Fifty years ago a young astronomer, indulging in a bit of interstellar voyeurism, turned a telescope on the neighbors to see what he could see. In April 1960 at the National Radio Astronomy Observatory in Green Bank, W.Va., Frank Drake, then 29, trained a 26-meter-wide radio telescope on two nearby stars to seek out transmissions from civilizations possibly in residence there. The search came up empty, but Drake’s Project Ozma began in earnest the ongoing search for extraterrestrial intelligence, or SETI.
Drake, who turned 80 in May, is still at it, directing the Carl Sagan Center for the Study of Life in the Universe at the nonprofit SETI Institute in Mountain View, Calif. Instead of just borrowing time from other astronomical instruments, those in the field now have purpose-built tools at their disposal, such as the fledgling Allen Telescope Array (ATA) in Hat Creek, Calif. But funding is scarce—the ATA growth stalled at 42 dishes of a planned 350—and astronomers have not yet gathered enough data to make firm pronouncements about intelligent life in the universe.
“Although we have ‘been doing it’ for 50 years, we have not been on a telescope very much of that time,” says Jill Tarter, director of the Center for SETI Research at the SETI Institute. “What we can say is that every star system in the galaxy isn’t populated by a technology that’s broadcasting radio signals at this time.”
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Theoretical astrophysicist Alan P. Boss of the Carnegie Institution for Science agrees. “The lack of a SETI signal to date simply means that civilizations that feel like broadcasting to us are not so common that the limited SETI searches would have found one,” Boss says. “There is still a lot of the galaxy that has not yet been searched.” One of the most extensive campaigns to date, Project Phoenix, surveyed nearby stars across a wide range of frequencies using some of the world’s largest radio telescopes. In nine years Phoenix sampled roughly 800 stars, less than one millionth of 1 percent of the Milky Way.
Even for stars that have been scanned, the parameters for a possible signal are frustratingly numerous. Like those for terrestrial radio, they include frequency (what station does it broadcast on?), time (24/7 or midnight sign-off?), type of modulation (AM or FM?), and so on. “At the very least this search is nine-dimensional,” Tarter says, “and we could guess right about what to look for and build the right instrument for eight of those dimensions, but we could still miss it because we got one wrong.”
Arguments for SETI and for widespread life in general have been bolstered by the confirmation that planetary systems are common around other stars. Most of the 400-plus exoplanets are scalding giants inhospitable to life as we know it. But in the next few years NASA’s Kepler space telescope, now surveying more than 100,000 stars for planets, should settle the question of how common Earth-like planets are.
Even on Earth-like worlds, however, technological, radio-broadcasting life may not be common. Many researchers hold out more hope for finding simpler life-forms, such as microbes or slime molds. Boss says that life of this kind should be widespread, but we will not have the technology to detect it for two decades at best.
But what if someone does pick up a signal from an intelligent civilization? The SETI community has protocols in place, such as alerting observatories around the world for verification, but the same cannot be said of the world’s governments. A United Nations–level framework does not yet exist to guide the contentious next steps—if we hear a shout from a potentially hostile neighbor, do we dare shout back?
It would not be an entirely new experience for Drake, who as a graduate student thought he had made a detection. “You feel a very special emotion if you think that has happened, because you realize everything is going to change,” he says, noting that we would soon be enriched with new knowledge of other worlds, species and cultures. “It’s an emotion you have to feel to understand, and I felt it.”