This month marks the 50th anniversary of a day some say changed the course of science. In April 1960, Frank Drake, an astronomer at the National Radio Astronomy Observatory in West Virginia, turned a radio telescope (basically a huge antenna) toward two nearby stars. Drake thought he might—just might—hear signals broadcast from another planet. “For the first time in history, we had the chance of detecting a civilization no more advanced than our own,” he says today. “For all we knew, every star in the sky had a civilization that was transmitting.”
Of course, Drake didn’t hear any alien broadcasts. But his experiment (dubbed Project Ozma for the princess of the land of Oz) marked the beginnings of what’s called SETI: the search for extraterrestrial intelligence. He’s spent half a century trying to answer one of our most enduring questions: are we alone? Today, an answer seems tantalizingly close. Scientists have now found hundreds of previously unknown planets, and even water in our own solar system; the new Allen Telescope Array, with 350 interlinked radio dishes, promises to vastly improve the search. (It’s run by the University of California, Berkeley and the SETI Institute, where Drake now works.) If the universe really is teeming with life, though, why haven’t we found it yet?
Physicist Paul Davies, who directs Arizona State University’s Beyond Center for Fundamental Concepts in Science, addresses this in his new book, The Eerie Silence: Renewing Our Search for Alien Intelligence. “We need to think more creatively, and give up hope that some benevolent alien community will send us a ‘Hi guys’ message,” says Davies. After all, it takes time for radio signals to travel through space; if we found a civilization 1,000 light years away, it’d take at least 2,000 years for us to send them a message, and get a response back. (“However powerful their instruments, they can’t go faster than light,” Davies says.) Luckily, we don’t need to pick up a message to know for sure we’re not alone. “We merely have to see a footprint,” he says. And scientists are chasing that footprint not only in distant galaxies, but in our own solar system—and here on earth.
When Project Ozma began, astronomers didn’t know if there were any planets outside our solar system. Since then, about 400 have been found in our neck of the galaxy, and efforts to find more are accelerating. Last year, NASA launched the Kepler satellite, a powerful planet-finding telescope that continuously monitors 100,000 stars, looking for the telltale dip in brightness that occurs when a planet passes over them. (The first earth-like planet pinpointed outside our solar system is thought to be scorching hot and volcanic.) Set to launch in 2014, the James Webb Space Telescope will be able to study distant planets’ atmospheres, looking for gases like oxygen and water vapour.
Perhaps most surprisingly, water has been found on bodies in our solar system—including the earth’s moon. Once thought to be bone-dry, experts now say there could be millions of tons of ice buried there, which might help establish lunar colonies one day. For SETI enthusiasts, an even more exciting prospect lies further afield. One of Jupiter’s moons, Europa, is wrapped in an icy shell that’s believed to cover an ocean, one that could be many times deeper than our own. Tidal forces created by the pull of Jupiter and its satellites might even warm the water. “The big question is whether evolution has been able to proceed,” Drake says, adding that some of our own Arctic jellyfish “might be perfectly happy” in the ocean on Europa, which has a very thin atmosphere. NASA’s looking at sending an orbiter to Europa in 2020, arriving by 2026, to learn more about whether it might be able to harbour life.
These latest discoveries have got even senior scientists taking a serious look at the possibility of extraterrestrial life. In the U.K., where the national science academy recently hosted its first-ever conference on the subject, the Queen’s own royal astronomer suggested aliens could be “staring us in the face and we just don’t recognize them,” because we’re looking for something “very much like us.” Davies agrees. It’s taken four billion years for humankind to get to where it is today, but an alien civilization could be far older: planets in other galaxies “could have had intelligent life on them five billion years ago,” he says. “The mind boggles.” Such an advanced race certainly wouldn’t resemble bug-eyed Martians of pop culture. They’re more likely to be “post-biological,” Davies believes—part organic, part manufactured, and designed by earlier versions of themselves. It’s a bleak vision of the future, but one he believes is inevitable. “I’m a great fan of human beings, but to say we’re the pinnacle of intelligence would be foolhardy,” he says.
While conventional SETI has been focused on outer space, Davies thinks we should look closer to home: in this solar system, on our planet, even in our own genes. “Suppose we found evidence that, 100 million years ago, an expedition passed through our solar system and did some engineering,” he says. What if aliens sent a probe—might it still be here? Or maybe they engineered viruses, “the space-age equivalent of a message in a bottle,” and sent them across the galaxy, he suggests. Genome sequencing is now a major industry, he writes, so why not search our genomes for suspicious patterns? And why not look at geological records, too? If we found an ancient plutonium deposit, Davies believes “it would constitute strong evidence for alien nuclear technology,” although to his knowledge, nobody’s yet looked for one. Such a clue “might not say who, or why, or if there’s anyone still there,” Davies says. “But we could say, we’re not the only intelligent life.”
Even so, the search for extraterrestrial life is stymied by one big question—we still don’t know how life appeared on earth, let alone in outer space. “We have a good theory of how life evolves,” Davies says. “But we have no idea how life began. It could be a very likely event, or a freak accident.” (Gary Ruvkun, a genetics professor at Harvard Medical School, has suggested DNA might have originated on Mars or further afield, landing here on a meteorite. Ruvkun’s working on a NASA-funded project called the Search for Extraterrestrial Genomes, which intends to search soil and ice samples on Mars for DNA and, if it’s found, compare it to our own.) Beyond that, we don’t know whether intelligence is likely to develop, or if it’s a rare occurrence. If it’s common, Drake writes, “Why didn’t dinosaurs evolve big brains, build rockets and fly to the moon?”
Luckily, scientists have the ideal laboratory to study the genesis of life—earth. Here, all sorts of bizarre creatures could potentially teach us about adaptation on other planets; last year, for example, researchers found microbes buried under an Antarctic glacier, where the lack of light, heat and oxygen would have led many to believe nothing could survive. (These microbes seem to breathe iron leached from bedrock.) NASA recently reported finding pink, shrimp-like creatures on the underside of an Antarctic ice shelf 180 m thick. And Felisa Wolfe-Simon, a colleague of Davies, is searching for microbes that incorporate arsenic into their innards.
Finding “weird life” here on earth, Davies believes, could be crucial in identifying something even more exotic—what he calls earth’s “shadow biosphere,” which he thinks is the key to whether we’ll ever find alien life. Scientists have assumed that all life here sprang from one common genesis point, Davies notes; but what if there were two? What if we found a creature so strange that we could not possibly be related to it, no matter how far back along the tree of life we went? This, he believes, is the critical question. “If life started more than once on earth, we could be virtually certain that the universe is teeming with it,” he writes. “It is inconceivable that life would have begun twice on one earth-like planet but hardly ever on all the rest.”
Fifty years in, Davies remains optimistic about the search. He believes we could find a shadow biosphere within the coming years, which would be, he says, “the biggest discovery in the history of biology,” turning everything we once knew about life on earth on its head. As for whether we’ll ever find intelligent life, well—given the mind-boggling stuff we’re still learning about earth and beyond—it seems impossible to predict. “Never underestimate life,” Drake says.