Sunday Times, 08 April 2012
There was a party in Arecibo, Puerto Rico, in January. It was, admittedly, a bit of a geeky do by the standards of Puerto Rican hospitality. “It was not exactly that kind of ‘party’,” Abel Mendez tells me.
There was live music, but no dancing, and excellent food at a restaurant on the beach. Abel, my Puerto Rican pal, says: “It was a good time. Cheers.”
The gig was a bit specialised for your average party animal. It was, in fact, the climax of a four-day conference to mark the 20th anniversary of the discovery of some oddities in the “millisecond pulsar PSR1257+12”, a coldly christened, rapidly spinning star 2,000 light years from Earth. These oddities were the biggest thing to happen in the lives of those non-dancing partygoers and, in truth, they may turn out to be the biggest thing in all our lives. You see, it was on January 9, 1992, that it really began to look as though we are not alone. What happened on that date was that a letter appeared in the science journal Nature, containing the momentous words “the pulsar is orbited by two or more planet-sized bodies”.
Thanks to some spectacular astronomy conducted at Arecibo’s giant radio telescope, we had, for the first time, detected planets outside our own solar system. The writers of the Nature letter spoke of the “tantalising possibility” that there could be more planets out there. They weren’t wrong. Current estimates suggest there are 160 billion planets in our galaxy, the Milky Way, and we have even detected a planet in Andromeda, our closest spiral galactic neighbour. Meanwhile, an international team led by the French studying red dwarf — small, cool — stars has estimated there may be 100 Earth-like planets no more than 30 light years from ours and, therefore, billions of potentially life-bearing planets in the Milky Way. But, of course, the really tantalising possibility is that lots of planets may mean lots of life, maybe intelligent life, and that really does set astronomical hearts pounding. In fact, many now believe that it’s not a matter of if we are to meet ET, but when.
You see, it was on January 9, 1992, that it really began to look as though we are not alone
“Since my childhood,” says Geoff Marcy, professor of astronomy at the University of California at Berkeley, “my big question has evolved from ‘is there intelligent life in the universe?’ to ‘how common is it?’…We’re trying to ascertain whether there is a galactic country club of civilisations that interact, and have combined their knowledge to arrive at a higher level of understanding of what life is about. I would love to know the answer before I die.”
Marcy and many other astronomers can talk like this because, since 1992, they have collected 760 confirmed “exoplanets”, the name given to planets outside our solar system. We also know of another 2,300 “candidates”, most of which almost certainly are planets, but will not be confirmed until the scientists are 100% sure. The closest known exoplanet to Earth is Epsilon Eridani b, which is only 10 light years away — but don’t get too excited, because one light year is 5.88 trillion miles and, without a Star Trekian faster-than-light warp drive, no human will ever get as far as Epsilon Eridani.
Nor will they ever get to the furthest exoplanets so far discovered in our galaxy: Sweeps-04 and Sweeps-11, both 30,000 light years away, one third of the way across the Milky Way. You are allowed, however, to get excited about four confirmed exoplanets, which have been classified as “potential habitable worlds”. The closest of these is Gliese 581d, which is 20 light years way. “Habitable” means they’re all a bit like Earth and could, therefore, be suitable for life. Terrestrial (Earth-like) planet finding (TPF) is now the hottest game in town; the Holy Grail of the exoplanetary explorers.
In fact, Gliese 581d, though almost six times as big as the Earth, has turned out to be more promisingly like it than expected. In May last year, a French simulation of the planet’s climate found that it was stable and could sustain liquid water on the surface. This made it the first planet to be found in the “habitable zone”. “Searching for Earth-like planets,” Marcy says, “around nearby stars and assessing their habitability is one of the great scientific questions in human history. It reminds me of seeking the origins of human genetics, of the transoceanic voyages of the 1400s and 1500s.”
Finally, and again excitingly, within our own solar system many now think not only Mars but also the Jupiter moons Europa and Ganymede and the Saturn moons Titan and Enceladus could contain microbial life. Enceladus is the favourite; it is certainly the most beautiful. Great plumes of cold, pure water ice leap into space from its frozen surface. On Earth, where there is water, there is life.
The idea of exoplanets has been around for a long time. The Greek philosopher Epicurus speculated about alien worlds and, in the 16th century, an Italian monk named Giordano Bruno suggested the Earth was just one inhabited planet among many. He was burnt at the stake for this heresy. The point was that, for the Catholic Church, the Earth must be the centre of the universe. Copernicus and Galileo proved this wrong and, ever after, we have had to adjust to the fact that Earth is merely a tiny speck in a cosmos full of tiny specks.
So, to the modern scientific imagination, exoplanets seemed inevitable, but, for almost four centuries after Galileo, none could be seen. Perhaps the Earth was special after all; exoplanets were rare, or even nonexistent, and we were just the one freakish case of life in the cosmos. But now, in only 20 years, the scientific consensus has moved from a bleak, empty universe to one that may be teeming with life.
Don Pollacco is an exoplanetary star. Outspoken, funny and very smart, he is a professor of astrophysics at Queen’s University, Belfast. He is also one of the brains behind SuperWasp, which, believe it or not, holds the world record for exoplanet discovery. SuperWasp telescopes are conceived and built in Britain, but have to be located in clearer, higher sites abroad. Their relative cheapness and the way they are put together out of available parts, such as Canon lenses, puts them in the British-boffin tradition of independent technological innovation, usually conducted in the garden shed.
“We’ve got 80 of them now,” he says proudly, “all confirmed.” Pollacco, a gleefully subversive character, doesn’t believe in most claims for confirmed planets and reckons there are only 170, not 760, which means he has found almost half. The reason is, most were found by spectroscopy — the measurement of radiation — as opposed to his preferred “transit method” (see below) and Pollacco thinks transit is much more reliable.
Their relative cheapness and the way they are put together out of available parts, such as Canon lenses, puts them in the British-boffin tradition of independent technological innovation, usually conducted in the garden shed
The current runner-up in the race to find more planets is the Hungarian Automated Telescope Network, which, inexplicably, is not Hungarian but American. Anyway, there are two Wasps — which stands for “wide angle search for planets”: one in South Africa and one in the Canaries. Basically, they’re just big versions of your digital camera and cost £500,000 each. They consist of eight paparazzi lenses (Canon 200mm f1.8s) and a super-pure silicon sensor and, er, that’s it. Unfortunately, the Americans are catching up, thanks to a similarly basic system that has the advantage of being in orbit. But first, some science.
Finding a planet next to a star is fiendishly difficult. Stars are big and bright; planets tend to be smaller and darker. Stars, other than our own sun, are also a long way away. The closest is Proxima Centauri, and that is 4.2 light years (around 25 trillion miles) away. Ever more refined technologies have been devised to conquer these problems, but, so far, the simplest is still the best.
What Pollacco’s Wasps do is photograph the stars as clearly as possible so that any variations of luminosity can be detected. Regular, though tiny, dips in the light coming from the star indicates a planet is passing across the disc of light. This is known as the transit method and, when combined with the radial velocity or Doppler method, it can yield a startling amount of information about the planet, including size, mass and the orbital distance from the star.
There are, potentially, more exotic ways of getting better information. These range from infrared spectroscopy, through vector vortex coronagraphy, to the super-weird gravitational microlensing that uses Einstein’s discovery that light bends round stars in ways that neither I nor, I suspect, you will understand. Gravitational microlensing is good at finding very distant planets — it was used to find that planet in Andromeda. Unfortunately you can’t use this method to confirm a finding because the conditions under which it works only happen once. On the other hand, microlensing does produce many candidates.
If 1992 was the first slow start of all this, 1995 was the year exoplanetary exploration really took off. A planet was confirmed orbiting a “main sequence” star — a normal one like our sun, rather than a pulsar — and it became clear that exoplanets were going to be the next big thing in astronomy, if not human history. Scientists then went into a huddle to discuss the best way of putting something in orbit to detect more planets. All the different technologies were discussed. All would be expensive — done properly the project could cost $10 billion — so ESA (the European Space Agency) and Nasa made a deal to do it together. Then it all went horribly wrong.
Incandescent with rage, Marcy says it was “a diplomatic failure, a technical failure and a scientific failure”. He primarily blames Nasa and gives angry lectures about the agency’s indecision and profligate ineptitude. Cowed Nasa attendees can only agree. Basically Nasa kept changing its mind about the right technology, effectively broke the ESA deal, and the whole thing descended into funding squabbles and technical uncertainties.
“We lost one decade,” says Marcy, “now we’re going to lose two. There is no chance of a new mission before 2020.”
Except that, in the meantime, we have Nasa’s surprise package, Kepler. Stung by accusations that, in effect, it was an organisation whose primary goal was to find the most expensive ways of getting into space, and by the threat of cheaper private-sector competition, Nasa had started a programme of “quick and dirty” — ie, cheap — missions. So, instead of pursuing the multibillion-dollar exoplanetary exotica, it came up with a $300m plan to put a big digital camera in space. The Kepler telescope — named after Johannes Kepler, probably the greatest of all astronomers — was launched in 2009. Of course, this being Nasa, it actually cost $600m and another $30m a year to run. But the big thing, the huge thing, about Kepler is that it works far better then even the most rabid exoplanet hunter could have imagined.
“Kepler came in under the radar,” says Marcy, “and obviously it has been a spectacular success. It is utterly simple, a wide-angle camera with a 95-megapixel detector, it is literally no different from a home digital camera.”
“I suspect Kepler will get close to tens of thousands of planets,” says Duncan Forgan, an astrophysicist at the University of Edinburgh. “We’re going through a seismic change in the field.”
Kepler has yet to pass Pollacco’s number of confirmed exoplanets, but it soon will because of its 2,300 candidates, almost all of which are expected to be confirmed. The main problem is the fact that stars have starspots, just as the sun has sunspots, and these dim the light in the same way as a passing planet. But, once this possibility is eliminated, astronomers can usually be sure they have found a planet.
So now the cosmologists have a vast and growing catalogue of exoplanets to browse. Obviously the most interesting are those that might contain life. My Puerto Rican friend Abel Mendez, a professor of astrophysics, maintains the Habitable Exoplanets Catalog online, which currently lists four habitable planets and 30 potentially habitable exomoons.
Unfortunately it is not clear how far we can take this without spending billions. Scientists are lobbying Nasa to extend the working life of Kepler. It was intended to be operational for three and a half years, but it could be extended by another two years. This will produce thousands more planets, but Kepler is not the right machine to detect life. For that, some very expensive kit has to be placed in orbit.
What would we find? Some years ago the great environmentalist James Lovelock, while working for Nasa, worked out that the best way to look for life on other planets was to test the atmosphere. Life, he pointed out, does not just passively adapt to environments, it changes them. So life constantly modifies the Earth’s atmosphere. We don’t have to fly to distant planets to see if they harbour life, we can just observe their atmospheres.
Such observations might reveal microbial life. Over the past 40 years we have discovered microbes known as extremophiles in ever more difficult conditions on Earth — deep beneath the ocean floor, in the cores of nuclear power stations and so on — and this suggests such bugs could survive in a much wider range of planetary environments. But, in the off-the-record words of one exoplanet hunter: “Would you be happy with that? Would anybody? Who’s going to get excited about a few bugs?”
Much more exciting would be intelligent life or, failing that, plants and animals. But these are several thousand times more unlikely than microbes. “There are,” says Duncan Forgan, “good reasons to be sceptical about finding large-scale, complex life as we do on Earth. Extremophiles are very hardy bacteria, but they are not more than one cell or a handful of cells. So going to a planet and finding alien cows in a field of grass is much less likely than finding alien rocks with layers of scum clinging on to them for dear life.”
The further problem is that alien life may not just be lost in the vastness of space, it may also be lost in time
Forgan explains that the big thing we would be looking for if we ever put up Kepler’s successors will be a phenomenon with the glorious science-fiction name of red edge. Plants eat light and cause changes in the way light is reflected from the Earth. It is “red-shifted”. If we found another planet with the same red shift then we could be pretty sure it contained plant life.
There is, however, a gaping logical hole in the centre of this entire project. This is technically known as the “drunk-under-the-lamppost-problem”. A drunk has lost his keys and is searching for them in the pool of light beneath a lamppost. “Why are you looking there?” asks a passer-by. “Only place I could see them,” replies the drunk.
We only have one example of a life-bearing planet, Earth, so, like the drunk, when we look for life elsewhere, we look in the only places where we think we can find it.
Yet it is entirely possible that other forms of life could be utterly different; it could be something as weird as “a super-intelligent shade of the colour blue”, an invention of the author Douglas Adams. Even on Earth we’ve discovered bugs that eat iron and excrete rust, so we already know that life can be very weird indeed. Some think we should take Adams’s imagined exotica to heart. At the University of St Andrews, Martin Dominik, who seeks exoplanets using gravitational microlensing, is so much in favour of looking for super-strange life forms, he’s not particularly interested in finding another Earth. “We’ve already got one,” he says. “I don’t want to just find another.”
The further problem is that alien life may not just be lost in the vastness of space, it may also be lost in time. We have only been technologically advanced enough to communicate to the universe for about 150 years, since the harnessing of electricity and radio waves. We know perfectly well we are capable of destroying ourselves or being destroyed by, for example, a collision with an asteroid. “Maybe there’s a 0.1% chance we will be wiped out every year,” says Geoff Marcy. “That means we might only last 1,000 years.”
Other communicating civilisations may have come and gone for the same reasons. The universe may have been intelligently alive in the past and it may be in the future, but it may not, apart from us, be alive now.
“The Earth is four billion years old,” says Don Pollacco. “The universe is 13 billion years old. The human race has been around for 1m years and we’ve been technically capable for 150 years. What’s the likelihood ofmeeting a race similar to ours? They might be millions of years more advanced or less advanced. Would we recognise them? Would they want to talk to us? Maybe they’ve already been here and just regarded us like cave men.”
Though the odds may be against them, the enthusiasm of the exoplanetary explorers burns more brightly than ever, however. They scan Kepler’s regular downloads of thousands of candidates hoping for the Holy Grail — an Earth-sized planet orbiting just far enough from a medium-sized star so that its surface temperature hovers between 0 and 100C, allowing water to remain liquid. Add to that a life-altered atmosphere with a red edge and, well, that would be some party and, I bet, this time there would be dancing.