun because of a gravitational pull between the objects. Yet Einstein saw it differently, suggesting that what we experience as gravity is simply a bending of space and time. Under this radical new regime, the Earth orbits the Sun because our star’s mass warps the
“The Earth orbits the Sun because our star's mass warps the space around it, like a bowling ball on a bed sheet”
space around it, much like a bowling ball would warp a bed sheet if it were placed in the centre of it. Our planet is simply following the local curvature of this fabric (which Einstein called ‘space-time’). Such a crazy idea was in dire need of experimental evidence to back it up. Crucially, a solar eclipse in 1919 offered just such an opportunity. When the Moon blocked out the Sun, it was dark enough to see stars close by. Yet we don’t see these stars where they really are because the Sun’s gravity bends their light on the way to us. Newton and Einstein’s competing pictures of gravity predicted different amounts of bending, allowing us to see who was right. It was Einstein who came out on top. So massive objects do indeed bend the space-time around them. This idea is exactly what the fictional astronauts exploited in Interstellar. Imagine space as a sheet of paper. You live at one end and you want to travel to the other end. Ordinarily, you’d have to trudge
What is a wormhole? There's more than one type of shortcut for long journeys across and beyond the observable universe Type 1: Connecting our universe to itself
Type 2: Our universe connects to another
This is the transport mechanism used by the crew of astronauts in the film Interstellar as a shortcut between our Solar System and a distant galaxy. Einstein’s general theory of relativity suggests it might be possible to bend space-time sufficiently to bring you and your destination much closer together.
The equations of Einstein’s general theory of relativity blow up in a fever of infinities at the bottom of a black hole. Replacing them with a slightly modified set of rules suggests that a wormhole to another universe might exist in its place. But we do not have the evidence yet that those alternative rules are the right ones to use.
Mouth All wormholes have two openings, often called ‘mouths’ – you enter one and exit the other.
Throat The tunnel that connects the two mouths is known as the ‘throat’, but it’s hard to keep it open.
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Ordinary space The ‘flat’ areas that lie far away from the mouths are known as ordinary space.
One mouth per universe This time the entry mouth is in a different universe to the exit mouth.
Journey to the multiverse Rather than connecting two points in the same universe, the throat is a portal to a parallel universe.
The hunt for wormholes
the entire length of the page to get there. But what if you folded the paper in half instead? Suddenly, where you are and where you want to be are right next to each other. You simply have to jump that tiny gap. We call these objects wormholes because it is like a worm trying to navigate its way around an apple. To get from the top to the bottom it has two choices: crawl around the outside or chew a shortcut through the middle. Until recently, our chances of finding these objects (if they do indeed exist) were slim at best. But that changed in February this year when the scientists behind the LIGO experiment, based in the US, announced the first ever detection of gravitational waves. These are tiny ripples in the fabric of space-time, predicted by general relativity, and which spread out through the universe much like ripples on a pond. “It was a game-changer,” says Vitor Cardoso, a physicist at the University of Lisbon in Portugal. Two black holes – each about 30 times
“With this new set of rules, it would be possible for an observer to go through a wormhole and cross over to another region of the universe”
Have your say… Do you think wormholes could exist? Yes 84%
No 16%
Diego Rubiera-Garcia The Laser Interferometer GravitationalWave Observatory (LIGO) at Livingston, Louisiana, listens for faint whispers of the most energetic events in the universe
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Deep Space
How wormholes are made If these space-time tunnels do exist, what would they look like and how would they come into existence?
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Collapse of the core
Black hole
When a gigantic star – with a mass much more than 20 times the mass of the Sun – dies, sometimes a black hole is formed. When we refer to a star dying, we mean that it no longer has any nuclear fuel to burn and this means that gravity is unable to override an outward force. The core has no choice but to collapse in on itself in the catastrophic explosion of a supernova. The devastated star’s outer layers are expelled into space while the core continues to shrink in size.
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A cosmic plughole
Shrinking smaller and smaller, the core continues to pale in significance compared to its former stellar glory, collapsing into an even smaller size. However, while it has shrunk to a speck, all of its mass is concentrated in a very small area. Meet what is known as a singularity, which might be small, but it is so heavy that it has the ability to really bend space-time. Not even light can escape the gravitational pull of the singularity. Gravity is essentially the effect that a heavy object has in the fabric of space-time that can be found around it. Picture a sheet held loosely at each of its four corners. If you place a heavy object onto that sheet, you’ll find that it makes a dent. Anything in the vicinity of the object that made the dent will fall towards it. This is gravity.
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Space-time tunnel Singularity
Doughnut singularity Black hole Everything – from matter to light – is pulled into the high gravity black hole. Confusingly, this is the future end of the wormhole.
The makings of a doughnut
A star’s core can still be found to be spinning when it decides to collapse. Crumbling to the minuscule, yet hefty, singularity, it begins to rotate faster and faster. It spins so quickly that what’s left of the star’s material spreads out and is moulded into a doughnut. Space-time is no longer focused on a single point; it’s now being wrapped around this space ring, creating a tunnel.
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Punching through space
The tunnel being made punches its way through the fabric of space-time and, almost in a state of reversal, it emerges backwards in time and into the past. This tunnel, which could feasibly work its way into another parallel universe, is called an Einstein-Rosen bridge, or a wormhole. Any matter that is grabbed by the black hole is passed through this tunnel.
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Meet the white hole
If you were to travel through a wormhole, you would reach its far side, which can be likened to a black hole in reverse: the white hole. Matter pulled in by the black hole will emerge from the singularity found at the white hole’s centre and be released back into space. Just as nothing can escape a black hole, it’s not possible to enter a white hole.
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White hole Matter and light is thrown out into the past, very much like a smaller version of the Big Bang.
Einstein-Rosen bridge or wormhole
The hunt for wormholes
more massive than the Sun – had rammed into each other 1.3 billion years ago. Their violent marriage sent a tsunami of gravitational waves roaring out through space-time, eventually reaching the LIGO instrument in September 2015. Cardoso’s research suggests that two colliding wormholes would produce a similar burst of gravitational waves. Excitingly, however, he says the resulting waves would be slightly different, allowing us to distinguish between black holes and wormholes. The key here is what’s known as the ‘ringdown’ – the way in which the gravitational waves die away after the initial collision. It’s similar to the way the sound of a ringing bell fades over time. “With two colliding wormholes you would see the ringdown – just like you see for black holes – but if your detector is very sensitive then seconds, or tens of seconds, after the main burst you would see something different,” he says. This is due to the
nature of black holes – gravitational behemoths that swallow anything that gets too close. The ringdown of colliding black holes always gets quieter, quickly fading away to silence. But with colliding wormholes, after the silence you get an echo – a sudden, late signal as the gravitational waves bounce off the wormholes’ surface. You can’t get that with black holes as they swallow everything. Unfortunately, LIGO currently isn’t sensitive enough to pick up these late changes. But researchers are upgrading LIGO’s instruments and it could be possible in “ten years from now or so,” Cardoso says. The other exciting project on the horizon is the European Space Agency’s (ESA’s) Evolved Laser Interferometer Space Antenna (eLISA). It is a gravitational wave observatory in space that has a tentative launch date of 2034. However, in 2015 ESA launched LISA Pathfinder – a test mission to develop certain key technologies that are vital
“Two colliding wormholes would produce an echo through space that would be detectable with the next generation of experiments”
Where scientists think wormholes exist If they are out there, astronomers think that they know where these portals through space-time could be hiding
Centre of the Milky Way Last year Italian researchers suggested there could be a wormhole lurking in the centre of the Milky Way some 27,000 light years away. Ordinarily, a wormhole would need some exotic matter to keep it open, but researchers believe dark matter might be doing the job instead.
Inside a black hole Rather than having a singularity at the centre as general relativity predicts, some researchers believe we’d find a wormhole – one that could allow us to make the journey from Interstellar a reality. However, the jury is out on whether it would be big enough for a human to traverse.
Quantum foam
ESA’s Evolved Laser Interferometer Space Antenna (eLISA), due to launch in 2034, is a gravitational wave observatory that will continue the search for wormholes
Physicists think that even empty space isn’t truly empty – on the smallest scales it is a cauldron of bubbling energy popping in and out of existence. As such, some think that fleeting, virtual black holes may be being created all the time in this ‘quantum foam’. We’d need to put a lot of energy in if we wanted to make one permanent.
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Deep Space
A technician at the LIGO experiment, which announced it had detected gravitational waves for the first time earlier this year
for eLISA’s success. And in April this year ESA announced that LISA Pathfinder had indeed shown that eLISA was feasible. But ringdowns of collisions might not be the only route to finding a wormhole. Cardoso’s colleague at the University of Lisbon – Diego Rubiera-Garcia – has another idea. He’s been studying what goes on deep inside a black hole. The conventional picture of black holes, as described by general relativity, has all the in-falling mass squeezed down into an infinitely small, infinitely dense point – a singularity. “Any observer who approaches this point is destroyed,” says Rubiera-Garcia. “After that you will disappear from space-time, there is nowhere else for you to go.” It is at this singularity that general relativity breaks down, where its equations stop making sense. This leaves many physicists confident that we need a new set of rules to replace general relativity in such an extreme environment. And that’s where wormholes come in. When Rubiera-Garcia applied one of the alternative sets of rules to the physics of black holes, the singularity disappeared and the mathematics yielded a wormhole in its place. “Then it would be possible for an observer to go through this wormhole and cross to another region of the universe,” he says. The trouble is that this shortcut through the cosmos might just be a phantom of the mathematics: the alternative to general relativity that Rubiera-Garcia
How do we know if we’ve found a wormhole? There are several clues to look out for if we find a candidate for a space-time portal
Gravitational wave ringdown echo
Microlensing
Heading into one
The gravitational waves from colliding black holes die away very quickly. But two colliding wormholes would produce an echo detectable with the next generation of experiments.
If a wormhole passed in front of a distant star it would bend the star’s light slightly in an event called ‘microlensing’. The technique has already been used to find rogue planets.
Some scientists believe that black holes are actually wormholes in disguise. It’s a risky endeavour but sending something into one would let us know for certain if wormholes really do exist.
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The hunt for wormholes
used to find it might not be how our universe really works. So, as with all good scientific theories, it needs to be tested, just as Einstein’s was in 1919. That’s where gravitational waves come back in. Once we have built up a significant library of gravitational wave detections, we can trawl through the data looking for departures from what general relativity predicts we should see. If these departures are found, and they match what the alternative theory predicts, it could signify that wormholes do indeed lurk inside black holes. So the first detection of gravitational waves has ushered in a new era of scientific investigation, one in which we may well find out that wormholes aren’t just science fiction after all.
“To even create a wormhole requires exotic matter that we have never seen here on Earth”
If they exist, could we travel through a wormhole? YES NO
Vitor Cardoso University of Lisbon, Portugal “The possibility of using wormholes to travel is not completely excluded, at a theoretical level. However, to even create a wormhole requires exotic matter that we have never seen here on Earth.”
Diego Rubiera-Garcia University of Lisbon, Portugal “The problem is that usually these wormholes are very small, and when I say small, I mean really, really small. So it is not possible for a real observer to pass through that wormhole.”
Vitor Cardoso
© Shutterstock; Caltech; MIT; LIGO Laboratory; ESO; B. Tafreshi; NASA; ESA; D. Coe; G. Bacon; CXC; M.Weiss; CQGplus; Les Bossinas
Einstein’s general theory of relativity suggests that what we experience as gravity is simply a bending of space and time
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Deep Space
ENTER THE COSMIC BATTLEFIELD
VIOLENT UNIVERSE The cosmos is not the serene place it first appears – it is full of aggressive offenders
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Top 5 most destructive objects Gamma ray bursts Caused either when a massive star collapses into a black hole or when two neutron stars collide, the total gamma ray energy emitted is 100 trillion trillion times more than the largest nuclear weapon ever tested on Earth.
Supernovae An explosion, which occurs upon the death of a star, supernovae are at least eight times more massive than our Sun. A supernova can commonly release twice the amount of energy as a typical gamma ray burst.
Hypernovae Some supernovae can be particularly brutal. Known as hypernovae, these events are associated with the origin of long gamma ray bursts. The total amount of energy released can be 100times greater than an ordinary supernova.
Quasars The most energetic form of Active Galactic Nuclei (AGN), a single quasar can release as much energy in a second as the Sun can release in 100,000 years. They can even be 100 times as luminous as an entire galaxy.
Magnetars A particularly vicious form of neutron star, the strength of a magnetar’s magnetic field is a billion times stronger than any magnet created by scientists on Earth. Such a setup fires high energy X-rays and gamma rays into space for 10,000 years.
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As ultraviolet radiation cascades down from space, Earth’s place as a life-friendly planet is under threat. The surface of our world is bathed in this high-energy radiation and it penetrates our oceans to depths of 75 metres (246 feet). The damage is catastrophic. The intense glare fries ocean plankton and those organisms which survive divert all their energy to repairing their DNA rather than photosynthesising. Oxygen levels drop as carbon dioxide levels rise. The knockout blow for many larger species comes as dwindling plankton numbers offer scant food resources, with the effect rocketing up the food chain. Thankfully this fictional future is very unlikely, but what would have caused such devastation? The answer is a gamma ray burst (GRB). They often emit as much energy in a few seconds as our entire galaxy
does in a year. If such a volley of gamma rays were to strike our planet, it would rip molecules in our atmosphere apart, releasing an army of ultraviolet photons to devastate the world’s biosphere. Luckily, these events are rare, particularly in our own Milky Way. In fact, we’ve never observed one in our galaxy. Even if one were to go off, it would have to be aligned almost perfectly with Earth. However, studying them reveals just how violent our universe can be. As the majority of GRBs observed by astronomers are in distant galaxies, working out exactly what causes them is notoriously tricky. However, most researchers agree that they are related to the death of stars. When a star at least eight-times bigger than the Sun begins to die, it alters the way it fuels itself. During the main chunk of its lifetime it was
“A gamma ray burst often emits as much energy in a few seconds as our entire galaxy does in a year”
At the heart of a monstrous magnet
converting hydrogen into helium via nuclear fusion. However, it now starts to fuse helium into carbon and begins to bloat outwards. The core continues to fuse heavier and heavier elements until it creates a dense, iron core. The core then collapses under its own weight, before rebounding and sending a shockwave through the star’s outer layers, causing it to explode as a Type II supernova – an event so energetic it can outshine all the stars in a galaxy and be seen even during daylight hours. GRBs are associated with a particularly vicious form of supernova, known as a hypernova, which can be up to 50 times more energetic than the ordinary variety. They are thought to form when the iron core of a star at least 30 times more massive than the Sun collapses to form a black hole. Twin jets of energetic radiation surge away from the region close to the black hole and the gamma rays are believed to be produced by collisions between the jets and the outer layers of the star. At least that is the favoured origin mechanism for around 70 per cent of observed GRBs, those that last longer than two seconds. These are known as
Magnetic field Magnetars are known for their extremely powerful magnetic fields, which produce high-energy X-ray and gamma ray bursts. These magnetic fields are hundreds of millions times stronger than any manmade magnet on Earth.
Outburst The fireball, produced by magnetic field decay, ejects intense flashes of high-energy electromagnetic radiation. These giant flares leave the surface of the magnetar at the speed of light and their radiation has even been recorded on Earth.
Solid crust This outer layer is often only 500m (1,640ft) thick. Eventually, it fractures under the extreme magnetic stress. After all, a magnetar placed at the distance of the Moon could wipe all the credit cards on Earth. X-rays are then released by the resulting fireball.
The fluid layer Extending out from the core over a distance of approximately 6km (3.7mi), this heavy fluid interior is mostly made of neutrons with a scattering of other atomic particles. Here, the process of convection carries heat away from the core.
The solid core Measuring just 3km (1.8mi) across, the central core of a magnetar is made of subatomic particles called quarks – the same building blocks from which protons and neutrons are constructed.
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Violent universe
“long gamma ray bursts”. However, roughly 30 per cent of GRBs are much shorter, typically lasting just 0.2 seconds. Rather than the collapse of a single star, these short gamma ray bursts are believed to originate from the collision of two neutron stars – the remnants of dead stars smaller than those which form black holes. The size of a city, a neutron star is so dense that a teaspoon full of its material weighs more than a mountain range and their magnetic fields can be a trillion times stronger than our Sun’s. Computer simulations show that when two neutron stars spiral inwards towards each other they merge to form a black hole. The magnetic fields merge, too, and the overall strength of magnetism is boosted by a thousand times. Eventually, the new black hole’s magnetic field aligns into jets, which can power a short GRB. Not content with being responsible for these mighty events, neutron stars are also thought to be behind another of the universe’s rogues gallery of violent offenders: magnetars. Souped-up versions of single neutron stars, they boast a significantly stronger magnetic field. It is estimated that ten per cent of neutron stars end up as this enhanced variety. With a rotational period of at least one second, they also spin more slowly than their traditional counterparts, which can rotate dozens of times in the same period. Their stronger magnetic field can yield intense flashes of gamma rays and X-rays, but not for long – the typical lifetime of a magnetar is just 10,000 years. A blink of an eye in astronomical terms. And, there are thought to be at least 30 million extinct magnetars in our Milky Way galaxy alone. Sticking with the merging remnants of dead stars, there is another type of supernova, which is sometimes the result of two white dwarfs colliding together. Less massive than neutron stars or black holes, white dwarfs are the leftovers from stars about the size of the Sun. If two Sun-like stars were orbiting around each other in a binary system, when they both die the resulting white dwarfs can collide with each other. However, there is a limit to how massive a single white dwarf can be – known as the Chandrasekhar limit – and a wave of nuclear fusion will rip apart any white dwarf that ventures too close to it. The resulting Type 1a supernova releases 200 million billion times more energy than the Sun provides to the Earth in an entire year. Again, enough to briefly outshine the galaxy it resides in. Analysing these explosions in relatively nearby galaxies has allowed astronomers to measure the rate at which the universe has expanded in the past. However, if we are searching for the universe’s most violent objects then we have to travel far away from the local universe to the very furthest reaches of the cosmos, where we find quasars. They are the brightest objects in the universe, form part of a group of objects astronomers refer to as Active Galactic Nuclei (AGN) and get their name from the contraction of “quasi-stellar”. The luminosity of a single quasar can be up to 100,000-times greater than our entire Milky Way galaxy. They represent the highly energetic cores of some of the earliest, and therefore most distant, galaxies in the universe. The secret of their power lies in a very similar mechanism to that of GRBs but on a much larger scale. It is thought that large galaxies form when
Pint-sized danger: neutron stars Tiny but mighty The catastrophic collapse of a star into a neutron star squashes both matter and magnetic field into a space about the size of a city. Despite this diminutive size, a neutron star weighs more than the Sun.
She’s electric
Radio lighthouse
Rotating many times a second, the electric field generated by a neutron star is 30-million-times greater than a lightning bolt. We’re talking about a voltage measured in petavolts, which is a quadrillion volts!
The magnetic field generates beams of energy at the neutron star’s poles. Like a lighthouse, these beams rotate with the neutron star and we can hear them as pulses of radiation with our radio telescopes, hence why they are sometimes called pulsars.
Mighty magnetism The magnetic field of a typical neutron star can be one-million-times stronger than Earth’s own magnetism. Magnetars, on the other hand, can have magnetic field strengths over a trillion times more than Earth's.
X-ray source If a neutron star starts to suck in material from the surrounding region then it becomes a very powerful source of X-rays – one of the strongest in our galaxy. There are thought to be 100 million neutron stars in our Milky Way.
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much smaller galaxies merge together. If each small galaxy had a reasonably big black hole at its centre then they will combine in the newly created galaxy to form a supermassive black hole with a mass greater than a billion Suns. As this new behemoth starts to devour the surrounding material, the magnetic field around the black hole eventually sprouts two distinct jets of radiation, shooting out from the compact galactic centre like a lighthouse beam. The angle at which we observe this beam determines what we call it. If we see the beam at an angle then that’s a quasar. Look straight into the beam and you have yourself a blazar. Finally, if you're looking at right angles to the beam
astronomers know it as a radio galaxy. The study of AGNs is still a relatively new area of astronomy, with observations by the Hubble Space Telescope sending what we knew about them sky-rocketing. Yet one of the biggest mysteries surrounding them is why the nucleus of the Milky Way isn’t currently anywhere near as active as some of these more distant galaxies. After all, observations suggest our galaxy is centred around a supermassive black hole with a mass equivalent to 4 million Suns. There is some evidence, however, that the Milky Way hasn’t always been so serene. In 2010, the team behind the Fermi Gamma Ray Space Telescope announced the discovery of the so-called Fermi
“Giant gamma ray structures were discovered extending for 30,000 light years either side of the galactic centre”
bubbles – giant gamma ray structures extending for 30,000 light years on each side of the galactic centre. Their presence points towards a sizeable and rapid eruption of energy close to the Milky Way’s black hole several million years ago. In this eruption, gas and other material was driven out at millions of kilometres, or miles, per hour. Two explanations are currently on offer for these remarkable structures. The first is that the area close to the galactic centre underwent a period of unprecedented star formation, with many of the stars exploding together as supernovae almost simultaneously. The other is that around the same time our supermassive black hole woke up and, starved from its hibernation, went on a feeding frenzy. If it turns out to be the latter, we should be thankful that our black hole effectively goes to sleep for extended periods of time. A healthier appetite would likely flood the Milky Way with intense bursts of lethal radiation and the rest of the violent universe would be the least of our problems.
Despite their distance from us, space telescopes can see quasars thanks to their luminosity
The gamma ray bubbles discovered by the Fermi telescope emanating from the centre of the Milky Way
This gamma ray burst was discovered in a distant galaxy by Hubble in 2013
As material spirals into a black hole, jets of high-energy radiation are often produced
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A giant jet of radiation extending out from the active centre of the galaxy M87
Violent universe
Keeping vigil over violence Studying it further The Ultraviolet/Optical telescope onboard the satellite is also pointing in the same direction as the X-ray Telescope. It can pick up some of the other forms of light created during the GRB.
Pinning it down Within a minute of BAT being triggered, SWIFT’s X-ray Telescope (XRT) will have worked out the precise location of the Gamma Ray Burst to within a few thousands of a degree.
Spotting the burst
A bright burst A GRB is formed when jets from a black hole interact with surrounding gas to produce a cascade of electromagnetic radiation. While this includes visible light and X-rays, many high-energy gamma rays are also created.
Ground observation
The SWIFT telescope views half of the sky every time it orbits the Earth and its Burst Alert Telescope (BAT) is always on the lookout for sudden intense flashes. When it spots one, it immediately sends a message to astronomers on Earth and automatically orientates itself for a closer look.
While SWIFT keeps an eye out for GRBs from orbit, a number of Earth-based telescopes are also searching for electromagnetic radiation from the ground, such as the Major Atmospheric Gamma Imaging Cherenkov Telescopes (MAGIC). Its huge 17m (56ft) wide reflecting surface is much larger than any telescope currently in orbit.
Afterglow
Black hole Energy from the matter that falls into a black hole is focussed into powerful jets at its poles.
Emission The jets fire out material at close to the speed of light. Shockwaves within the jets give off gamma rays.
Another shockwave occurs as the jets collide with the interstellar medium, producing different wavelengths of radiation.
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© Tobias Roetsch; Nicholas Forder; Adrian Mann; ESO; NASA; ESA; Hubble; Dana Berry
How gamma ray bursts are made
Deep Space
What can we learn from the planets that are bigger, badder and hotter than Earth?
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As we continue to find more and more planets outside of the Solar System, one thing is becoming very obvious: there are a vast array of planets, of all sizes and orbits. We’ve found super-Earths, rocky planets bigger than Earth in habitable orbits, and hot Jupiters, gas giants in tight orbits. And now a new class of planet is coming to the fore: the super-Venus. Finding out exactly how common the array of planets in our Solar System might be has been one of the key questions for planet hunters so far. We have four relatively Earth-sized terrestrial planets, and four gas giants. But our closest planet to the Sun is Mercury, which orbits the Sun at about a third of the distance that Earth does. That, as it turns out, seems rather unusual. We are finding that many planetary systems have worlds in very tight orbits, a
fraction of Mercury’s, with years lasting just a matter of days. These worlds are extremely hot, owing to their proximity to their star, and almost certainly uninhabitable to any life as we know it. Most of the worlds discovered so far have either been Earthsized, or as big as gas giants like Jupiter. But that all changed in 2013 with the discovery of the first superEarth in such a close orbit – suggesting the world was not really a super-Earth, but a super-Venus. As the name suggests, these are large worlds – bigger than Earth, up to around twice the size – with atmospheric conditions that resemble the hottest planet in our Solar System, rather than the only one we know to have life. Owing to the size and the gravity of the planet, they are able to support huge atmospheres that can trap a large amount of heat. It
“Its proximity to Earth makes Gliese 1132b the most important planet ever found outside of the Solar System” Dr Drake Deming
is possible they went through runaway greenhouse effects similar to Venus in our Solar System, but on an extreme scale. “The distinction between a super-Venus or a superEarth signifies the location of the planet relative to its host star, and thus a measure of the expected temperature of the planet,” Charles Beichman, executive director of NASA’s Exoplanet Science Institute, tells All About Space. “Venus, being closer to our Sun than Earth, receives much more energy than Earth and thus has a hotter temperature, an effect added to by the extreme runaway greenhouse effect from Venus’ thick atmosphere.” One such example is Gliese 1132b, which orbits its host star in a mere 1.6 days. Its relative proximity to Earth of 39 light years, though, led University of Maryland astrophysicist Drake Deming to say it was “arguably the most important planet ever found outside of the Solar System”. The planet has an estimated average temperature of 230 degrees Celsius (440 degrees Fahrenheit), and is thought to be tidally locked – with one hemisphere always facing the Sun. At 1.2 times the size and 1.6 times the mass of Earth,
Evolution of a super-Venus Size matters The size of a super-Venus, 1.5 to 2 Earth radii, would allow it to retain a thick atmosphere without losing it due to evaporation or the solar wind from its host star. In fact, compared to Venus, these larger planets could very likely have much thicker atmospheres, perhaps thicker than all known terrestrial planets.
Habitable location Super-Venus exoplanets are largely thought to be located inside the habitable zone of stars. They may have once been able to host liquid water, perhaps when their host star was less active. Venus, in our own Solar System, is thought to have hosted water before the planet started to get much hotter.
Turning up the heat As the super-Venus got hotter, any water that was on its surface would have begun to evaporate. This would have thickened the atmosphere, in turn causing the planet to get even hotter, increasing the temperature and rate of evaporation. This is known as the runaway greenhouse effect.
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Dry as a bone? Ultimately, these processes would likely leave a super-Venus barren and inhospitable to life as we know it, like Venus. But some, located just at the edge of their star’s habitable zone, may have extreme seasons on their surface that support liquid water. Again though, their potential for habitability is questionable.
Super Venus
Working out the weather We will soon be able to study the atmospheres of some nearby Venus-like exoplanets
What is it made of? The atmosphere’s composition also affects the light, letting us study its absorption and allowing us to characterise the exoplanet.
Composition
Atmospheric absorption
The composition and thickness of the atmosphere will dictate what sort of light we receive on Earth.
Some of the star’s light will travel through the planet’s atmosphere, if there is one.
Planetary transit As a planet passes in front of its star relative, as viewed from Earth, it blocks the star’s light.
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How thick is it? A thick atmosphere will block more light and push it to the red end of the spectrum, while a thin atmosphere will show light on the blue end of the spectrum.
Worlds close to their host star can be extremely hot
Brightness
The thickness of a planet’s atmosphere can be identified during its ‘transit’ across the face of its parent star
Time in hours
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“Venus may have had liquid water on its surface 4 billion years ago when the Sun emitted 25 per cent less light” The Kepler Space Telescope has found the majority of exoplanets we know of today
Planets have been found around red dwarfs, stars dimmer than our Sun
Planetary systems form with worlds possessing various characteristics
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any atmosphere it retains is likely to be thick, giving it this high temperature. But its proximity could allow it to be studied in greater detail to learn more about these super-Venus worlds. Planets in tight orbits like this allow us to make frequent observations as they transit their star relative to Earth. This isn’t the only way super-Venus exoplanets can form though. Scientists believe that large terrestrial worlds located just within their star’s habitable zone can also evolve to have extreme temperatures. While these worlds wouldn’t receive a huge amount of sunlight, their thick atmospheres would trap any heat that came their way, roasting their surface and mimicking conditions on Venus in our Solar System. One such world that has been discovered, Gliese 832c, orbits its host red dwarf star every 36 days. Located just 16 light years from Earth, it is a prime candidate for further study. As red dwarfs are considerably dimmer than our Sun, it receives a similar amount of sunlight to Earth, but with a radius 1.6 times that of Earth and a mass five-times greater, it has almost certainly accumulated a huge atmosphere over time, causing it to trap a large amount of heat. Another super-Venus, named Kepler 69c, was discovered and announced by NASA in 2013. At 1.7 times the size of Earth and orbiting just within its star’s habitable zone, it could possibly have similar conditions to Gliese 832c. Originally, some had speculated this world would be Earth-like, with liquid water on the surface. Now, we’re fairly certain it’s more like a super-Venus. Perhaps this world more than any other, though, shows the ambiguity between worlds like our own and worlds like Venus. We don’t fully understand what causes a planet to go one-way or the other and studying planets like this in more depth could provide the answer. In our own Solar System, it’s thought that Venus may have had liquid water on its surface about 4 billion years ago, during the Archean Eon, when the Sun emitted up to 25 per cent less light for reasons that are poorly understood. But when the Sun started to reach its current level of activity, it warmed the surface of Venus and evaporated some of the water in the oceans, causing the atmosphere to get thicker and, in turn, heat the planet further. The result was a runaway greenhouse effect, leading to the extremely hot and barren world we see today, which retains an extremely thick atmosphere. The super-Venus is a relatively new class of exoplanet, so there is still a lot we do not know about them. But there is one thing we can make a good guess at, and that is the size of their atmosphere. Larger than Earth, but having gone through the same or similar processes to Venus, they could likely support vast atmospheres thicker than anything we have seen on any terrestrial planets and feature extremely high surface temperatures. For example, super-Venus Gliese 1132b boasts an estimated surface temperature of 230 degrees Celsius (440 degrees Fahrenheit). But a planet that is too hot, for example several thousands of degrees, is not thought to be able to hold onto an atmosphere for long. Our methods of studying super-Venus planets are limited at the moment, but in the coming years a new array of telescopes on the ground and in space – including the James Webb Space Telescope – will
Super Venus
Super-Venus candidates
Kepler 69c
Gliese 1132b
Gliese 832c
Parent star: Kepler 69 Distance (in light years): 1,930 Size (in Earths): 1.7 Estimate temperature: Unknown Discovered by: Kepler Space Telescope
Parent star: Gliese 1132 Distance (in light years): 39 Size (in Earths): 1.16 Estimate temperature: 230°C (440°F) Discovered by: MEarth-South array
Parent star: Gliese 832 Distance (in light years): 16 Size (in Earths): Unknown (But mass is 5.4 Earths) Estimate temperature: Unknown Discovered by: Anglo-Australian Telescope, Magellan Telescope, European Southern Observatory
Inside the Goldilocks zone Kepler-69 system Some super-Venus planets like Kepler 69c reside just inside their star’s habitable zone 69c
69b
Habitable zone Mercury
Venus
Earth
Mars
Solar System Venus, Earth and Mars are all within the habitable zone of our Sun
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How Venus’ past could become Earth’s future Could our planet turn equally barren and inhospitable?
Runaway greenhouse effect Earth would have to warm up considerably to experience a runaway greenhouse effect.
Atmospheric thickness Venus’ atmosphere is 96.5 per cent carbon dioxide, while Earth’s is 400 parts per million but rising, in part, due to human activity.
Trapped heat If the atmosphere gets too thick, it will trap too much heat and cause the runaway greenhouse effect.
Solar activity If humans do not begin the process, then increased solar activity in a few billion years will surely do the trick.
Human activity Some have predicted that human activity and the burning of fossil fuels could begin the runaway greenhouse process.
be able to characterise the atmospheres of some of these worlds. They will do this by observing the light coming through their atmospheres, a process known as transmission spectroscopy, to ascertain both the presence of an atmosphere and its thickness, and perhaps even its composition. Inevitably, the question will fall on habitability. Could these worlds support life? The answer is complicated. For super-Venus exoplanets in tight orbits around their host star, it’s extremely unlikely. Orbiting in a matter of days, they could be subjected to heat that would cause even rocks to sublimate (evaporate). Perhaps only if they were tidally locked – with one side of the planet always facing the star – could their exist a small region where life could exist between the scorching hot nearside and colder farside, but this is currently pure conjecture. For those worlds found just inside the habitable zone, it’s a bit more unclear. The energy from their host star will likely have evaporated any liquid water they once had long ago. Even if they receive a similar amount of sunlight to Earth, the expected thick atmosphere of these large worlds would raise the heat to an inhospitable level. But that atmosphere might also be a saving grace. We know that atmospheres cause weather systems – we see it on Saturn’s moon Titan, Jupiter and, of course, Earth. Could a super-Venus also have a weather system, one that circulated heat around the planet? “We know little about the exact parameters which determine the precise boundaries of a habitable zone, so in the case of Gliese 832c, which is right at the inner habitable zone boundary and even moves in and out of the inner edge with its slightly eccentric orbit, it is impossible to make categorical statements,” says Beichman. Perhaps importantly, in some extreme scenarios they may also be snapshots into what will become of Earth. As our atmosphere gets thicker, and more heat is trapped on our planet, we edge ever closer to undergoing our own runaway greenhouse effect. When this will happen is up for debate. Human activity has raised the amount of carbon dioxide to 400 million parts per million in our atmosphere. This is not much compared to the Venusian atmosphere, which is 96.5 per cent carbon dioxide, but there’s little doubt our planet is warming up. Could it ever pass a point of no return? It almost certainly will in a few billion years, when our Sun’s activity is expected to increase and subject our planet to more heat. Some super-Venus exoplanets, particularly those located at the inner edge of their habitable zones, appear to have gone through something similar. Our planet
“We know little about the exact parameters which determine the precise boundaries of a habitable zone” Dr Charles Beichman
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Super Venus
Will Earth one day experience its own runaway greenhouse effect?
“Data from Kepler suggests that 15 to 25 per cent of all small stars host planets in or around the habitable zone” Venus today is dry and barren, but it may once have had water on its surface
© Tobias Roetsch; NASA; Ames: JPL-Caltech
may ultimately go the same way, with little chance of retaining liquid water. So, studying super-Venuses could provide more detail on what will happen. Scientists will be keen to work out the composition of these atmospheres, if possible, and see if there are any indications that they once had liquid water on their surface. Venus, for example, has large amounts of water vapour in its atmosphere – an indicator that it once had liquid water on the surface. And it’s not like we will be short of planets to look at. While we know of only a handful of super-Venus exoplanets so far, there are hundreds of billions of planets in our galaxy – and several thousand are close enough for direct observations with current technologies. “Data from the Kepler spacecraft suggests that up to 15 to 25 per cent of all small stars, such as Gliese 832, host planets in the Earth or Venus range and located in or around the habitable zone of the host star,” says Beichman. “We know less about the planetary census for stars more like our Sun, but the preliminary statistics suggest fractions like 5 to 15 per cent for Earth-sized planets in the habitable zone.” Most of the recent focus in planet hunting has been on finding an Earth twin, and we are pretty close with worlds like Kepler 452b. But perhaps it is these super-Venus worlds that will prove to be of more interest in the near future. Those that orbit close to their stars, and are within 100 light years of Earth, will give us a fascinating opportunity to study atmospheres beyond our Solar System. This is an area of astronomy we are only just delving into – and scientists are keen to see what they will find. “In the more distant future, we will launch space telescopes capable of imaging Earth-sized planets directly in the habitable zones of their host stars, and use spectroscopy to look for signatures of life, such as oxygen and ozone,” says Beichman. Until then, we can use these super-Venus alien worlds as a testing ground, and in the process learn more about a type of terrestrial planet that is hugely exciting in its own right.
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Space Science The nuts and bolts behind our knowledge of how the universe works 116 10 amazing Space Station experiments The International Space Station is a huge orbiting research laboratory
124 Why we live in a multiverse Could our entire universe be just one small part of many? The evidence is mounting up...
134 What happened before the Big Bang? What happened before the birth of the universe?
144 Dark energy It's the most mystifying phenomenon in the universe, but we're hot on its trail
“Just this year, scientists discovered that the universe is expanding faster than we originally thought”
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Investigating multiple universes
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Experiments in zero gravity
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© Shutterstock; Tobias Roetsch; NASA
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Robonaut
Space gym
The International Space Station is more than just an outpost in space, it is a huge orbiting research laboratory The International Space Station (ISS) houses an incredible array of cutting-edge research facilities, allowing scientists back on Earth to conduct pioneering experiments in space. Different space agencies, academic institutions and private companies from across the world share the onboard facilities, taking it in turns to perform their experiments. Delicate tests can be conducted in microgravity inside the station itself, and outside experiments can be exposed to vacuum and radiation. With a clear view of space and out of the reaches of the Earth’s atmosphere, the ISS is also the perfect place to investigate the universe.
3D printing in microgravity
Some experiments investigate the physical sciences, looking at the behaviour of different materials in space, while others focus on biology, helping us to understand how the human body is affected by space travel, or how to grow food away from Earth. Others monitor Earth, taking advantage of the ISS’s incredible view of our planet below. The station also houses sophisticated equipment to examine space itself and inside, advanced technology can be developed and tested in microgravity. Join us as we investigate ten awesome International Space Station experiments, from robotic crew members to an orbiting coffee machine.
Tomatosphere
Remote-control space
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Working with a humanoid
The ISS is always occupied by at least three human crew members and, since February 2011, they have been joined by the Robonaut 2. On its arrival, the robotic crew member met the Space Station commander with a handshake and greeted the public by signing ‘hello world’. This incredible robot is the result of a collaboration between NASA, General Motors, and Oceaneering Space Systems. Together, they wanted to create a robot that was capable of carrying out repetitive, uncomfortable or dangerous tasks. Robonaut 2’s hands are flexible like our own – its thumb can bend to touch all of its fingers – and it has a grip strength equivalent to a human. Its arms are soft and padded and contain springs that give way easily when pushed, allowing astronauts to work safely alongside. The robot has infrared cameras for depth perception and an additional four visible light cameras, which help it to ‘see’ in stereo. And, since 2014, it also has a pair of flexible legs, each fitted with an ‘end effector’ where the foot should be, allowing it to move freely around the station. With a little more upgrading, the team hope that this robotic crewmate will eventually be able to work on the outside of the Space Station.
Opposable thumbs Robonaut 2 has flexible hands, and it can easily touch its little finger to its thumb.
Human-like senses Robonaut has over 350 sensors, including five cameras in its helmet.
Padded metal Robonaut is made from aluminium and steel, but is coated in soft protective padding.
Robonaut's brain The 38 processors responsible for controlling Robonaut are housed inside its torso.
Interchangeable lower body Robonaut's body can be attached to wheels, legs, and even a robotic arm
Biped legs (in development)
Segway
Robotic arm
Four-wheeled chassis
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10 amazing space station experiments
The squids are housed in tubes of seawater
2 Squid behaviour in microgravity The final flight of NASA’s Space Shuttle program carried some unusual passengers to the space station: three Hawaiian bobtail squid. These little sea creatures are usually found hiding in the sand on the shallow seabeds surrounding Hawaii, and at only five centimetres (two inches) long, they are the perfect size for experiments inside the ISS. This particular species was chosen because of its close relationship with another organism. Hawaiian bobtail squid naturally share their bodies with a species of bacteria called Vibrio fischeri. These bioluminescent microbes light the squid's silhouette, helping to keep it camouflaged in the dappled light of the water.
The squid only live for around ten months, but these intrepid explorers made the journey into space to help researchers understand how bacteria that live inside animals are affected by microgravity. Beneficial microbes inside the human body help to protect us from infection, so these kinds of experiments are going to be really important for astronaut health on long-term missions. With only three squid studied, no firm conclusions could be made from this first experiment, but the team are now confident that the squid and their bacteria can survive the long trip, paving the way for plenty more space squid experiments in the future.
3 Growing tomatoes in space Young people across the US and Canada are working with NASA to find ways of growing food in space. Throughout the school year, 1.2 million tomato seeds will be sent out to 18,000 schools. Half of these seeds have already made the journey to space and back, spending five months on board the International Space Station under the watchful eye of NASA astronaut Scott Kelly. The students do not know which are the space seeds and which have stayed on Earth, so they will treat both the same, planting them, then watching and recording as they germinate and grow. This will teach
the students about plant life cycles and how to go about conducting rigorous scientific studies. Each school will then submit their data, informing NASA how many seeds they planted, and how many actually grew. The results will help scientists to understand what happens to seeds when they are taken into space, and will be used to help plan missions to Mars. During the two-year journey to the Red Planet, the crew would need to grow tomatoes that are not only nutritious, but also have leaves that can produce clean drinking water, that can be captured as it evaporates.
3 Time in space The seeds spend five weeks in microgravity, orbiting the Earth at 7.7km (4.8mi) per second.
4 Back to Earth The seeds return to Earth, where they are delivered to thousands of schools across North America.
2 To the space station The seeds travel to the ISS on board the SpaceX Dragon, a privately owned cargo spacecraft.
5 The experiment The students do not know which seeds have been to space so that both types are grown in the same conditions.
1 Preparing the seeds
6 Citizen scientists
600,000 seeds are prepared and packed ready for the journey into space. Another 600,000 remain on the ground.
Since the experiment started in 2001, more than three million students have become space tomato experts for NASA.
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Controlling rovers from the ISS
The ISS crew keep fit using specially designed equipment
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How space travel affects the human body
The crew on the ISS spend over an hour every day exercising. This is not only vital for their wellbeing; it also helps scientists to gather information about the effects of space on the human body. There are three main pieces of gym equipment on board the space station – an exercise bike, a treadmill, and a weights machine – each of which has been modified for the conditions onboard the ISS. A standard weight machine would not work without gravity, so the ISS Advanced Resistive Exercise Device uses pistons and vacuum cylinders instead. The astronaut has to pull against the vacuum to move the machine, and specially designed
flywheels help to make it feel more like lifting weights on Earth. When using the treadmill, the crew members are strapped down at the waist with bungee cords and on the bike, their shoes are attached to the pedals with special clips. There is no point in having a seat on a space bike because in microgravity, the cyclist does not need to sit down. Before, during or after exercise, the crew can take part in experiments for researchers back on the ground. They gather saliva samples, record heart rate and breathing, use accelerometers and force plates, and even capture video footage, allowing scientists to learn more about what happens to the human body in space.
In June 2013, flight engineer Chris Cassidy took control of a K10 robot at NASA’s Ames Research Center in California, not from the ground, but from his station on the ISS. He drove around a simulated moonscape for three hours, demonstrating the future technology that could allow astronauts in space to send robotic scouts to the surface of other worlds. K10 is a four-wheel drive robot, weighing about 100 kilograms (220 pounds). It borrows technology from undersea exploration and is not just remote controlled, but can also intelligently plan its route across the terrain. K10 moves at a slow walking pace and builds a 3D picture of its environment using a combination of cameras and a scanning laser. K10 is also able to deploy radio antenna, becoming a mobile communications platform. The technology is being tested for a possible NASA Orion spacecraft
mission, which aims to take a crew into orbit around Earth behind the far side of the Moon. With technology like this, astronauts could use a remotecontrolled robot to deploy a radio telescope onto the unexplored surface. The Moon would shield the telescope from Earth’s radio chatter, allowing us to peer even farther out into the universe.
5 3D printing without gravity
3D printing would be an important step towards living in space
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Imagine what space travel would be like if new tools could be delivered to astronauts at the touch of a button. That is the aim of Made In Space, Inc. and its 3D printer on the ISS. In November 2014, NASA astronaut Barry “Butch” Wilmore became the first person to use a 3D printer in space. After a few test runs, a Made In Space engineer sent the plans for a wrench to the ISS for the first test of on-demand printing. Four hours and 104 layers of plastic later, the wrench was finished.
Operating a 3D printer in space, without gravity, is a huge technical challenge. On Earth, gravity helps the plastic to sit in neat layers as it is extruded, but on the ISS the components would float around. Made In Space has tackled this problem with some innovative, but top-secret technology. In February 2015, the printed objects were sent back to Earth to be examined and compared with versions of the same objects that were printed on the ground.
10 amazing space station experiments K10 borrows and advances technology from undersea exploration
Flight engineer Chris Cassidy controlled a robot in California from the ISS
7 Stem cells with flatworms Flatworms are some of the simplest life forms on the planet but they have an incredible ability: if you cut them in half, each piece will grow into a fully formed flatworm. This is down to a network of stem cells positioned throughout their bodies, ready to spring into action if damage occurs by dividing and changing to form the cells needed to build brand new tissues and organs. Scientists are starting to understand how this process happens on Earth, but wondered if the stem cells would still function without gravity. This could be important in understanding
how growth and repair in our own bodies might change in space. The flatworms have travelled to the ISS and back again in sealed tubes, where they were monitored to see how well they repaired themselves. The activation of various genes was also tracked, and will be compared to the patterns that we see back on Earth. NASA isn’t just interested in the health information that can be gathered from this research. They are also investigating how biological processes could inspire technology that repairs itself whilst still in use, like a living thing.
Single head
Bipolar head
Triple head
Quadruple head
Under certain conditions, flatworms can generate multiple heads
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There's no need to miss a caffeine fix, even in space
8 Making coffee in Earth-orbit Making hot drinks in space is a complex business, but not content with the idea of a life without coffee, the Italian Space Agency teamed up with space food engineering company Argotec and coffee giant Lavazza to design a machine that could be used in microgravity. Water at high temperature and pressure is difficult to manage in space, so the project was a serious engineering challenge. Plastics had to be replaced with steel tubing capable of withstanding pressures of up to 400 bar (400 times the air pressure at sea level), and the finished product weighs
a hefty 25 kilograms (55 pounds). The ISSpresso machine works in a similar way to the coffee machines back on Earth, and even uses the same Lavazza coffee capsules. It can also make tea and broth. An astronaut in need of a hot beverage just has to follow these simple instructions. Plug the machine into a utility outlet panel and install a water pouch. Install a NASA standard drink bag, and a capsule containing the desired drink. Three minutes later, the drink is ready. Astronaut Samantha Cristoforetti. was the first to enjoy a coffee in space.
3 Heating Once the water has been pressurised, it is heated to the right temperature.
4 Coffee capsule Hot water passes through a coffee capsule, and the fresh coffee is pushed into the pouch.
5 Pressure difference
2 Water in
A pressure differential is created inside the pouch so that when the straw goes in, the fresh coffee smell rushes out.
The water is taken into the machine and pressurised, passing through a series of steel tubes and into the heater.
1 Water pouch The astronaut first fills a pouch with water, and then fastens it to the coffee machine.
6 Coffee time The whole process takes just three minutes, barely longer than you have to wait for a coffee back on Earth.
9 Testing inflatable homes
The BEAM is due to be carried to the space station in 2015 on board a SpaceX Dragon capsule
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Humans are going to need places to live when we travel to the Moon, Mars and beyond, and where better to test them than the ISS? The Bigelow Expandable Activity Module, or BEAM for short, is due to be carried to the space station in 2015 on board SpaceX Dragon. Packed up, the BEAM only measures 1.7 x 2.4 metres (5.7 x 7.8 feet), but when filled with pressurised air, it inflates to form a space that is 3.7 x 3.3 metres (12 x 10.5 feet), about the size of a small bedroom. It is made up of many layers, including an air cushion and a shield that will protect the structure from damage by dust and debris.
In the case of a collision with a larger object, the inflatable room is designed to leak air slowly, allowing the astronauts on the space station plenty of time to react. When it arrives, the module will be docked with a module of the ISS called the Tranquility node, but it will not be ready for use straight away. It first needs to be tested, so temperature, pressure and radiation readings will be recorded around the clock, and astronauts will enter every three months to take measurements and to perform an inspection of its condition. If all goes well, inflatable rooms might become an integral part of our space habitats.
10 amazing space station experiments
10Hunting for dark matter (AMS-02) weighs 8,500 kilograms (18,740 pounds) and was delivered to the ISS on the penultimate voyage of the Space Shuttle Endeavour. Since 2011, AMS-02 has been monitoring for signs of antimatter, dark matter and dark energy – the missing pieces of the universe. Assembled at CERN, the home of particle physics, AMS-02 is a particle detector. At its core is a huge magnet, which measures the charge of any
particle coming in, and an arsenal of instruments identify other properties, including a ‘stopwatch’ that times the particles as they pass through. AMS-02 is searching for cosmic rays, which are extremely high-energy radiation, some of which may be charged particles released when dark matter collides. So far, it has recorded 54 billion events, and will continue into the hundreds of billions, looking for signs of the missing universe.
Transition radiation detector
Time-of-flight scintillator
This detector can tell the difference between particles by the X-rays that they release – important for spotting antimatter.
The AMS-02 team describe this component as the 'stopwatch'. It measures how long each particle takes to pass through the detector.
Silicone tracker The tracker measures the path of the particles as they are bent by the superconducting magnet, detecting the difference between matter and antimatter.
Permanent magnet The superconducting magnet bends the path of charged particles as they pass, and can separate particles from antiparticles.
Ring imaging Cherenkov counter This detector is able to identify the type of charged particle by measuring the radiation that it emits as it passes through.
Electromagnetic calorimeter
@ Ed Crooks; NASA
Something about the universe doesn’t quite add up. Everything that we can see – from stars and planets to galaxies and black holes – only represents around five per cent of what is known to be the total mass and energy in the system. Where, and what, is the other 95 per cent? A total of 56 institutes from 16 countries around the world have come together to find the answer. The Alpha Magnetic Spectrometer
As high-energy cosmic particles hit the lead surface of this instrument, they produce a shower of low-energy particles, and the patterns can reveal their identity.
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Have you ever wondered how different your life would be if you had made different decisions to the ones that you had? If you had turned right instead of left? You may never know what may have been, but incredibly, all those ‘what if’ scenarios may have played out somewhere. That’s because over the past few years support for the idea that we live in a ‘multiverse’, in which our universe is just one tiny bubble among countless others, has been gaining strength. How would a multiverse arise – and just how similar, or different, would the many universes within it be? For a lot of people, the term ‘multiverse’ conjures up pictures of parallel realities, some perhaps with just a slight difference from our own. And in fact, that sort of multiverse is indeed predicted by the ‘many worlds’ interpretation of quantum mechanics – the strange but highly successful model of how the universe works on the smallest scales – wherein every possible quantum state branches off into a
Inflation: proof for a multiverse?
new universe. In other words, every action that is physically possible – every choice that can take place – can happen and will happen, somewhere. Such parallel universes might exist, and evidence for this ‘many worlds’ interpretation of quantum mechanics that invokes them might one day be found, but they would be forever unobservable, and separated from our universe in ways we can hardly comprehend. Cosmologists like Matthew Kleban are instead interested in a more concrete form of multiverse – something beyond the realm of our current universe, but which we might nevertheless learn about. “We have a horizon in cosmology that’s a lot like the horizon on Earth,” explains Matthew Kleban, associate professor of physics at New York University and a leading multiverse theorist. “If you’re on an island in the ocean and climb to the highest point, there’s a finite distance you can see, and you don’t know what’s beyond that horizon by directly seeing
Cosmic Microwave Background After about 380,000 years, subatomic particles known as electrons cool enough to combine with protons. The universe becomes transparent to light and the microwave background starts to shine.
Big Bang In an infinitely dense moment some 13.8 billion years ago, our universe is born from a singularity.
Rapid inflation According to the theory of inflation, the universe expanded rapidly for a fraction of a second after the Big Bang. The easiest way to visualise the inflation of the cosmos is by blowing up a balloon and drawing galaxies on it – you will see the galaxies move away from each other as you blow air into the balloon.
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“Do we live in a ‘multiverse’ in which our universe is just one tiny bubble among countless others?”
Dark ages
First stars
Clouds of dark hydrogen gas cool before joining together.
Gas clouds collapse and fusion of the stars begins.
Why we live in a multiverse
it. But you still might be able to get information about it, like say a log comes floating up to your island, with some plants growing on it. You can learn things from over the horizon because signals of various sorts can reach you from beyond it.” In the case of our universe, the horizon is a lot further away than a horizon on Earth – in fact it’s about 46.5 billion light years away from us, in every direction. This apparent ‘edge’ to the universe is caused by the limited speed of light, and the fact that the universe is expanding rapidly from the Big Bang – the hot, dense state in which it originated. According to the best current measurements, the Big Bang happened 13.8 billion years ago, and so we can only ever see objects whose light, travelling at 299,792 kilometres (186,282 miles) per second, has had time to reach us. In fact, because the very early universe was so dense, it formed a brilliant opaque fireball that only became transparent after about 400,000 years.
Light from that fireball – transformed into invisible microwave radiation in its long journey across expanding space – is the most distant thing we can directly observe, and as we’ll see, this ‘Cosmic Microwave Background Radiation’ (CMBR) has a key role to play in the search for evidence of a multiverse. Its true distance is estimated at 46.5 billion light years because, although the most distant light has been travelling for 13.8 billion years, the space it has been moving through has been expanding during that time. “We don’t know what’s beyond the horizon,” continues Kleban, “but what we can do is extrapolate from what we can see. On those large scales, the universe is pretty much homogeneous and isotropic, meaning it’s pretty much the same in all directions and as far as we can tell the same in every place. So there’s definitely a wider universe that’s much bigger than what we can see, but it may not be very interesting. That’s a basic assumption of modern
Associate professor of physics at New York University, Matthew Kleban believes that it is highly likely that we live within a multiverse
Galaxy formation Gravity causes galaxies to form, merge and drift. Dark energy accelerates the expansion of the universe, but at a much slower rate.
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The Planck telescope being prepared for tests at ESA's European Space Research and Technology Centre (ESTEC) in the Netherlands
cosmology, that we now call the cosmological principle.” Quite how far these distant reaches of spacetime stretch is an intriguing question – and one that depends on the shape of space itself. Estimates range from about 250 times the size of the observable universe (for a ‘closed’ and finite universe in which space curves inwards like a sphere), to infinite (if space is flat or ‘open’, curving outwards like a saddle). However far space stretches, though, we’d expect parts of this wider
universe to be essentially similar to our own. In fact, if the universe really is infinite, or close to it, we’d expect there to be parts of the universe, far, far away from us, that are exactly like our own observable universe. How far away would these replica ‘universes’ – and the replicas of ourselves that would live in them – be? Our observable universe, with its radius of 46.5 billion light years, has enough room for 10118 Matthew Kleban particles. Try to imagine all the different ways these particles can be arranged –
“ Eternal inflation would explain one of the biggest mysteries about our cosmos”
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mathematics tells us that there are 2 to the 10118 different arrangements of all these particles and that we would have to cross 10 to the 10118 metres – that’s 10 to the power of 10 with 118 zeroes after it – before we encountered another duplicate universe with duplicate versions of us and our friends, living out parallel existences. That is a long, long way – in comparison, our observable universe is just 8.8 x 1026 metres across – but if the universe is infinitely big, then there is enough room for the particular arrangement of particles making up our universe to be repeated again and again. What if there’s another type of multiverse out there – one in which universes pop into existence like bubbles and have the potential to be radically different from our own? That’s the intriguing possibility that fascinates Matt Kleban and many of his colleagues and at its heart lies a concept called ‘eternal inflation’.
Why we live in a multiverse
Data from ESA's defunct Planck satellite is being used in an attempt to prove the multiverse theory
Planck scanned the sky to make the most accurate map ever of the CMBR
Working out what we would see if a multiverse exists will help us to know what to look for
“In everyday life we’re familiar with the phases of matter – if you think about a water molecule, for example, that can be liquid water, ice or steam. But in fundamental physics it’s not just substances that have phases, but everything around us – space and time themselves. Theories like String Theory [the leading theory of high-energy theoretical physics] predict a large number of phases, differing a lot more than ice differs from water. They would have different laws of physics: for instance the fundamental particles of the cosmos, such as electrons and quarks, might not exist in some other phase, or they might have some different form, or different properties like electrical charge and mass. These phases are kind of a generic feature of most modern cosmological theories.” Among the various properties that could change from one phase to another is the strength of the ‘vacuum energy’ that permeates empty space. In the past couple of decades, astronomers have
“ Outside of our bubble could be something exotic, rapidly inflating, and with different laws of physics”
discovered strong evidence that a small amount of this energy in our universe – better known as ‘dark energy’ – drives the expansion of the cosmos to accelerate when it should be slowing down, but in other phases it might be nonexistent, much stronger, or even have a negative value. This, it turns out, is key to creating new universes in this kind of multiverse. If all these different phases can exist, of course, then there should be transitions between them, just as there are between ice, water and steam.
“You could have a universe that at some initial time has a single phase everywhere,” Kleban explains, “but bubbles of different phases will inevitably appear more or less at random, like bubbles appearing in champagne. It’s sort of a coin flip whether a given phase would have positive or negative vacuum energy, but at least some of them will be positive, and if the vacuum energy is large, then the bubble expands exponentially, doubling in a fraction of a second, doubling again after that, and so on. So the volume will just explode in those regions. And if those phases are themselves unstable, then bubbles will appear inside them – that’s what we call eternal inflation.” It’s a fairly mind-blowing concept, as Kleban admits: “If all this is correct, then we may be inside one of these bubbles, and outside
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of it is something that’s probably extremely exotic, most likely very rapidly inflating, and has different laws of physics – perhaps even different numbers of dimensions. Once you go beyond the wall of our bubble, the multiverse isn’t at all boring and isotropic after all.” Eternal inflation would explain one of the biggest mysteries about our cosmos. The properties of the universe seem suspiciously fine-tuned for life. For example, if the gravitational constant were a little stronger, or the charge of an electron a little smaller, or the force that binds particles together weaker, then stars and planets would not be able to form and we would not be here. Everything is ‘just right’, like Goldilocks’ porridge, and so far no one has been able to explain why. However, if there are an infinite number of bubble universes, all with slightly different properties, then there is bound to be a universe – our own – where the properties are just right, which would explain why we can exist. One of the big questions, of course, is whether we could ever hope to find evidence that would prove the theory – or at worst, prove that this cannot be the case (a key test of whether a theory is truly scientific – technically referred to as ‘falsifiability’). The idea that the multiverse theory cannot be proved or disproved has been a common criticism from sceptics, and it’s an area where Matt Kleban has been concentrating much of his work and research. “What’s nice about the theory is there are observational consequences – if other bubbles form close enough to us, then they’ll collide with our own bubble. Detecting the consequences with our current technology is a long shot, but it’s not impossible, and you can actually work out what you would see, and therefore know what to look for. So the theory makes testable predictions, and it also makes falsifiable predictions – it predicts that our bubble would need to have an open spatial geometry – if we measure the geometry of our universe and it turns out to be closed, then that would falsify the whole thing.” So what traces would a collision with another bubble make on our universe? As you might expect, a collision between two universes is a highly energetic event. “The walls of these bubbles are extremely rigid, and moving at speeds very close to the speed of light, because there’s a force that drives their expansion,“ enthuses Kleban. “The bubble naturally wants to expand and ‘eat up’ the vacuum energy around it. That gets converted into the kinetic energy of the wall, so these things accelerate, going faster and faster, until they collide. The result is a wave of energy injected into our own bubble, and this propagates across our universe in what we call a ‘cosmic wake’. All sorts of things are affected, but the most important is the Cosmic Microwave Background Radiation. That’s what we want to look at, because it’s the oldest and most distant radiation, so it’s had the most time to be affected by this sort of event.” According to most simulations of the event in question, a collision between universes would show up as a ring of slightly higher temperature amid the otherwise more or less random variation of the CMBR, and also as a polarisation pattern within the radiation – instead of the microwaves vibrating in random planes, their oscillations would be aligned in specific directions.
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The different types of multiverse From unseen regions of spacetime to complex structures, there are four distinct levels
Level 1
Where an identical Earth exists The simplest multiverse is one that most certainly exists – the Big Bang model of cosmic origins predicts that every point in the universe has a ‘Hubble volume’ around it, limited by the expansion of the universe and the distance light has been able to travel in the 13.8 billion years since the infant universe became transparent. In practice, this means our Hubble volume is a sphere 93 billion
light years across, but there are many more Hubble volumes extending far beyond what we can see. If the universe has a closed geometry, the number is limited as space curves back around on itself, but if the universe is open (as seems most likely), there may be an infinite number of Hubble volumes, each containing a universe, meaning that somewhere out there, other planets virtually identical to Earth exist.
Level 3
Where your future self exists According to the so-called “many worlds interpretation” of quantum mechanics, every decision point between alternative outcomes – even on the tiniest microscopic scale – sees the universe branch into two mutually unobservable realities. This astonishing idea would involve the creation of multiple universes not in the few-dimensional space described by string theory, but in an infinitedimensional geometric structure called a Hilbert
space. Although you might imagine the many worlds interpretation giving rise to a more varied multiverse than an extended or bubble model, the reality is that since all three are infinite, the same variety will play out across all types. What’s more, some physicists have even argued that if quantum mechanics works in a certain way, then the many worlds version of the multiverse could be formally equivalent to the more mundane ‘single-geometry’ versions.
Why we live in a multiverse Level 2
The expanding universe we can’t reach String theory, a potential grand unified theory that aims to explain the fundamental laws of particle physics, suggests that spacetime has at least ten dimensions, of which we experience just four (three dimensions of space, plus time) in our own universe – the others are tightly curled around each other so we don’t perceive them. But our arrangement of dimensions, or phase, is just one among many possible phases – given the right conditions, new ones can pop into existence within a pre-existing phase and then expand rapidly at the speed of light, meaning that they are completely unreachable. This theory of eternal inflation gives rise to a potentially infinite number of bubble universes with different dimensions and laws of physics.
“If the universe is infinite, we’d expect there to be parts of it that are exactly like our own observable universe” Level 4
The strangest universe of all As if the ideas of a multiverse as an extension to our own universe, a series of interconnected bubbles, or a branching structure of infinite dimensions weren’t strange enough, cosmologist Max Tegmark of the Massachusetts Institute of Technology, argues that all of these “lower-level” multiverses are simply limited examples of an overarching mathematical multiverse called the “Ultimate ensemble.” This encompasses all possible multiverses that can be abstracted from the messy details of terminology into a purely mathematical description, and therefore includes all the lower-level multiverses, plus any other types that still remain to be discovered. This, however, is merely part of Tegmark’s semi-philosophical argument that the entire multiverse is a mathematical structure within which conscious entities perceive a physically “real” world.
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“So far astronomers haven’t found any strong evidence for such collisions, but there are some anomalies in the CMBR that look a little bit like bubble collisions. I don’t take them very seriously, but imagine there really was something there on the verge of detectability – it would produce an anomaly of marginal significance and at first no one would take it seriously, so I guess that you can’t rule it out. Currently we’re waiting on a major new piece of data in the form of an all-sky polarisation map from the Planck satellite. That’s a partially independent piece of data from the temperature maps, and certain types of bubble collisions would have a very distinct signature in the polarisation.” If our universe does turn out to be just one among, perhaps, infinitely many in a multiverse, the implications for cosmology would be huge. No longer would we imagine space and time as being created in a single event 13.8 billion years ago – that
would simply mark the point when our particular phase popped into existence and began to expand. It would at last be meaningful to ask what came before the Big Bang, but in the process we would be forced to exchange our current view of a relatively young universe with a specific beginning for a multiverse, whose origins, if indeed their were any, lay in the unknowable distant past. But as Matt Kleban is keen to point out, the study of our potential multiverse is still in its infancy. “We focus on certain types of collision because it seems like those would be the ones we’d have the best chance of observing, but there could be something that we have missed. And the other possibility is an entirely different type of observation that we can’t yet do, or haven’t thought of. The important thing is that it is possible to detect the multiverse, and once something’s possible, we may discover a clever way to do it. We’re really still at the beginning.”
“There are some anomalies in the CMBR that look a little bit like bubble collisions” Matthew Kleban
There is growing evidence that we live in a multiverse, with multiple Big Bangs bringing other universes into existence
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Why we live in a multiverse
Life in the multiverse Confirmation of a multiverse could raise some intriguing questions about the origins of life and our own place in the cosmos. According to our current understanding, the physical laws of our universe are suspiciously fine-tuned for life to arise – a tiny difference in any one of several physical constants might make liquid water much rarer, render complex organic chemistry unworkable, or leave matter itself unable to hold together. The usual scientific solution to this problem, called the ‘weak anthropic principle’, simply states that if the laws of the universe did not have the particular behaviours we
observe, then we would not be around to see them – so we shouldn’t be so surprised. Various ‘strong anthropic principles’, meanwhile, take things a step further with the assumption that for some reason or other, the universe has to give rise to something like its present set of life-friendly parameters (perhaps even because, borrowing an idea from quantum theory, the existence of conscious observers is a requirement for the universe to exist). If this universe is just one within an infinite multiverse (particularly an ‘eternal inflation’ or ‘many worlds’ multiverse), this could significantly
change the terms of the debate. The odds of a universe arising with our own parameters would rise from highly improbable to a locked-in certainty, but at the same time so would the odds of any other combination of parameters. So could life exist in these other universes? According to some researchers, it may be far more robust than previously realised – using computer simulations to study the evolution of universes with various fundamental constants, they have found that stable forms of matter and carbon chemistry can arise in a surprising variety of situations.
@ Tobias Roetsch; NASA; WMAP Science Team; ESA; SPL
The physical laws of our current universe are suspiciously finetuned for life to exist
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WHAT HAPPENED BEFORE THE
Could there have been a time before the birth of the universe?
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What happened before the Big Bang?
Here’s an astounding thought – one that questions the beginning of existence itself: could there have been a time before the Big Bang? In other words, could the universe have existed before we thought it had even started? May there have even been previous universes? Such ideas, once the preserve of high-concept science fiction and philosophical debates, are gaining a new scientific credibility in the 21st century. Some cosmologists are wondering if the Big Bang was merely an intermediate phase and not the true start of the universe at all. Theories such as the ekpyrotic universe, ‘big bounce’ models and cyclic cosmology have all been around for a while, but new data from sensitive space probes could put some of these on a firmer footing. But what exactly was the Big Bang anyway and why are some scientists now changing their minds about it? The widely accepted standard cosmological model states that the universe came into being from a super-hot, super-dense state that was no bigger than an atom and made of pure energy. Not much about that is contentious but things get precarious with what happens next. This object, known as the ‘initial singularity’, is thought to have been timeless and dimensionless; there was nothing ‘outside’ of the singularity to speak of. Then 13.82 billion years ago (a figure obtained from NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) and ESA’s Planck satellite), this microscopic singularity expanded rapidly to the size of a football. This was the ‘Big Bang’. And despite lazy descriptions, it wasn’t an explosion. The universe never exploded into being. Rather, this initial expansion from microscopic quantum fluctuations birthed space and time and seeded the large-scale structure of the universe. This ‘Big Bang’ model has served cosmology well for over 80 years, but there have always been unanswered questions. Despite the Big Bang being the cornerstone of cosmology, a theory called cosmic inflation was proposed in the 1980s to address some of the problems with the original model, such as the horizon problem (i.e. how has the universe ‘homogenised’ on the largest scales when it hasn’t existed for long enough to do so, given its enormous size?). Cosmic inflation theory proposes an extremely rapid initial expansion rate of 10-32 seconds. The universe would then have continued expanding in line with the Big Bang theory. As the universe expanded it also cooled, which resulted in energy condensing into matter known as subatomic particles. This transformation of energy into matter, predicted by Einstein’s theory of special relativity, is described by the most famous equation in science: E=mc2. The universe (still seething and hot) was then a dense morass of quarks and electrons, with photons of electromagnetism, including those of visible light, trapped within it. After 380,000 years this still-expanding universe cooled enough for the first chemical elements (hydrogen, helium and lithium) to form. The morass of quarks turned into the protons and neutrons of atomic nuclei and captured free-travelling electrons in the process to make fully-fledged atoms. This was the point at which all of the trapped photons of the electromagnetic spectrum could now travel
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unhindered. In other words, the universe became transparent. But it was still dark; it took another 400 million years for the first stars and galaxies to form. Dense hydrogen and helium gas clumps collapsed under gravity (possibly collecting within a large ‘dark matter halo’), until atomic nuclei in their cores began fusing together, known as thermonuclear fusion, which released large amounts of energy as the first stars came alight. Galaxies of such stars formed within these haloes. It’s strange to think that our universe could have existed before any of these events, but the Big Bang wasn’t always accepted. The eminent British astronomer Sir Fred Hoyle, who coined the term ‘Big Bang’ in a BBC radio interview in 1949, actually hated the idea himself. So why did it take such a hold in cosmology? In 1912 the American astronomer Vesto Slipher saw that the spectra of galaxies were Dopplershifted towards the red end of the electromagnetic
spectrum. This showed they were moving away from us at speed. Then in the 1920s, Alexander Friedmann, a mathematician in the Soviet Union, and Belgian astronomer Georges Lemaître both independently proposed the idea of an expanding universe, which could explain Slipher’s observations. But reception to Friedmann and Lemaître’s idea was lukewarm. Even Albert Einstein – upon whose general theory of relativity their hypothesis was based – didn’t accept the idea at first. But in 1929, Edwin Hubble showed that the recession speeds of the galaxies actually increased with their distance from Earth. This meant that if the universe was a movie played backwards, then all galaxies would have once ‘existed’ at the same point in space and time. Friedmann and Lemaître were vindicated and the speed-distance relationship became known as ‘Hubble’s law’. In light of all this, English astronomer Arthur Eddington invited Lemaître to speak in London
“If the universe was a movie played backwards, all galaxies would have existed at the same point in space-time”
(Friedmann having died four years earlier), calling his solution “brilliant”. Lemaître posited the idea of a universe expanding from a single point, which he described as a ‘primeval atom’ or an ‘exploding cosmic egg’. This is what cosmologists now call the initial singularity, the point of the Big Bang – although it wasn’t actually an atom (or an egg). Einstein conceded his mistake (even when his own calculations had shown an expanding universe) and accepted Friedmann and Lemaître’s ideas. Unlike Einstein and others, Hoyle actually had no problem with an expanding universe. What he hated was the idea of a ‘beginning’. As an avowed atheist, Hoyle couldn’t accept a point of creation and thus a potential ‘creator’. He clung doggedly to the steady state theory: the idea that the universe had always existed and was perpetually creating and destroying. But Hoyle was on the losing team. In 1948, American cosmologists Ralph Alpher and Robert Hermann predicted a background radiation to space – the residual heat ‘echo’ just before the universe became transparent 380,000 years after the Big Bang. As space had expanded for billions of years since, this radiation’s wavelength should have been stretched into the microwave region. Just 14 years later it was finally discovered by physicists Arno Penzias and Robert Wilson, using the Holmdel
Once atoms formed in the early universe, the resulting gas clouds collapsed to form stars
What is a singularity? Singularities are regions of space and time with extreme gravity (not even light can escape) and infinite density. They are thought to exist inside black holes, and our universe is thought to have started from one, too. Although predicted by the general theory of relativity, neither that or quantum mechanics can explain singularities. They remain truly mysterious to science.
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www.spaceanswers.com
What happened before the Big Bang?
What is the Big Bang? Time after the Big Bang: 0 seconds
The beginning The absolute beginning of our universe (according to the Big Bang theory), which starts out as a dense, hot, timeless, dimensionless singularity.
Cosmic inflation 10 -36 seconds
A rapid expansion phase after the Big Bang increases the size of the universe from that of an atom to a football. The universe is made of pure energy.
Cooling and quarks 10 -32 seconds
After inflation ends, the universe cools enough for subatomic quarks, electrons and other particles to form from the available energy.
Atoms form 380,000 years
Further expansion and cooling means subatomic particles form into atoms. Hydrogen, helium and lithium fill the universe, which now becomes transparent as a result.
First stars and galaxies are born 400 million years
Hydrogen and helium gas clumps collapse under gravity to form the first stars. They form inside galaxies, which lie in dark matter haloes.
Present day 13.82 billion years
www.spaceanswers.com
Several generations of star formation and destruction creates and spreads chemical elements throughout space. That in turn creates planets with complex chemistry and even life.
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Planck satellite data could show if there was a time before the Big Bang
Temperature fluctuations in the CMB radiation, measured by ESA’s Planck Satellite
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Horn Antenna. Initially believing it to be caused by bird droppings, they soon saw that the spectrum of this Cosmic Microwave Background (CMB) matched the predictions of the Big Bang model. The steady state theory had no explanation for the CMB and was therefore royally defeated. Alongside the work of Slipher, Friedmann, Lemaître and Hubble, Penzias and Wilson’s evidence showed that the universe did have an origin after all and had been expanding. The Big Bang theory was king. And yet, despite its enormous success, there has always been something that scientists have never liked about the Big Bang: it doesn’t explain the initial singularity itself. Where did it come from? Why is it simply assumed to have been timeless, dimensionless and infinitely dense? Scientists hate assumptions, especially regarding the big questions. Even cosmic inflation theory (developed by physicists Alan Guth, Andrei Linde and Paul Steinhardt), which successfully ironed out some of the problems of the Big Bang, couldn’t explain the singularity. As a result, alternatives to these cosmological cornerstones have been proposed and it’s from this that the idea of a pre-Big Bang existence has arisen. Strangely, these ideas may even be supported by the very same CMB data that supports the Big Bang theory. In 2001 Steinhardt worked with Neil Turok, Justin Khoury and Burt Ovrut on the ‘ekpyrotic’ model of the universe; an alternative to inflation. In their original hypothesis the universe was birthed from a collision between two multidimensional membranes (or ‘branes’) floating through a higher dimension of space, as opposed to our three dimensions (imagine a pair of flat, rippling ocean surfaces meeting along a third dimension). After the universe was created from the collision of the branes, the ekpyrotic phase would occur. This would also apply to a contracting brane. Imagine a prolonged contraction of a previous universe eventually collapsing back into a singularity, before restarting again as our present universe in a typical ‘Big Bang’ scenario. The conditions for our universe (its fundamental laws and seeds for a future large-scale structure) would have been set in the previous universe, and not by inflation. This scenario involving branes and multidimensions seems quite exotic, but more up-to-date forms of the ekpyrotic model mostly do away with these multidimensional branes and other exotica. The newer models simply apply the physical constraints of the Big Bang theory. A researcher working with one such form of the ekpyrotic scenario is Dr Yifu Cai of McGill University in Canada. He says, “Since Neil, Paul, et al proposed their original scenario, the physical picture is very clear. Their cosmological model is able to dilute unwanted relics [of the Big Bang] via the ‘ekpyrotic phase’. But the universe is still expected to pass directly through the singularity from the contracting to expanding phases without that being removed.” He means that in the multidimensional scenario, although ekpyrosis can ‘smooth out’ some problems like cosmic inflation can, the singularity is still present and the physics surrounding that are as vague and problematic as ever. But Dr Cai’s work, performed with Professor Robert Brandenberger does away with singularities entirely.
What happened before the Big Bang?
In their model a previous universe collapsed until it could go no further and then ‘bounced’ out as a completely new universe. “In our scenario, the whole of cosmic evolution then becomes smooth. The physics around the bounce, including the background [CMB] and perturbation, are well controlled and calculable,” he says. By removing the singularity, a lot of associated problems (such as infinite densities and zero dimensions – which have little support in physics) are also removed. Cai and Brandenberger’s work also predicts the existence of the CMB and the microscopic perturbations that grow to become the universe’s large-scale structure. This is even consistent with the latest data from the WMAP and Planck probes. So could the CMB contain hints of a previous universe that we could detect in some way?
Many cosmologists have asked themselves that very question. One scenario that has an answer is a cyclic model of cosmology. With their concept of universes perpetually oscillating between expanding and contracting phases, cyclic cosmological theories have a lot in common with the ‘big bounce’ models (and in fact, there is a lot of overlap). The idea has been around since at least the 1920s and one variant was even proposed by Einstein in 1930 after accepting Hubble’s observations supporting an expanding universe. Generally speaking in the cyclic scenario, after an expansion phase the universe would slow, then stall, and would then contract back due to the gravitation of all the matter within it. This would culminate in a ‘big crunch’ or a 'big bounce', which would then be followed by a new expansion phase, and so on. Einstein thought that
“Our universe could be the interior of a black hole that exists in another universe” Nikodem Popławski, University of New Haven
this cyclical scenario could be a better, more longterm alternative model to the simpler idea of an expanding universe with a single origin point. But in 1934 American physicist Richard Tolman showed that such cyclic models (Einstein’s included) couldn’t work the way people wanted them to because of the second law of thermodynamics. Over time, the amount of disorder (entropy) in an oscillating universe would only ever increase and the amount of usable energy within it would only ever decrease. Every expansion would be slower and larger than the previous one, as each contraction phase would only go back so far and less energy would be available for each new expansion phase. Conversely then, previous phases would have started out smaller and smaller until you eventually returned to a ‘big bang’ scenario again anyway. But in the age of WMAP and Planck, the idea of cyclic, oscillating universes has re-emerged. One such example, Conformal Cyclic Cosmology (CCC), was developed by English physicist Sir Roger Penrose and Armenian mathematician Vahe Gurzadyan in 2010, and is based on the theory of general relativity. Using data from both
Supermassive black holes may be gateways to other universes
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Space Science
What caused the birth of the universe? Many scenarios illustrate how our universe may have come into being
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There was nothing
Strictly speaking, no scientist believes that our universe started from literally nothing. There always has to be something to cause another action to occur. However, many cosmologists are not yet convinced that there was anything before the Big Bang. Lawrence Krauss is one such scientist and he’s developed a theory of ‘quantum nothingness’ from which the universe could have originated. The theory involves so-called 'virtual particles', which flit in and out of existence for fractions of a second in empty space. They are predicted by quantum theory and their effects can be observed. Krauss says that if you remove virtual particles from a region of space it still has an energy density – but it shouldn’t. It’s from this form of ‘nothing’ that our universe could have started.
Virtual particles, predicted by quantum theory, flit in and out of existence for fractions of a second in empty space
BACKED BY
Professor Lawrence Krauss Arizona State University
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There was another universe before ours BACKED BY
VOLUME (of the universe)
Sir Roger Penrose Bedford College London, Princeton University, Wadham College Oxford
TIME Big Bang and expansion
Everything now stalls
Universe in reverse
Big bounce and next phase
In the cyclic model, a universe may have a true origin as normal and go through an inflation and expansion phase.
In a cyclic universe the cosmos may expand to a point and then stall. This may happen from the gravitational effect of the matter within it.
Gravity takes over and the universe now contracts, with galaxies moving towards one another instead of further away.
Inevitably, the universe can only contract so far. A ‘big bounce’ initiates the next expansion phase. The process continues, with each phase getting larger and slower.
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What happened before the Big Bang?
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It’s always been there BACKED BY
Professor Gabriele Veneziano CERN and Collège de France
TIME An empty infinite universe
Expanding internal region
A big crunch
The Big Bang
In this scenario, the universe has existed forever and was nearly empty for that time. Then gravity took over and matter started to clump together.
The density of matter is such in some regions that it forms an incredibly massive black hole, the internal region of which experiences an expansion.
Inside the huge black hole, matter again collapses under the intense gravity and increases in density up to a limit imposed by physics.
When it can’t stand any more, quantum fluctuations cause the matter to expand outwards in a typical Big Bang scenario within its black hole universe.
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It is one universe of many
Eternal inflation theory was proposed in 1983 by physicist Paul Steinhardt as an extension of the cosmic inflation and Big Bang theories. Alan Guth, Andrei Linde and Steinhardt originally developed cosmic inflation theory to explain some problems with the Big Bang model, and it involved an exponential but rapid expansion of our universe. The cause of cosmic inflation still remains somewhat vague, but for eternal inflation, Guth proposed in 2007 the existence of a ‘false vacuum’ or region of space with a positive energy density – similar to expanding bubbles forming in a boiling liquid. In this manner, certain regions of space-time (or ‘universes’) would be affected by their own form of cosmic inflation, before the positive vacuum moved on to another region. As of yet, this scenario lacks evidence, but if true, then our universe could exist as a nodule on another universe as part of a ‘multiverse’.
BACKED BY
Professor Alan Guth
Another theory suggests that our universe is one of many that exist parallel to one another and is part of a multiverse
Massachusetts Institute of Technology
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Space Science
One theory states that our universe came from a black hole
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What happened before the Big Bang?
NASA’s WMAP was launched to measure CMB fluctuations
“The Big Bang picture is too firmly grounded in data from every area to be proven invalid in its general features” Cyclic models like CCC remain controversial and the Big Bang theory itself still has support. Physicist Lawrence Krauss wrote in 2012, “The Big Bang picture is too firmly grounded in data from every area to be proven invalid in its general features.” So could it be the true picture of the universe after all? Nikodem Popławski, a physicist at the University of New Haven, Connecticut, has developed a theory stating our universe originated from a black hole. Such extraordinary hypotheses have been a topic of speculation for years. Popławski says, “Our universe should obey the same laws as the parent universe in which the black hole exists.” He adds that it should be possible to determine the size of the parent black hole by measuring temperature fluctuations in the CMB. “I published a paper that shows consistency (of the black hole scenario) with Planck’s observations of the CMB. It also shows they aren’t too sensitive to the black hole’s initial size,” he says.
And Popławski is now working on finding evidence for a black hole origin scenario. “If our universe was formed by a ‘big bounce’ in a black hole, then its early expansion has specific dynamics that can be tested by measuring temperature fluctuations in the CMB from all directions in the sky,” he says. Intriguingly, predictions that Popławski and his colleague Shantanu Desai of Garching, Germany, made of CMB fluctuations are consistent with the latest Planck data. And black holes rotate, so if our universe really was birthed from one, Popławski expects to see those effects, too. Finally, echoing cosmologist Stephen Hawking, he says, “Our universe could be the interior of a black hole existing in another universe. Black holes forming from stars and galaxies in such a universe create new universes. And so a universe can parent billions of baby universes, which are formed through black holes.”
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@ Tobias Roetsch; Alamy; Getty Images; NASA; JPL-Caltech; ESA
WMAP and Planck and also the BOOMERanG (Balloon Observations of Millimetric Extragalactic Radiation and Geophysics) experiment, Penrose and Gurzadyan published results that purported to show extremely faint concentric rings from previous cosmic cycles in the CMB fluctuations – similar to ripples spreading outwards when you throw a stone into a pond. According to CCC, what we think of as the universe (the region that we can observe, anyway) is simply an ‘aeon’ – or domain – within an infinitely larger space-time. Eventually, far into the future, once all the stars and galaxies have died out, all matter has dispersed and the supermassive black holes (that lay at the centres of galaxies) have evaporated, our aeon will have become completely smooth. But it will continue to expand and birth a new, larger-scale aeon. The CCC theory (which unlike previous cyclic models has no contraction phases) states that what we think of as inflation is simply the accelerating expansion of a previous aeon. Other cosmologists looking for concentric rings in the CMB haven’t found anything significant yet. This may be because they used standard simulations to check against, whereas Penrose and Gurzadyan adopted a nonstandard approach.
Space Science
THE FORCE TEARING SPACE APART
DARK ENERGY It's the most mystifying phenomenon in the universe, but we’re hot on its trail
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© Shutterstock
Space Science
RS Puppis is an example of a Cepheid variable star. These were essential in showing an expanding universe due to their luminositypulsation period relationship
“Dark energy was discovered by looking at the light of exploding stars in faraway galaxies”
Our universe is growing. Ever since the Big Bang, every point in the fabric of space has been expanding in all directions. This expansion is carrying almost all of the galaxies away from us. The biggest surprise, however, came in 1998 with the discovery that not only is the universe expanding, but that expansion is accelerating. Nobody knows why, but scientists have come up with a term for the mysterious force that is driving the acceleration. They call it ‘dark energy’. According to data from the European Space Agency’s (ESA’s) Planck spacecraft, dark energy constitutes over two-thirds of all the mass and energy in the universe – that’s 68.3 per cent. (And in case you were wondering, the remainder is 26.8 per cent dark matter and just 4.9 per cent is normal matter, which makes up the stars, galaxies and planets.) Worse still, scientists are perplexed as to what dark energy actually is. There are ideas, but nothing concrete. It is important to try and figure out the puzzle of dark energy because the fate of the universe depends on it. Prior to the discovery of dark energy, cosmologists had expected to find that the expansion of the universe should be running out of steam, 13.8 billion years after the Big Bang. If that was the case, the universe could have gone in three directions depending upon how much matter, and therefore gravity, there was in the universe. If there was enough matter, then its gravity would act on the expanding universe, slowing the expansion and gradually overcoming it, eventually causing the universe to begin to shrink again before collapsing in a ‘Big Crunch’. If the amount of matter and gravity were finely balanced with the energy of the expanding universe, it would create a static universe that would remain forever.
What is dark energy? All About Space asks the astrophysicists
“Dark energy makes up about 70 per cent of the universe. It seems to be evenly spread throughout. What we have discovered about dark energy is that it ‘pushes’, as in it repels outwards. It makes the entire universe – which is already expanding – expand faster.”
“Dark energy is incredibly strange, but actually it makes sense to me that it went unnoticed. I have absolutely no clue what dark energy is. Dark energy appears strong enough to push the entire universe – yet its source is unknown, its location is unknown and its physics are highly speculative.”
Dr Karl Kruszelnicki University of Sydney
Dr Adam Riess Johns Hopkins University
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“It could pull the universe apart. If there’s sufficient dark energy, the universe will – at some point – pull itself apart completely in a ‘Big Rip’. The only problem is that we have no clue what dark energy is.”
Dr Hitoshi Murayama University of California, Berkeley
Dark energy
However, if there was not enough matter in the universe to counteract the expansion, then the universe would continue to expand forever, taking all the galaxies with it until they disappeared over the cosmic horizon, leaving the Milky Way Galaxy all alone. With the discovery of dark energy, the fate of the universe now seems much clearer. If dark energy keeps its strength and continues accelerating the universe’s expansion, then it is more likely to expand forever. In the worst-case scenario, the expansion could be so extreme that it begins to tear galaxies, stars, planets and even atoms apart. However, the trouble is, since we don’t know what dark energy actually is, we cannot predict what it is going to do in the future. Astronomers can, however, measure what it is doing today and what it has done in the past, and are able to make some extrapolations based on that. Dark energy was discovered by looking at the light of exploding stars in faraway galaxies. In particular, astronomers were looking at a particular breed of supernovae known as Type Ia. These are
“Just this year, scientists discovered that the universe is expanding faster than we originally thought” the explosions of white dwarf stars and they tend to all explode with the same peak brightness. Of course, from our viewpoint, millions if not billions of light years away from these supernovae, they appear pretty faint. But because we know how bright they would be if we were up close to them, we can calculate how far away they are. Astronomers call these ‘standard candles’ and use them to measure distances across the universe. These distances are then compared to their cosmological redshift, which is the amount their light is stretched into redder wavelengths by the expansion of the universe. It was the fact that the distances to these supernovae were greater than their redshift that implied that the expansion was getting faster, not
slower, as identified by two teams of scientists: the Supernova Cosmology Project led by Saul Perlmutter of the Lawrence Berkeley National Laboratory, and the High-Z Supernova Search Team (Z is astronomy shorthand for redshift) led by Harvard University’s Brian Schmidt and Dr Adam Riess of the Johns Hopkins University. So supernovae continue to be used to measure dark energy. Just this year, Riess led a team of scientists who used Type Ia supernovae to discover that the expansion of the universe is even faster than previously thought. They searched for supernovae in galaxies in which they could also see a special type of variable star, called Cepheid variables. These pulsating stars are also standard candles as their maximum luminosity depends on
An extraordinary example of gravitational lensing in galaxy cluster Abell 2218, due to dark matter. There’s not enough visible matter to distort the light from background galaxies
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Dark energy vs dark matter It’s entirely invisible and neither emits or absorbs heat, light or radiation of any kind.
It can be detected indirectly by its gravitational effect on normal matter and space-time.
It comprises 84.54 per cent of all matter in the universe, or 26.8 per cent of the universe’s total makeup
It plays a crucial role in galaxy formation and stops galaxies from flying apart.
DARK MATTER Galaxies are pulled together by dark matter
The Big Bang 13.8 billion years ago
DARK ENERGY It is accelerating the expansion of space, shown by studies of supernovae in distant galaxies. 148
It exerts a small, negative pressure that’s constant throughout space and acts against gravity.
It was first discovered in the late 1990s by astronomers.
It affects the shape of the universe and its large-scale structure, such as how galaxies and quasars are spread out.
© Tobias Roetsch
Universe is pushed apart by dark energy
Dark energy
the length of their variation – the longer it takes for them to reach peak brightness and then fade back down to normal levels as they pulse, the brighter their peak brightness will be. Comparing the Cepheid data with the distance of those galaxies as measured by Type Ia supernovae, Riess’s team were able to calibrate the supernova distance markers, allowing them to more accurately measure the distances to even more remote galaxies. While the Planck spacecraft had measured the expansion rate of the universe as being 66.5 kilometres (41.3 miles) per second per megaparsec (a megaparsec is equal to 3.26 million light years), Riess’ team found that actually the universe was expanding much faster, at 73.2 kilometres (45.5 miles) per second per megaparsec. That doesn’t mean that Planck made a mistake. The rate of expansion that it measured – which is known as the Hubble ‘constant’ – was from the very beginning of the universe, observed in the light of the Cosmic Microwave Background radiation just 380,000 years after the Big Bang. On the other hand, Riess’ team measured the Hubble constant in the modern universe. It isn’t clear why the two values are different, but one explanation could be that dark energy has grown stronger over the years, speeding up the expansion, meaning that the Hubble constant isn’t actually constant at all. If that is true, then it has serious implications for the fate of the universe. “If we know the initial amounts of stuff in the universe, such as dark energy and dark matter, and we have the physics correct, then you can go from a measurement at the time shortly after the Big Bang and use that to predict how fast the universe should be expanding today,” says Riess. “However, if this discrepancy holds up, it appears we may not have the right understanding, and it changes how big the Hubble constant should be today.” Riess’ findings also somewhat contradict another recent dark energy discovery made by scientists who used NASA’s Chandra X-ray Observatory to observe galaxy clusters. Because galaxy clusters are filled with gas as hot as 1 million degrees Celsius (1.8 million degrees Fahrenheit) or more, they glow brightly in X-rays. These X-ray-emitting regions of galaxy clusters all have similar shapes and sizes relative to the size of the clusters themselves. “In this sense, galaxy clusters are like Russian dolls, with smaller ones having a similar shape to the larger ones,” comments Andrea Morandi of the University of Alabama, Huntsville, US, who led the team. “Knowing this lets us compare them and accurately determine their distances across billions of light years.” From these distances, the true size of the clusters can be gauged. Because the growth of galaxy clusters is ultimately stunted by dark energy pulling away galaxies that would otherwise join the clusters, how big galaxy clusters can reach during different epochs of history is an indication of how strong dark energy is and how it has acted over billions of years. Since a galaxy cluster’s X-ray profile is a proxy for its true physical size, by measuring them with Chandra, Morandi’s team found that dark energy doesn’t seem to have become stronger or weaker in the last 8.7 billion years. This might mean that a change in the
The Dark Energy Survey, an international effort based at the Cerro Tololo Observatory, Chile, began searching the southern skies on 31 August 2013
The Dark Energy Survey (DES) will map millions of galaxies and probe the origin of the accelerating universe
DES will carry out a deep, wide-area survey over 525 nights to record information from 300mn galaxies
More than 400 scientists from over 25 institutions across the world are working on the DES project
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Space Science
An artist’s impression of the Planck spacecraft cruising at the L2 point
Dr Adam Riess of the Johns Hopkins University and his High-Z Supernova Team published some of the first evidence that the expansion of the universe is accelerating
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expansion rate of the universe occurred before then, closer to the time of the Big Bang. Galaxies can also reveal the presence of dark energy in other ways. We’ve seen standard candles in the form of supernovae, so now meet ‘standard rulers’, which are physical yardsticks that we can measure dark energy against. The distribution of galaxies in the universe can be traced back to perturbations seen in the cosmic microwave background, which resulted in a standard distance between galaxies. This standard distance can act like a ruler and, by measuring how the distance between galaxies has grown as the universe has expanded, astronomers can measure the strength of dark energy. However, for standard candles and standard rulers to really make a difference in our quest to solve the mystery of dark energy, what scientists really need is much more data. This data will come from giant galaxy surveys, conducted by both general-purpose observatories and dedicated dark energy projects. First up is the Dark Energy Survey, which is an international project to detect many thousands of Type Ia supernovae, but which also aims to map out the large scale structure of the universe in the form of hundreds of millions of galaxies, providing many more examples of standard rulers. The Dark Energy Survey began in 2013 and it uses the four-metre (13-foot) Blanco telescope and its powerful 570-megapixel Dark Energy Camera at the Cerro Tololo Inter-American Observatory, situated in Chile. The project released its first batch of data for scientists to begin analysing in January 2016, and the survey will continue to run until 2018. “Thanks to the extreme sensitivity of the camera and to the large area of sky that can be imaged through the telescope at once – 15 times the size of the full Moon – we expect the Dark Energy Survey to find more supernovae than any previous experiment,” comments Dr Chris D’Andrea of the University of Portsmouth, UK. In the first few months alone, it found 200 Type Ia supernovae. However, we’re still a few years away from having a thorough analysis of the results. Meanwhile, there will be an American rival to the Dark Energy
“Dark energy appears strong enough to push the entire universe – yet its source is unknown, its location is unknown and its physics are highly speculative” Dr Adam Riess
Dark energy
Dark energy and the future of the universe There are several possible scenarios for the fate of the cosmos, but only time will tell which will prevail – and dark force is partly responsible SCENARIO 1 Expanding forever: dark energy is the same everywhere NOW In this scenario, there’s not enough gravitation to stop or slow the expansion of space. In an ever-expanding cosmos, dark energy has the same strength everywhere.
FUTURE
Dark energy originates from space itself
The universe continues to expand as it has been doing so; accelerating, but not so much that anything drastic happens. Stars and galaxies continue to evolve indefinitely and for an infinite amount of time.
Universe expands forever
Matter clumps together The Big Bang
SCENARIO 2 Big Crunch or Big Rip: dark energy alters its strength NOW Many cosmologists think that dark energy could have different strengths in different parts of the universe. Having a varying ‘concentrate’ of this strange force means that there’s a continual of repulsion, even when the cosmos is expanding. A change in dark energy’s strength could explain how large galaxy clusters are made.
FUTURE Dark energy’s strength changes as the universe expands
Variable dark energy leads to two possibilities: it continues to dominate, leading to ever-faster expansion where galaxies, stars and planets are torn apart in a ‘Big Rip’, or dark energy weakens, causing gravity to dominate. Eventually the expansion of the universe slows so much that the cosmos ends in a 'Big Crunch'.
Option 1: Universe is torn apart If dark energy dominates, the cosmos will end in a ‘Big Rip’.
Option 2: Universe collapses in on itself If dark energy weakens, then the cosmos will end in a big crunch.
SCENARIO 3 An illusion: dark energy isn’t real NOW The final scenario is that dark energy doesn’t exist in the way we think and that it is in fact a huge illusion. Modifications of general relativity can explain distant supernovae and galactic redshift observations without the need for dark energy, suggesting a fundamental flaw in our understanding of gravity.
Just as general relativity intended Just as predicted by relativity, galaxies, galaxy clusters and gravity act as normal.
Getting the bigger picture Looking at the scale of the cosmos as a whole, gravity is found to ‘disobey’ general relativity as the universe appears to accelerate.
FUTURE In the case where dark energy or the cosmological constant doesn’t exist, we may need to re-evaluate how gravity works on different scales. On galactic scales it may be attractive and may act like dark matter, but on larger scales it may continue to cause expansion.
An uncertain future Until we understand fully how gravity behaves on large scales, the future of the cosmos is anyone’s guess.
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The evidence for dark energy
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The relic radiation that fills space
The cosmic microwave background (CMB) is the distant, primordial microwave ‘echo’ of the universe. Measurements of the CMB taken by space probes show that the universe’s geometry is nearly flat. For that to be the case, the total amount of matter in space must tally with the average density of matter to energy in the cosmos. But measurements of the CMB spectrum show that this isn’t what’s happening – matter only accounts for 30 per cent of the density. Something is missing.
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Exploding stars
A Type Ia supernova occurs in binary systems when a white dwarf’s gravity pulls material from the other orbiting star onto itself, causing it to explode, briefly outshining all other stars in its galaxy. This means they are visible across the cosmos. Their intrinsic brightness is also known, so their distances can be calculated from how dim they appear. Using this method, scientists were able to show that the universe’s expansion is accelerating.
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The shape of the cosmos
The shape of the universe is governed by the general theory of relativity, which describes how space-time is warped by matter. Measurements of the CMB radiation show that the universe is nearly flat, except that there’s not enough matter to keep it that way. Since E=mc2 shows that matter and energy are two sides of the same coin, could dark energy remedy the shortfall as the intrinsic energy of space?
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The universe is expanding
The expansion rate of the universe is the time it takes to expand a certain amount. In a certain period of time, space will expand by a certain amount and whatever makes space expand doesn’t dilute or decrease in density. An expanding universe leads to a greater amount of space, and more of what caused the expansion. This suggests that dark energy may be a feature of space itself.
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Survey, named the Dark Energy Spectroscopic Instrument, or DESI for short. It’s destined for the four-metre (13-foot) Mayall telescope at the Kitt Peak National Observatory in Arizona, and will measure the cosmological redshifts of 30 million galaxies out to a distance of 10 billion light years in order to create a huge map of the large-scale structure in the universe. It will look at how the expansion of the universe has stretched the space between individual galaxies, as well as the size of galaxy clusters. Unfortunately, it doesn’t start work until 2018, just as the Dark Energy Survey is completing its work, so we will have to wait a while for its results, but it will build on the efforts of previous surveys such as BOSS, the Baryon Oscillation Spectroscopic Survey, which was part of the Sloan Digital Sky Survey based in New Mexico. This measured the redshifts of a million galaxies across 6 billion light years and allowed comparisons to be made of the growth of standard rulers between the modern day and 6 billion years ago. It’s an even longer time frame for other projects. The most powerful digital camera in the world, featuring 3.2 billion pixels, will be fitted to the heart of the Large Synoptic Survey Telescope (LSST) – a huge 8.4-metre (27.6-foot) telescope that is under construction on a mountain called Cerro Pachon in Chile. While it will be a general-purpose survey telescope, the LSST will map millions of galaxies and find many more supernovae to aid in the quest to learn more about dark energy. But there are more ways to study dark energy than just with visible light. The Square Kilometre Array, a vast interconnected network of thousands of small radio telescopes that will come online in the next decade, will study dark energy in two ways. First, it will listen for how the gravity of galaxy clusters affects the passage of radio waves through the universe, with the size of the radio distortion being a signal to indicate the different size of standard rulers across billions of years. It will also complete a survey of galaxies via the 21-centimetre (8.3-inch) wavelength radio emissions from neutral hydrogen in those galaxies, adding to the many galaxies observed by other surveys to help create a comprehensive map of the universe from which we will be able to measure dark energy across space and time. Finally, the quest for dark energy will be quite literally heading into space with the joint ESA/ NASA Euclid mission, which is set to launch in 2020. Armed with a 1.2-metre (3.9-foot) telescope, which is a decent size for a space mission, and a 600-megapixel digital camera, it will map the size and location of a whopping 2 billion galaxies, more than have ever been mapped before, across 10 billion light years. It will tell the story of the evolution of the standard rulers in the universe, as well as highlight the result of the battles between gravity and dark energy in the growth of galaxy clusters. “Euclid will provide a wealth of data on the threedimensional matter distribution in the universe,” says Ralf Bender of the Max Planck Institute for Extraterrestrial Physics in Germany, who is a scientist working on the Euclid mission. “Not only will this give us interesting insights into the evolution of galaxies and galaxy clusters, but we will
Dark energy
also be able to better understand the accelerating expansion of the universe. Hopefully, this will bring us a big step forward in solving the riddle that is dark energy.” Of course, the solution to that riddle is the 64 million dollar question. Although nobody knows exactly what dark energy is, scientists’ best guess is that it is one of two types of phenomenon. The first idea is that it is something called quintessence, which is a type of energy field that varies across space-time. Adam Riess’ measurement of a modernday expansion rate of the universe, that is at odds with the expansion rate not long after the Big Bang, may be evidence that the quintessence model is the correct one. On the other hand, an alternative model is described as the Cosmological Constant, which is
a constant energy field that has the same strength at all points in space and time. If dark energy is the Cosmological Constant, it would mean that either Riess’ measurement of the expansion, or Planck’s data, is somehow in error or being misinterpreted. Quintessence and the Cosmological Constant are fairly vague descriptions, however. What exactly dark energy is, how it arises, and where this mysterious force gains its strength from are still open questions, but for scientists working to figure it out, there’s a big prize awaiting them. Riess, Schmidt and Perlmutter won the Nobel Prize for Physics just for discovering dark energy. The scientists that finally solve the mystery won’t just win the Nobel Prize – they could well be the first scientists to conclusively declare what the fate of the universe will be.
Various instruments, such as DASI (pictured here), helped corroborate WMAP’s findings that our universe is nearly flat
“Dark energy has grown stronger over the years, speeding up the expansion, meaning that the Hubble constant isn’t actually constant at all”
An image of a galaxy cluster, with hot intracluster gas shown in pink. The blue overlay reveals the calculated areas of dark matter
An artist’s impression of all four elements of the Square Kilometre Array dishes at night
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Space Science
Dark energy mappers A new generation of instruments promises to hunt down dark energy, exposing its darkest secrets
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21
The wavelength, in centimetres, of the hydrogen radio emissions that SKA will observe
1 million
The multiple of today’s entire internet traffic that SKA’s aperture arrays could produce
The approximate number of antennae in the SKA network
8.4 million The number of today’s latest smartphones that SKA’s data would fill in a single day
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The total number of megapixels in DECam’s sensor
Individual scientists from the US, Spain, the UK, Brazil, Germany, Switzerland and Australia are working on DES
The weight of the largest of DECam’s five lenses
300 million SKA’s total collecting area in square kilometres
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tennis courts
Equivalent to:
43 smartphone cameras
-100
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over
This is a visible and near-infrared survey of the universe using the four-metre (13-foot) Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile. The telescope has been fitted with the state-of-the-art, robotic Dark Energy Camera (DECam), which will survey 300 million extremely faint galaxies and thousands of supernovae over an eighth of the total sky. The DECam instrument will make repeated observations of certain areas of the sky in various wavelengths, as well as more longperiod observations to pick out the faintest galaxies. In this way, the DES project hopes to discover if dark energy’s density changes over time.
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Dark Energy Survey (DES)
The temperature, in degrees Celsius, to which DECam’s 74 CCDs must be cooled
The number of faint galaxies that the survey will record using the Dark Energy Camera
Square Kilometre Array The Square Kilometre Array (SKA) will span two continents when it begins operation in 2020. As the largest radio telescope network in history, all of SKA’s individual elements will be able to act like a single, super-continental radio dish, giving it the ability to study the universe in resolutions never before seen in radio wavelengths. In particular, emissions from hydrogen gas – the most abundant element in space – will be mapped in three dimensions from the distant past to the present day. SKA’s high resolving power could reveal dark energy’s effects from ripples in the gas and more information on galactic evolution.
Euclid space telescope How has dark energy contributed to the universe’s acceleration over cosmic time? This is what ESA’s Euclid spacecraft will try to ascertain when it is launched in 2020. It will do this by measuring the redshifts of galaxies back to when the universe was just 28 per cent of its current age. It will also look at gravitational weak lensing, as well as ripples in normal matter (usually in hydrogen gas between galaxies). To get decent results, Euclid will survey at least half the entire sky with its visible and near-infrared cameras.
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The number of gigabits of compressed data that Euclid will collect per day
10 billion
© NASA; ESA; Hubble Heritage Team; Johan Richard (Caltech, USA); Reidar Hahn; D. Ducros; LFI & HFI Consortia; Lloyd DeGrane; University of Chicago; ESO; CXC; D. Coe (STScI); J. Merten (Heidelberg/Bologna); SKA Organisation
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The total area of the sky that Euclid will observe during its 6.5-year mission life
© Adrian Mann
Dark energy
The number of years into the universe’s past that Euclid will look into
1.2 Diameter of Euclid’s Korsch telescope mirror, in metres
1.5 million Euclid’s distance, in kilometres, from Earth in its operational orbit
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Future Tech See how we're planning to explore and expand into space 158 Next-generation space planes Welcome aboard your future ride into space
166 Droids on another world How NASA is making robots a reality
168 Interstellar travel Turn your attention to the stars beyond our Solar System
174 Space elevator Could we take a lift into space and avoid all the hazards?
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Robots investigate planets 156
“We're still a long way off C-3PO, but at least there is now a real humanoid robot helping us in space”
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The future of space travel
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Riding a space elevator
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© Adrian Mann; Alex Pang; Shutterstock
Become a space tourist
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Next-generation
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AAS Spaceline All About Space welco mes you aboard your future ride into space
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SPACE TRAVELLER From
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Flight Information Scheduled launch:
2016
2017
2018
2025
Lynx
SpaceShipTwo
Dream Chaser
Skylon
XCOR Aerospace
Virgin Galactic
Sierra Nevada Corporation
Reaction Engines
This winged, suborbital spacecraft is a horizontal take off and horizontal landing craft that is able to carry one pilot, one passenger and/or a payload up to 100km (62mi) altitude. According to latest 2015 reports on the project, the Lynx space plane is due to take its first flight in 2016.
SpaceShipTwo is an air-launched rocket plane designed to carry six people on space tourism flights. It is carried up to 15km (9.3mi) altitude by its specially developed carrier aircraft White Knight Two, where it drops off and uses its rocket to boost up to a maximum height of 110km (68.4mi).
Dream Chaser is a lifting body space plane, where the wings and the body blend into one shape. It will be vertically launched into orbit on top of an Atlas 5, or possibly an Ariane 5 rocket. It would then be able to rendezvous with the Space Station, before returning to land on a runway.
The Skylon’s engines will be able to draw in oxygen from the atmosphere from take off, reducing the weight of the aircraft. This makes it possible to create a single piece vehicle that can take off from a runway, fly into orbit, and then return to the same runway, much like an aeroplane.
Cost of seat: 95) 100,6 $150,000 (£
Cost of seat: 00) (£165,2 $250,000
Cost of seat: $TBC
Cost of seat: 38) 275,4 $417,000 (£
Capacity: 2
Capacity: 8
Capacity: 7
Capacity: 30
Mass: 5,000kg
Mass: 11,300 kg
Mass: 9,740 kg
Mass: 275,000kg
Speed: 1.03km/s (0.64mi/s)
Speed:
At the peak of the space race in 1968, Stanley Kubrick’s 2001: A Space Odyssey gave life to the space future that many people expected lay ahead. The story began with a Pan-Am Orion III space plane carrying passengers to a giant rotating space station in Earth orbit. It’s a sleek, white, delta-winged craft that looks like a cross between Concorde and the Space Shuttle, and provides airline-like travel directly into Earth orbit. Of course, space travel did not continue to develop at the same rate, and even the Space Shuttle failed to deliver cheap routine access to space, let alone in-flight entertainment and steward refreshment services. Now, however, a new generation of projects are bringing the space plane from the pages of science fiction and into reality, and these projects may pave the way for the future of space tourism. One of the first new space planes to take to the skies is Virgin Galactic’s SpaceShipTwo (SS2), developed from the smaller SpaceShipOne (SS1) that
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Speed:
1.3km/s (0.8mi/s)
Speed: 8km/s (4.8mi/s)
flew in 2004 to win the $10 million (£6.6 million) Ansari X Prize for private human spaceflight. SS1 and SS2 are suborbital space planes, which means they can reach the 100-kilometre (62-mile) high boundary of space, without going into orbit. They both use hybrid rocket engines, burning solid rubber fuel with nitrous oxide as an oxidiser, while most spacecraft use two liquid propellants, and missiles typically have solid rocket motors where the fuel and oxidiser are mixed in one solid block. But, despite their novel propulsion, it is their re-entry system that is unique. To safely re-enter the atmosphere the SpaceShip must return at just the right angle or potentially burn
8km/s (4.8mi/s)
up, and Scaled Composites’ designer Burt Rutan was determined to find a fail-safe way of bringing his new space plane back to Earth. And he found it with the SS1’s “feathering booms”. The craft has twin tails sticking out of its square wing and once it reaches space it folds these up, so that the tailplanes and the back half of the wing are at a right angle to the body. This forms a stable shape that ensures the craft always falls the right way back into the atmosphere, without the pilot having to do anything! Once back in the atmosphere, it folds its tail down again and lands normally on a runway. Though the SS1 only made three spaceflights before it was put on
“A new generation of projects are bringing the space plane from the pages of science fiction and into reality”
Next-generation space planes
A SNC technician inspects the interior cabin of the Dream Chaser space plane
“We took a significant but considered gamble to develop a vehicle that could replace the Shuttle” Mark Sirangelo, Sierra Nevada Corp. display at the US National Air and Space Museum, Virgin Group licenced the technology and established Virgin Galactic (VG) with the intention of offering space tourist flights from as early as 2007. Scaled Composites began designing the SS2 for VG, a larger and updated version that carries six passengers and two crew members using the same hybrid propulsion and feathering re-entry. You can buy tickets right now, if you have $250,000 (£165,200) to spare, which will get you just four minutes in space and three days space training in the lead up to your flight – at least that is the plan. But, scaling up the technology from the five-metre (16.4-foot) long, 3.6-ton SpaceShipOne to meet the needs of the 18 metre (59 foot) long and 9.7-ton SpaceShipTwo has been much more challenging than originally expected. Hybrid engines have safety and simplicity advantages over bi-liquid rocket engines, but they are very tricky to get right; and the SS2’s bigger engine has suffered rough burning and less
XCOR Aerospace’s suborbital spacecraft, Lynx, during its construction
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Departures Your trip into space Virgin Galactic hope to be the first to offer trips into space, and they have already planned the experience… Getting ready for your space flight will be a little different to other airports. Virgin Galactic will operate from Spaceport America in New Mexico, where they have built a dedicated terminal building. When you arrive at the Spaceport, the first process will involve health checks; SpaceShipTwo is designed to allow as many people as possible to be able to access space, but basic physical condition of passengers will need to be tested. Next there are three days of training. This will involve mock-ups
and simulations of the cabin and flight sequence – a bit more extensive than your standard flight safety demonstration on board an aeroplane! Your flight will take off at dawn, slowly circling up attached to the carrier aircraft, White Knight Two. The Sun will rise as you reach 15 kilometres (9.3 miles) altitude, where you will drop off the White Knight Two, fire the engine and pull up nearly vertical for a minute, as the engine roars and the sky turns black. Weightlessness will commence
Reaching space
Coastal or desert location
Space is only 100km (62mi) away. Straight up, suborbital space planes will just reach this altitude before falling back to Earth, whereas orbital space planes must achieve a speed of 29,000km/h (18,020mph) in order to get into orbit.
Rocket vehicles will always remain more risky than aeroplanes because of the larger amount of energy packed into them. All the prospect spaceports are located in remote areas to ensure safer spaceflights.
Two-stage space plane Virgin Galactic’s launch system is a two-stage space plane, where a small rocket plane is carried on a larger carrier aircraft, the White Knight Two.
Different operators It is hoped that a number of commercial systems will all become available and we will see a diverse variety of space vehicles at the spaceports.
Runway Space planes need a runway as they are designed to make horizontal landings. SpaceShipTwo and Skylon would both be making horizontal take offs, too.
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when the engine cuts, as craft and crew are all now coasting up past 100 kilometres (62 miles) altitude at the same rate. You’ll see the Earth spread out below and the curving black horizon, while experiencing around four minutes of weightlessness before the atmosphere starts to build up again on the way back down to Earth. After a gentle 1.5 G re-entry, you will glide down for a runway landing and an après-space party with your fellow passengers.
Next-generation space planes
Passport Control Spaceports of the world
6 5
1 Mojave, California Where VG are currently developing SpaceShipTwo.
2 Spaceport America, New Mexico Where VG will operate commercially.
3 Cape Canaveral, Florida Where Dream Chaser will likely be launching on Atlas rockets.
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4 Kourou, French Guiana
2
Where Skylon might start operations. The equatorial location will give best orbital performance, and liquid hydrogen and oxygen are already made onsite.
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5 Machrihanish, Scotland On the Mull of Kintyre, Scotland, this is the leading candidate for the UK spaceport. VG have expressed interest.
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6 Kiruna, Sweden VG have considered launching SS2 from here to explore the Aurora Borealis.
Terminal building Certainly for the near future, space flight will either be a business need or a luxury. Virgin Galactic have designed their terminal at Spaceport America to be a prestigious centre of operations for wealthy clients.
Vertical launch SNC’s Dream Chaser is to be launched vertically on a traditional rocket, in their case likely to be launched from Cape Canaveral, and returning to a runway near the launch pad.
Special propellants Rocket engines need both fuel and a source of oxygen. New spaceports will have to provide a range of these for different spacecrafts, including hydrogen, oxygen, nitrous oxide and hydrogen peroxide, as well as jet fuel.
performance than intended. It seems that planning to offer space tourist flights in 2007 was a little ambitious, as it was to be another six years before the SS2 made its first powered flight in 2013. With a run of successful tests behind them, VG launched the SS2 in October 2014 with a new engine that burned nylon fuel. If it was successful, commercial space flights were expected to begin in 2015. Shortly after dropping off its carrier aircraft and igniting its engine, the SS2 was seen to break apart in flight. While many immediately assumed a fault with the new engine, the air crash investigation found the copilot, under the stress and vibration of live firing, had unlocked the tailbooms too early. Without the locks in place and as the SS2 went supersonic, the aerodynamic forces on the tail overwhelmed the mechanism and folded the craft in half. The investigation vindicated the engine, and the SS2’s overall design, and VG have a brand new space plane ready to begin test flights in 2016. The original and simpler, rubber fuelled engine has improved and the tails have a new locking system to prevent early release. Even with these advancements, VG are not putting a timescale on when commercial spaceflights will begin, though it seems likely that it will be over ten years later than originally planned. But, better late than never. Though the SS2 will hopefully be carrying humans to space soon, it still can’t reach orbit, which requires a horizontal speed of 29 kilometres (18 miles) per second while in space. But there is one company who are working on a new generation of space plane that could reach this speed: Sierra Nevada Corporation (SNC) based in Louisville, Colorado. A long established supplier of aerospace hardware, SNC took on the Dream Chaser project when it bought a company called SpaceDev, realising the ageing Shuttle programme might present an opportunity. “We took a significant but considered gamble to develop a vehicle that could replace the Shuttle,” says Mark Sirangelo, the corporate vice president of
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Flight Connections space systems at SNC. “We took a blank sheet and considered how we would build the Shuttle in light of new technology and the Shuttle’s operational experience. So, Dream Chaser is designed to carry the same amount of people and critical supplies as the Shuttle, but without the heavy cargo; it is about transport, not deployment.” While investigating potential concepts, SpaceDev found a cancelled NASA lifting body programme from the 1990s called HL-20 that had been intended as a space station lifeboat. A lifting body is a craft where the shape of the fuselage creates lift, rather than having separate wings, and HL-20 was based on NASA research that stretched as far back as the 1960s. NASA granted SpaceDev permission to revive the HL-20 and develop it further, establishing the Dream Chaser’s core design. SNC is pursuing Dream Chaser for a number of markets including state and commercial crew transport and free-flying research missions, both crewed and autonomous. But the immediate focus
of the project is in producing an autonomous cargo transport craft for NASA’s latest Space Station Commercial Resupply Services competition (CRS2). “The CRS2 version has folding wings so it can be launched in a standard payload fairing that is used by both Atlas V and Ariane 5,” says Sirangelo. “Also, whether we’re flying people, or cargo, or lab experiments, we can bring Dream Chaser back to any runway that can take an Airbus A320. Our propulsion systems are nontoxic so the vehicle can be accessed immediately, and it can fit in a normal transport aircraft for return home.” With features that minimise cost and maximise
convenience, SNC are confident about Dream Chaser’s future and an atmospheric test version is ready for flight testing in early 2016. SNC are working with Lockheed Martin who are currently assembling the spacecraft cabin at their facility in Fort Worth, Texas, and the first space capable version is expected to reach space in 2018. In the form of Dream Chaser we have a reusable orbital space plane that can carry seven people and land on a runway. However, it still needs to be stacked on top of an expendable rocket to get into space via a vertical launch. But what about the single stage airliner that can take off from a normal airport and fly to space and
“Not only is Skylon cheaper to run but it has been designed with a flexible payload bay that can carry anything”
SNC’s Dream Chaser is a reusable spacecraft that can land on a runway
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Next-generation space planes
Skylon would be able to carry you from London to New York via orbit in just 12 minutes
@ Alex Pang; Sierra Nevada Corporation; UK Space Agency; Reaction Engines; Virgin Galactic; XCor
back in one piece? Well, perhaps unexpectedly, the UK is now home to the leading contender, the wonderfully named Skylon from Reaction Engines Limited (REL) in Oxfordshire. With a sleek, black Concorde-like appearance, Skylon is the leading concept for a single stage to orbit space plane. At a staggering 82 metres (269 feet) in length and weighing 275 tons at launch, the Skylon space plane can carry 12 tons of payload into low-Earth orbit. The key enabling technology for this futuristic space plane is Synergetic Air Breathing Rocket Engine (SABRE), which REL have been developing for the past 25 years. The engine will run on liquid hydrogen and air or oxygen; when starting on the ground and flying within the atmosphere it uses the cold liquid hydrogen to cool down incoming air, which makes it possible to compress it into a rocket engine. Once above the atmosphere SABRE switches to on-board oxygen. This will reduce the amount of oxygen the space plane has to carry on board by 20 per cent, saving enough mass that Skylon can be built as one piece and be reused, just like an aeroplane – and just like the Orion III. After many years of fundamental research, REL are very confident in the potential of their technology. “Our immediate focus is the SABRE, and we are now moving from a research organisation to one involved in the detailed engineering development of the ground test engine,” says Mark Thomas, CEO of REL. “We aim to have that up and running by 2020, with engine-in-flight testing early next decade. The engine itself is airframe agnostic, it could be built into other designs too, and enable a whole new generation of aerospace vehicles.” Because Skylon would fly multiple times like an aeroplane, it would make flying anything to space much cheaper. It’s estimated that its launch would cost ten per cent of a current space launch. And, not only is Skylon cheaper, but it has been designed with a flexible payload bay that can carry anything, including a personnel module, potentially transporting 24 astronauts into space. Flying on Skylon would be a windowless affair, but it would be the most comfortable and the cheapest flight to orbit. With a horizontal runway take off and comparatively gentle acceleration to orbital speed over a longer period of time, once in orbit Skylon would manoeuvre like any other spacecraft, but it has an advantage when it comes to re-entry, too. It is much lighter for its size than any previous spacecraft, which allows it to start aerodynamic braking in thinner air, much higher up. This makes for a cooler and gentler return to Earth. And, once back in the atmosphere, Skylon will glide back to land on a runway – just like the aeroplanes that currently transport us all over the world. But, this craft can get you from London to New York in just 12 minutes! It’s an exciting concept and one that has been gaining support from UK government funding and received positive feedback from the ESA and USAF. But, more importantly, it also opens up wider possibilities for future human exploration missions in our Solar System. Maybe by 2034 (as long after the year 2001 as Kubrick’s 2001: A Space Odyssey was before it) you will finally be able to take a tour of Earth from orbit, or even venture further a field, and they’re sure to add back seat screens so you can enjoy the astonishing views.
Sir Richard Branson, the founder of Virgin Galactic
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Droids on another world From C-3P0 to Robby and K-9, science fiction is full of helpful robots. Now NASA is making it a reality
The word robot comes from the Czech word robota, meaning slave; and it was created for Rossum’s Universal Robots, a play first performed in Prague in 1921. It featured humanoid robots produced to do humanity’s drudgery and their eventual rebellion; it proved a worldwide success and gave us the word and the classic science fiction robot. Robots are now an integral part of most futuristic space fiction, yet reality has both far exceeded expectations and somewhat underwhelmed. Robotic spacecraft have touched down on six different bodies, driven around on the Moon and Mars and reached interstellar space. But classic science fiction humanoid robots have been in short supply. Fortunately, NASA is actually working on making them our new helpers in space. When the International Space Station (ISS) was still in development in the 1990s, the idea of having a humanoid robot to help the astronauts on board was suggested. It may sound fanciful, but if you can build a robot in a human shape it would be a huge advantage in them working with humans, especially in an environment as challenging as space. The working areas of the ISS are designed around, and for, humans, so a robot helper would only be a hindrance if it gets in the way of the astronauts. A successful humanoid robot could work in the station in concert with the astronauts rather than around them; using the same facilities and tools without the need for separate “robot” equipment. This idea has become Robonaut, developed by NASA in conjunction with robotics firm Oceaneering and General Motors. The Robonaut programme is working to build up the capability of these assistants in stages, starting with Robonaut Type 1 in 2000. The Type 1 focused on creating a multi-purpose humanoid torso, arms, and head that could be mounted in different ways. Within the space station it would have a single grappling leg, as in zero gravity
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it wouldn’t need two; outside it might be attached to the end of the station’s robot arm, enabling an astronaut to perform an Extra-Vehicular Activity (EVA) via telepresence, without having to risk going outside themselves. Taking this further, NASA integrated a Type 1 with self-balancing, Segway-like wheels, as well as a more substantial four-wheeled rover, to evaluate the practicality of these robots assisting astronauts on planetary surfaces, particularly the telepresence exploration of remote or dangerous terrain. This resulted in a really menacing looking “Centaur”; a chunky looking torso and arms with a Boba Fett helmet mounted on an elongated neck! Finally, in 2011 a Robonaut made it to the ISS, in this case the rather more friendly looking Type 2. The Type 2 is able to operate faster and more dexterously than its predecessor and can manipulate items up to 20 kilograms (40 pounds). It can be controlled either by astronauts on the space station, or by operators on the ground via telepresence. It features touch sensors in its finger tips among a total of 350 different sensor inputs, and 38 different computer processors around its distributed control system. A major aim for the Robonaut programme is that it can be set to basic repetitive tasks and left to operate autonomously, freeing the astronauts for more important work. This is another area where the humanoid form is an advantage, just as we can turn our hands to many different tasks without specialisation, so can the Robonaut. Robonaut was first powered up on the ISS in August 2011 and has been undergoing gradual development ever since. Exploring initially how the fixed torso could help inside the station, it has now received some legs in anticipation of its own battery pack (enabling free movement) in the near future. We’re still a long way off C-3P0, but at least there is now a real humanoid robot helping us in space.
Wheels Droids will be useful on the terrains of rocky worlds such as the Moon and Mars. Hopefully, some will be used on selfbalancing wheels and a four-wheeled rover.
Droids on another world
“Robonaut 2 can be set to basic repetitive tasks and left to operate autonomously on the ISS, freeing the astronauts for more important work” In-built battery To be truly useful, the Robonaut will need to have its own internal battery, most likely returning to its charging station autonomously.
Stereoscopic cameras Robonaut could be fitted with 3D cameras, this would enable astronauts to explore a planet from a fixed base, or even in orbit.
Torso The main enclosure for the Robonaut systems, this is the basic building block that can be mounted for different tasks.
Human-like arms Robonauts have two arms just like us. The shoulders can twist and rotate as normal, while the hands have 12 degrees of freedom.
Touch sensitive fingers
Legs Future humanoid robots will have two legs to walk dynamically on a range of surfaces. © Adrian Mann
Robonauts are able to manipulate items up to 20kg (40lb) in mass, but to be able to cope with a wider range of tasks they have force-sensing fingers.
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INTERSTELLAR + how to become TRAVEL a space tourist Having explored much of the Solar System, attention is now turning to the stars beyond As the spacecraft approaches the planet, things seem quite familiar. Sunlight glints off an expanse of blue ocean, and white clouds are corralled by gusts of wind. But a closer inspection is jarring – the continents are all in the wrong place. That’s because, for all its similarities, this isn’t the Earth. Instead, we’re looking at the first historic images sent back of another world orbiting a star far beyond the Sun. In days gone by, such ideas were little more than a pipe dream. But the tide, it seems, is turning. Back in April, Stephen Hawking and Russian billionaire Yuri Milner launched their Breakthrough Starshot project to an enthralled press conference. Their goal is to one day fire lasers at sails strapped
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to tiny stamp-sized spacecraft, launching a swarm of explorers to Alpha Centauri – the nearest star system to the Earth. If successful, the journey might only take a few decades. Such interstellar travel is no longer an absurd idea according to Andrew Coates, a space scientist from University College London. “It is not completely pie in the sky,” he says. As things stand, we only have one distant emissary of humankind, one that has departed the planetary system in which we reside. That is Voyager 1 – the probe sent to explore the outer planets in 1977. In 2012, measurements of the solar wind suggested it had left the magnetic influence of the Sun – one way of arguing it has departed the
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Solar System. Yet it is nowhere near the next solar system. That’s the problem with space – it really lives up to its name. A trip to the Alpha Centauri system requires us to travel a staggering 40 trillion kilometres (25 trillion miles, or 4.37 light years). At the speed of Voyager 1 it would take at least 30,000 years to cover that distance. That’s why Hawking and Milner have turned to an alternative solution. Their goal is to take advantage of advances in technology miniaturisation. “We’re already seeing one-tonne spacecraft being scaled down to a one-kilogram [2.2-pound] CubeSat,” says Colin McInnes from the University of Glasgow. “You can imagine a similar device in future weighing a gram [0.03 ounces].” If we can pack the intricate payload of a modern space probe onto a chip the size of your thumbnail,
then we’ll have a really lightweight explorer ready to be dispatched to the stars. However, it wouldn’t be fired by traditional rocket-based propulsion – that’s simply too slow. Instead, the Breakthrough Starshot team proposes firing pulses from a ground-based 100-gigawatt laser at sails strapped to a flotilla of micro-spacecraft. This should give each interplanetary spacecraft an almighty kick, accelerating them up to ten per cent of the speed of light. Send enough and a few survivors should make it to Alpha Centauri within a human lifetime. The onboard cameras could then send back those historic images of a distant alien solar system. If it sounds simple, it isn’t. “There are a number of engineering problems to solve,” says Coates. Not least developing the 100-gigawatt laser required. There are safety concerns, too. “You’d have to worry about what
“In 100 years’ time, human hibernation may be possible, making it easier to send humans to the stars” Ian Crawford
Physicist Stephen Hawking has thrown his name behind the Breakthrough Starshot mission to get to Alpha Centauri
a laser of that power would do to the atmosphere, or to aircraft or satellites orbiting above,” says Coates. But McInnes believes there will come a time when technology converges and it will become feasible. “We could well see with interstellar travel that someone puts advancing technology together in a novel way to create something new,” he says. Doing so would also bring us greater knowledge of the environment between the stars – the interstellar medium – and kick-start a revolution in our understanding of this under-explored region of space. Yet for many, the real dream of interstellar travel is not to dispatch tiny robots, but instead to send people to explore these far-off solar systems, just as early terrestrial explorers sailed vast oceans to conquer new continents. “There is no doubt that humans are more efficient explorers than robots,” says Ian Crawford, a planetary scientist from Birkbeck, University of London. Yet we are currently about as far from travelling between the stars as you can get. We’ve barely dipped our toes into the vast cosmic waters and instead we remain largely in lowEarth orbit with only a dozen American men having left their footprints in the lunar dust. As we’ve seen, the distances involved in interstellar travel are more than intimidating. If we are to cover them within a human lifetime, then we need to be able to accelerate people to at least ten per cent of the speed of light – something that brings with it a whole host of new challenges. “The real limiting factor is mass,” says Crawford. The trouble with human missions is that we need food, water and oxygen to survive. Providing all of these things significantly ramps up the mass of the mission. To accelerate that mass you need fuel, which itself adds mass, requiring even more fuel. It’s a vicious circle. “It becomes such a difficult problem that it would be irresponsible to argue that it is at all realistic,” Crawford says. But that’s because in that scenario we’re restricting ourselves to achieving the goal of a crewed interstellar mission in a single human lifetime. We could, instead, invoke a plan that is dear to science fiction writers: the generation ship. Instead of going fast we could go slow, meaning that much less energy is required to accelerate the craft. The consequence is that the mission would take far longer than a single human life span. “You’d have some large, selfcontaining colony in which generations [of humans] live out their lives and it is their descendants who reach the destination,” Crawford says.
Travelling near the speed of light How long does it take light to travel through the universe? NAME OF TARGET Time it takes to get to target from Earth
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THE MOON
MARS
SATURN
1.28 seconds
12.5 minutes
1.1 hours
Interstellar travel
THE SPACESUIT
THE SPACECRAFT Visor
A key part of any space traveller’s equipment
While most of the journey would be far from any bright light, a visor is nonetheless important for when you are up close to a star. Without one, the searing light could easily blind you.
Oxygen supply While the environment inside your craft would have its own oxygen, if you needed to venture outside of your spaceship then breathable air is a must.
Scientists and science fiction writers have long dreamed up ways of travelling between the stars Daedalus In the 1970s, the British Interplanetary Society conducted research into a rocket that could travel between the stars. Their aim was to send their fusion-powered, 54,000-tonne spaceship to reach Barnard’s Star (which is 5.9 light years away) in 50 years.
Project Orion An idea from the 1950s and 1960s would have used controlled nuclear explosions to propel an interstellar craft. The difficulty was that many countries were (and still are) signed up to an international treaty banning the detonation of nuclear devices in space.
Breakthrough Starshot Communications
Water supply
When you’re encased in a spacesuit, having radio communication with your fellow astronauts is key – especially as you’re too far from Earth for quick help.
Water is a key ingredient for life. You’ll certainly need it if you’re roving out and about once you reach your destination.
The latest idea from Stephen Hawking and Yuri Milner is to send a swarm of tiny probes to the Alpha Centauri system by firing a powerful laser at sails strapped to the miniature machines.
Sänger Photon Rocket Eugene Sänger suggested using antimatter as the propulsion mechanism for a spacecraft in the 1950s, as when antimatter collides with matter it creates energy that could propel the craft forwards.
Bussard Ramjet One of the big problems with interstellar travel is the need to carry vast amounts of fuel. To get around this problem, a ramjet could theoretically use magnetic fields to scoop up interstellar material as it goes, which could then be used as fuel.
HOW INTERSTELLAR TRAVEL AFFECTS THE BODY Changes in gravity can affect bone mass Radiation from cosmic rays can cause radiation sickness Radiation can also cause cataracts Long-term isolation can cause psychological trauma
PLUTO
PROMIXA CENTAURI
CENTRE OF THE MILKY WAY
EDGE OF OBSERVABLE UNIVERSE
4.6 hours
4.2 years
30,000 years
46.5 billion years
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Future Tech
Interstellar road map Given how difficult it is to travel far from the Earth, where might our interstellar travels take us? tellar Inters ed spe erstellar
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THE LOCATIONS Alpha Centauri Distance from Earth: 4.37 light years Current travel time: 30,000 years Interstellar speed travel time: 43 years This three-star system includes Proxima Centauri, which is the nearest star to Earth after the Sun. It is believed there may be planets around these stars.
Barnard’s Star Distance from Earth: 5.96 light years Current travel time: 42,500 years Interstellar speed travel time: 60 years One of the fastest moving stars in the galaxy, this is also the closest star to Earth (after the Sun) that is visible from the Northern Hemisphere.
Wolf 359 Distance from Earth: 7.78 light years Current travel time: 55,500 years Interstellar speed travel time: 78 years This red dwarf is located in the constellation of Leo and it can only be seen through a large telescope.
Sirius Distance from Earth: 8.58 light years Current travel time: 61,250 years Interstellar speed travel time: 85 years Sirius is the brightest star in the night sky as it is one of the closest to us. It is part of a double star system.
Luyten 726-8 Distance from Earth: 8.73 light years Current travel time: 62,350 years Interstellar speed travel time: 87 years This star, seen in the constellation of Cetus, is actually a binary system of two stars encircling each other every 26.5 years or so.
Ross 154 Distance from Earth: 9.68 light years Current travel time: 69,100 years Interstellar speed travel time: 97 years This star, found in the constellation of Sagittarius, can only been seen with apertures of 3” or larger.
Ross 248 Distance from Earth: 10.32 light years Current travel time: 73,750 years Interstellar speed travel time: 103 years This small star in the constellation of Andromeda emits just 0.2 per cent of the Sun’s light.
Epsilon Eridani Distance from Earth: 10.52 light years Current travel time: 75,000 years Interstellar speed travel time: 105 years This bright star, visible with the naked eye, has a confirmed planet orbiting around it and has been a popular interstellar travel target in science fiction.
Lacaille 9352 Distance from Earth: 10.74 light years Current travel time: 76,700 years Interstellar speed travel time: 107 years Visible in the Southern Hemisphere with binoculars, this star is smaller and cooler than our Sun.
Ross 128 Distance from Earth: 10.92 light years Current travel time: 78,000 years Interstellar speed travel time: 109 years Ross 128 is a red dwarf star whose orbit around the Milky Way will bring it closer to us in the future.
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Interstellar travel
We already fire laser beams at the Moon, but for star sailing they would have to be a lot more powerful
Aubrey de Grey believes the first person to live to 1,000 is alive today, a boost to the idea of interstellar travel if true
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Satellites are already being significantly miniaturised. This CubeSat is just 10cm (3.9in) long on each side
Travellers to other solar systems may find a planet similar to ours but with different shaped landmasses
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© Shutterstock; Rex Features; NASA; JPL-Caltech; ESA; CXC; STSc; MPIA; V. Joergens; R.Thompson(Univ. Arizona); Tom Zagwodzki; Goddard Space Flight Center
However, in order to maintain sufficient genetic diversity on board – to prevent too much inbreeding – studies have suggested you’d need an initial crew of between 75 and 150 people. Providing living quarters and supplies for the equivalent of a small hamlet for hundreds of years would require your ship to be enormous – kilometres long in Crawford’s estimation. “You face engineering challenges either way,” he says. Either you have to build a small ship but struggle to get it up to the lofty speeds required for quick passage, or you have to struggle to build an enormous ship here in the Solar System that will carry hundreds of people for hundreds of years. The latter case is also particularly prone to ethical concerns. You’d be creating generations of humans ‘imprisoned’ on a craft with no memory of home and no hope of seeing the eventual destination. Of course, this is all based on the assumption that a human lifespan is somewhere close to 100 years. What if that figure is only a product of the times we live in? After all, we’re living twice as long on average than we did many centuries ago. Perhaps there is no upper limit to how long we can live. That’s certainly the view of gerontologist Aubrey de Grey, who sees ageing as a disease that’s curable like any other. He believes that the first person to live to 1,000 is alive today. A remarkable claim, but less so when you realise that he isn’t talking about one miraculous boost in medical understanding to extend your life that far. Instead, one initial breakthrough could extend your life sufficiently so that you’re always ahead of the medical curve, living ten years longer until another breakthrough occurs that will extend your life further. Then again, maybe he is wrong. Given all these significant hurdles, it’s no surprise that global space agencies, including the European Space Agency (ESA), are seriously looking into another alternative: human hibernation. ESA’s Topical Team on the subject is tasked with determining “a probability based on current knowledge of controlled use of human hibernation being applicable to human spaceflight in a foreseeable future, and rough estimates on the timeline, potential showstoppers, and gains.” If we could master such methods, the advantages are clear. You’d need a much smaller crew, and reproduction on board would no longer be necessary. It’s also better psychologically for those on board as they don’t have to experience the rigours of the voyage. Plus, as they are inactive, they won’t use as many resources, meaning the mass of the mission could be kept to a minimum. “It is very early days and no one knows if it is possible or not,” says Crawford, “but it’s not impossible to imagine that in 100 years’ time, human hibernation may be possible, making it easier to send humans to the stars.” If we do make it to the stars, it would make astronaut (which means ‘star-sailor’) a more accurate term for our space travellers. The challenges are great but, like all successful endeavours in human history, you can’t achieve something unless you set yourself a goal. It is almost certain that robots will go before us, as they did in the early days of space exploration. But, one day, it might just be possible that your descendants will gaze upon the continents, clouds and oceans of a familiar yet far-off world and be the first to set up a human outpost among the stars.
Future Tech
Space elevator
Launching into space is a hazardous process. Wouldn’t it be simpler if we could take a lift?
Riding the elevator The tether provides a physical link for the climbers to journey into space. Most likely the tether will be a ribbon shape and the climbers will simply clamp on and drive up it with rollers. Power could be provided through a carbon tether from solar panels on the counterweight, or carry solar panels lit by ground based lasers. The climbers would travel at about 200km/h (124mph), taking 7.5 days to reach GEO, making for a very different launch experience.
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A space elevator is the idea of building a lift connecting the ground to Earth orbit. The first person to consider it was Konstantin Tsiolkovsky (who was the first to set out the equations that govern orbital rocket launches), in 1895 he was inspired by the new Eiffel Tower to point out that if such a tower could be built 35,800 kilometres (22,245 miles) tall, you could go to space just by taking the lift up the tower. To appreciate why (and why 35,800 kilometres or 22,245 miles) we must consider how orbits work. When spacecraft launch into space they don’t just pass out of the atmosphere and start floating. Getting past the atmosphere is fairly easy; the boundary of space is only 100 kilometres (62 miles) up. To be in orbit, a craft has to be travelling fast enough horizontally (eight kilometres/five miles per second) that the tendency to be flung away from Earth is
Space elevator
“There would be no violent launch, just electric motors gently lifting you into space”
Russian scientist, Yuri Artsutanov, suggested that it might be possible to build such a structure if it was a cable in tension, rather than a tower in compression. In this case, a satellite is deployed in GEO and begins to wind a tether downwards, while another tether winds outwards with a counterweight on the end. Ultimately, the first tether touches down on Earth where it can be anchored while the counterweight, being flung outwards by the rotation of the system, balances the weight of the tether, plus some spare capacity for the weight of the elevator cars (climbers) moving on it. The concept was considered science fiction for many years, though, as no materials came close to the strength needed. That changed in the 1990s with the discovery of carbon nanotubes; cylindrical molecules of carbon that would be strong enough, if we can make them long
enough. A NASA study from 2000 proposed that a small 20-ton nanotube tether could be launched and installed from GEO. It would be anchored to a floating platform and then small robotic climbers would run up adding more material. This would build a one-metre (3.3-foot) wide tether, thinner than a sheet of paper but still extremely capable of lifting 20-ton climbers. Unfortunately, no one has made nanotubes longer than 50 centimetres (19.7 inches). But, a number of organisations are working towards Space Elevators. LiftPort Group in the US are developing a commercial carbon nanotube business in support of their plans, and intend to build a space elevator headed for the Moon with existing materials by 2020. So, we may even see a railway to the sky before the second half of this century.
Counterweight Escape velocity In some designs, the tether extends well beyond GEO. In one case three-times further. Payloads at the end would be flung away from Earth completely.
The elevator must have a counterweight above GEO to balance the weight below and keep it in tension, this could be a small asteroid, or even more tether.
Centre of mass The centre of mass of the whole system must be above GEO orbit so that the tether is always stretched out in tension.
GEO orbit Geostationary orbit is 35,800km (22,245mi) high. In this orbit it takes 24 hours to go around the Earth, so spacecraft match the spin of our planet, appearing to hover over the same place.
Climber The carriages, or climbers, would be electrically powered, either via the tether itself, or photovoltaic panels lit by ground based lasers.
Equator The space elevator would be attached at the Earth’s equator, so that the tether would stay aligned above its base.
Tether The tether will be made from carbon nanotubes, and most likely a one-metre (3.3-foot) wide ribbon to better accept small space debris impacts.
Low-Earth orbit station A space elevator could provide cheap access to low-Earth orbit. By some estimates it would only cost $100 per kilogram to ferry cargo by tether, compared to launches which cost upward of $16,000 per kilogram.
© Adrian Mann
balanced by the gravity trying to pull it back down, so that it continuously circles Earth. The higher the orbit, the faster the spacecraft must travel, and the longer it takes to orbit; 35,800 kilometres (22,245 miles) high is an orbit called "geostationary” (GEO). In GEO it takes 24 hours to make one orbit, so spacecraft appear to hover over the same spot on Earth - this is used for satellite TV so you get continuous signal. Travelling on a space elevator, you would slowly gain both the height and speed required to be in GEO at the top. There would be no violent launch, or highly stressed rocket engines, just electric motors gently lifting you into space over the course of a few days (it is the same as taking a train 90 per cent of the distance around the world). But we can’t build a tower that tall; no material comes close to supporting its own weight at such a height, but in 1959 another
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