THE WEEKEND AUSTRALIAN MAGAZINE
In the new space race, respected scientists are rushing to join the search for life on other planets.
By Wilson da Silva
SUDDENLY, life out there is in. Astrobiology used to be called “searching for aliens” and no self-respecting scientist would be caught dead admitting any involvement. Now, astrobiology attracts high-profile scientists, respected journals are eager to publish their work and researchers from diverse disciplines are crowding its international conferences.
“It became more credible in the mid-1990s,” says Baruch Blumberg, outgoing director of NASA’s Astrobiology Institute. “Now the question is whether we live in a universe rich with life . or one in which we are completely alone. Lately, the evidence has been stacking up on the side of life.”
It’s not just the spate of new planets discovered that has boosted scientists’ spirits; there’s the startling discovery that life is more tenacious and adaptable than previously thought. Scientists have recently found living things in places once thought impossible: frozen Antarctic rocks; alongside poisonous volcanic vents on the seafloor; in super-pressurised cavities kilometres below ground; even embedded for millennia inside salt crystals. Add to that the recent discovery that water - the one essential ingredient for life as we know it - flows in oceans below the icy crust of Jupiter’s moon, Europa. Mars, too, has been found to have large reservoirs of water underground - raising the tantalising possibility that if life did emerge, it may still be there, eking out an existence deep below.
Following the jaw-dropping discovery in 1996 of what appeared to be tiny microbial fossils in Martian rocks that fell as meteors in Antarctica, then US President Bill Clinton charged NASA with the mission to seek extraterrestrial life. This led to the creation of NASA’s $US22 million Astrobiology Institute, a central office that coordinates multidisciplinary work around the world.
Today the Astrobiology Institute is a network of 15 research teams and 740 researchers in the US alone, and four affiliated centres overseas: in Britain, Spain, France and the new Australian Centre for Astrobiology at Macquarie University in Sydney, which opened last November.
Blumberg says the multidisciplinary approach is essential. “We need astronomers to find new planets and establish their habitability . chemists to understand the transition from carbon-based molecules to life itself, palaeontologists to find and understand the earliest forms of life, and climatologists, planetary scientists and researchers from nearly every field. And we need biologists too, to trace the evolution of life on Earth and define its limits.”
Blumberg’s career exemplifies this approach. A clinical researcher, he won the Nobel Prize for Medicine in 1976 for discovering the hepatitis B virus and developing a vaccine that has since saved millions of lives. He has been a commanding officer in the US Navy, worked as a doctor in a large New York hospital and studied infectious diseases in the isolated swamps of Suriname. Despite his practical medical background, Blumberg is an enthusiast for the esoteric new field.
“I consider it one of the most promising new fields of science, because it forces scientists to look at very basic questions from a totally new perspective,” he says. “That only increases the chances that people will make exciting new discoveries . maybe even fundamental ones.”
In 1985, two young astronomers, Geoff Marcy and Paul Butler, began looking for “extrasolar” planets. At the time, it wasn’t even known if any planets existed beyond our solar system. Most fellow astronomers thought the pair were throwing away perfectly good careers looking for them.
At the time, the duo reasoned that if there are alien civilisations out there, they live on planets. And since none of the nine planets that orbit our Sun show signs of intelligent life, aliens will likely live on planets orbiting other stars. But where were they? “Other scientists were embarrassed for me when I mentioned what we did,” Marcy recalls. “Most thought it was too close to science fiction.”
It’s a different story these days. About 100 extra-solar planets have been discovered in the past seven years. Butler, a staff scientist at the Carnegie Institution of Washington, and Marcy, professor of astronomy at the University of California at Berkeley, have found more of them than anyone else. In doing so, they have helped dispel one of the reasons to dismiss extraterrestrials.
“When we started thinking about the problem back in 1985, there were only nine planets we knew about, and they were orbiting our Sun,” says Marcy. “Now there are more than 100 beyond our solar system . astronomers are discovering them at the rate of one per month now. So if you ask me, how common are planets - it’s looking like they’re very common. The more we look, the more sensitive our instruments become, the more we find.”
But it’s one thing to have planets, quite another to find livable ones. None of those discovered so far are anything like the Earth. They are very large and inhospitable to life as we know it, with surfaces baked molten by suns that are too close, or so massive and dense that any creature would be crushed by its own weight.
So while Marcy and his ilk have found a swag of new real estate, none of it has been very appealing. This doesn’t mean that planets like Earth don’t exist; they probably do, but we just can’t see them. We occupy the sparse outer suburbs of the Milky Way galaxy, so far away from everything that even Alpha Centauri, the nearest other star, is 4.3 light-years away (the distance light would travel in 4.3 years).
Within the nearest 100 light-years of Earth there are only 1000 or so stars. And while our galaxy may be populated by 400 billion stars - and therefore, 400 billion suns, each potentially carrying its own brood of planets - the Milky Way is a whopping 40,000 light-years across. That’s a lot of distance to cover if you’re looking for tiny specks of dirt in a vast and empty field of darkness. As a result, even the best telescopes cannot see planets around another star. Planets are only visible because they reflect sunlight; at such enormous distances, the reflected light is too weak, overwhelmed by the fiery incandescence of its parent star.
Since they couldn’t directly see planets, Marcy and Butler developed an indirect technique: they looked for the effects a planet would wreak on its parent star - a kind of “wobble”. Even something as massive as our Sun - some 1.3 million times larger than the Earth - is slightly affected by the Earth’s annual rotation around it. As the nine planets in our solar system orbit the Sun, each adds a tiny wobble to the Sun’s own spin.
In 1988, Marcy and Butler began observing nearby Sun-like stars over long periods of time, hoping to come across a telltale wobble. They could then use this to estimate a planet’s mass and orbital period, and even establish whether the star was carrying a single planet or a clutch of them.
They soon bagged their first one, and other astronomers began to follow. Based on how frequently new planets are being found, astronomers now suspect that half of the 400 billion stars in our galaxy have planets. Of those, half again are likely to have more than one planet.
But finding life isn’t just about finding planets, according to Professor Malcolm Walter, director of the new Australian Centre for Astrobiology. A habitable planet has to be far enough from its parent sun so its oceans won’t boil away but not so far that they would freeze solid. It has to have volcanic activity to develop an atmosphere, and enough gravity to hold on to it, but not so much vulcanism that it creates a runaway greenhouse effect. It may need to have been bombarded by comets to give it oceans and a stew of carbon-based molecules from which life can emerge. And it may be essential to have a polar magnetic field, since this protects us on the Earth’s surface from the deadly cosmic rays that are constantly blasting the planet.
It makes life sound fairly improbable, Walter admits, but like most astrobiologists he is unfazed. “We’re talking about very large numbers here. There might only be one in a hundred planetary systems in the galaxy that are inhabitable. But that still adds up to lots of planets.”
After all, having a magnetic field is not unique to Earth, and volcanic activity has been observed elsewhere in our solar system. Where water can appear, it has; and atmospheres form wherever they are able, as they have on Venus, Earth and Mars. And scientists know that the carbon-based molecular building blocks of life are scattered like stellar fairy floss throughout the universe, in massive clouds that fill the spaces between the stars. “It’s just a matter of time before Earth-like planets in Earth-like orbits are discovered,” says Walter.
The question is, would we recognise aliens if we saw them? Increasingly, scientists cannot even agree on what life is. Take the Martian microfossils; sceptics insist that the fossils are too small to house the organs of the average bacterium; but then, Queensland scientists claim to have discovered a new class of super-tiny microbes that are as small as those in the Martian rocks.
Surely defining life should be easy - anything with genes that consumes energy and reproduces. But as Blumberg points out, viruses have genes, consume energy but can’t reproduce; they hijack living cells or bacteria and force them to make copies of themselves. Or take prions, the strange protein chains that cause mad cow disease - they don’t have any genetic material at all, yet they make copies of themselves and spread like bacteria. Little wonder scientists still argue about the results of the two Viking robot probes that landed on Mars in the mid-1970s; after conducting a battery of tests for bugs in soil, most were negative . but one was positive.
“If we find living things that don’t fit our preconceptions, then we have to be prepared to abandon our definitions [and] . establish new ones,” says Blumberg. “Part of the problem is that we only have one model for life, and that’s here on Earth. There may well be others that are just as valid.”
The really big unknown is intelligence, says astrophysicist Jill Cornell Tarter. Does it naturally arise as creatures grow in complexity, or it is a rarity in the universe? If intelligence is common, does every civilisation develop cities and high technology - or are they happy to discuss poetry while frolicking like dolphins at sea? If they have technology, would they wonder if there are others out there? And would they try to contact us?
Tarter believes they would. Intelligence, she argues, is a natural by-product of curiosity, and curiosity leads intelligent creatures to ask questions. No manner how you cut it, she says, an intelligent civilisation will eventually wonder if there are others out there . and will try to communicate with them. “For the first time in history, we can begin to try and find scientific evidence for life beyond the Earth, as opposed to having to rely on belief,” says Tarter. “If there are other civilisations out there, we now have the technology to detect them.”
Tarter is director of California’s SETI Institute, a $US10 million-a-year, privately funded research centre devoted to the search for extraterrestrial intelligence (hence its name). She was also the inspiration for Jodie Foster’s character in the 1997 Hollywood blockbuster Contact, based on a bestselling novel by astronomer Carl Sagan. Which is no surprise, really; she and Sagan were close friends, both fascinated by the idea that the universe might be teeming with alien civilisations. Both shared an impatience to find the answer. And both battled cancer, although only she survived – Sagan’s death six years ago was a deep loss to her.
But then, Tarter is used to going up against the odds. Ignoring the advice of her teachers, she took advanced science courses at high school, often the only girl in her class. She went on to the prestigious Cornell University in New York, and was the only woman among 300 engineering undergraduates. Distantly related to the university’s founder, she was unable to claim a scholarship bequeathed to his descendants: she had to be male. Tarter nevertheless became the first woman to land the Procter & Gamble scholarship, and went on to complete a doctorate in astrophysics at the University of California at Berkeley.
For years, Tarter and her colleagues at SETI have been targeting the nearest 1000 Sun-like stars, listening for a beacon from an alien civilisation. For a few weeks a year, they use some of the world’s most sensitive radio telescopes - including the Parkes dish in country NSW. Purpose-built ultra-fast computers scan millions of frequencies simultaneously, each for just five minutes. And they search in a section of the radio spectrum that is relatively quiet - the theory being that since most of space is littered with noise, aliens would use the quiet bandwidths to communicate.
No alien signals have yet been detected, although there have been a number of false alarms, usually caused by satellites or other interference. In a few years, a dedicated array of 350 smaller dishes in California - under construction thanks to a donation by Microsoft co-founder Paul Allen - will begin scanning the heavens 24 hours a day.
Tarter suggests that alien civilisations might have technology sensitive enough to pick up our television signals, which have been leaking from Earth for more than half a century, and would now be detectable 50 light-years away . they might therefore be returning the call. But more likely, she says, they will have set up a powerful beacon that transmits a signal in all directions - a kind of “village bell” to let emerging civilisations know that they are not alone.
“We don’t know what the probability of the evolution of intelligence is - we can’t set a number,” Tarter told The Weekend Australian Magazine. “And in that case, I think the right thing to do is to look. If we don’t detect a signal from any of the 1000 stars on our target list, we’ll make a list with 100,000 stars, and then one with a million. There are almost a half trillion stars in our Milky Way galaxy alone. So we’ll keep trying.”
It’s a gargantuan task. But there have been Earth-bound benefits, she argues: SETI technology, which searches rapidly through a confusing haystack of random data, has dramatically improved the detection of breast cancers, and the project has attracted a whole generation of starry-eyed students to science.
Tarter expects the search will take decades, maybe even generations, but will eventually be successful. And while optimistic about the likelihood of intelligent life, she dismisses UFOs and alien visits. Travelling to even the nearest other planet in a lifetime would take the amount of energy Brazil uses in a century, she says. Unless aliens have been able to twist the laws of physics in ways we can’t comprehend, we are unlikely to ever meet them face to face . if they have a face.
But Tarter would be happy to just talk over the radio, even if the conversation consisted of the only language we’re likely to share - mathematics - and even if we had to wait 50 years between transmission and reception. In fact, she muses, it would be momentous enough just to know we weren’t alone. But even if a signal were never detected, it doesn’t mean no-one’s out there; extraterrestrials may be shy, or cautious, or have moved on from radio, or are not broadcasting in our direction. “The lack of a signal does not prove extraterrestrial intelligence doesn’t exist . or even signals don’t exist,” she says. “It may be we just can’t detect them.”
But it might also mean that humans are alone in this vast universe, the only ones who gaze up and wonder. That, too, is valuable information, she says. “It means intelligent life is a rare and precious thing. We should take a bit more care of our planet, and of ourselves.”