Astronomers have been scanning the skies for more than 50 years now listening for radio broadcasts that might betray the telltale hum of an alien civilization out among the stars. They haven't found anything yet, but that hardly means much, since the Milky Way is vast, and the formal hunt for something smart out there known as SETI, or Search for Extraterrestrial Intelligence has been run on a shoestring. "If you dipped a drinking glass into the sea and came up with nothing but water," astronomer and alien hunter Jill Tarter is fond of saying, "you wouldn't conclude that there are no fish in the sea."
SETI got a boost a few years ago with the construction of the Allen Telescope Array (ATA), in Hat Creek, Calif., and despite some money troubles last year, the array's 42 radio dishes are back online. Now the big problem is combing through all the data pouring in through them to tease out promising signals. But Tarter, director of the Center for SETI Research at the SETI Institute, which runs the array, hopes that a new project will help. Called SETIlive and funded in part by Tarter's 2009 TED Prize, it crowdsources some of the detective work to citizen-scientists armed with uniquely powerful pattern-recognition tools: the human eyes and brain.
"It's an experiment with a great big E," says Tarter. "We don't know how it will work out." But then, she says, that was true of a sister site called Planethunters.org, which lets dedicated amateurs look for evidence of planets around other stars in the data stream from the Kepler space mission.
In both cases, the amateurs are hoping to see signals that screening software programs haven't picked up. With planet hunting, the signature of a possible new world is sometimes too subtle for a computer to see. With SETIlive, the computers don't even try. The Allen Array telescopes pick up a range of radio frequencies when they aim at a star, but, says Tarter, they don't process all of them because there's so much contamination from radio signals generated on Earth. "It's a shame," she says, "because you can imagine that in bands where Earth is radio-loud, extraterrestrials might think, 'Oh, that's a good band we can use to make contact.' "
The only way for SETI searchers to sift through those bands would be to use a lot of computing power, but that's inefficient to say nothing of expensive. The untapped energy of eager amateurs, however, is practically limitless, and anyone can sign up. The volunteers get a live feed of one of the messy data bands from the Allen Array and look for interesting anomalies. In particular, they're trying to see some sort of radio blip being picked up by one dish in the array but not others. Since each dish points at a different star, says Tarter, "If the signal is really coming from E.T., it should appear in just one." If it shows up in two or three dishes, it's probably a satellite or a trucker using his C.B. radio or something else equally prosaic.
If the signal does appear in just one channel, though, the volunteer flags it so ATA observers can conduct the next test: move the dish away from its target and ask the amateur observer to look again. If the signal is still there, it's not coming from the star in question. If it's not, the telescope tries moving back, then away again. "If this happens for five cycles," says Tarter, "then we" meaning the SETI Institute's top scientists "get an alert." That's still a long way from confirming an alien signal, since the Earth is a cacophony of radio interference, but it helps scientists focus on only the most promising candidates.
There's one more challenging element of the work, though. Because quick follow-up is essential to this process (you never know when E.T. is going to shut off his transmitter), amateur observers have just 90 seconds to scan each new screen grab as the telescope moves toward and away from the star. "Really," admits Tarter, "it's not an easy task." But citizen-scientists seem to love the work. SETIlive and Planethunters.org are part of a larger umbrella organization called https://www.zooniverse.org/, which started out as a project called Galaxy Zoo. The idea there was to let amateurs classify the types of galaxies in Hubble Telescope images a huge task, considering there are hundreds of thousands of galaxies out there.
Zooniverse has since expanded to projects that let amateurs classify craters on the moon, test climate models by poring over old weather data gathered by ships, identify different types of whale sounds and more. "It's an excellent way to do outreach and education," says Chris Lintott, who runs Zooniverse, "but it's also about letting everyone participate in real science." Starting this week, that will include participating in what might be the most thrilling search of all.