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The array's first phase of 42 telescopes was completed this year. To build the full observatory, the SETI Institute will need a lot more money. (Seti Institute)

Can We Hear Them Now?

Speak up, space aliens. These 42 new radio telescopes are all ears.

IN The Cascade Mountains of northern California, within sight of Mt. Shasta’s snow-topped, 14,000-foot peak, lies the high valley of Hat Creek, where they say the fishing is good. People come here in the summer for a little R&R among the tall trees, away from modern technology and its discontents. Strange, then, that the valley should also be home to one of the most futuristic projects on the planet—the Allen Telescope Array, the first radio observatory built expressly for the Search for Extra-Terrestrial Intelligence. The late physicist Philip Morrison, one of the founding fathers of SETI, called the search “the archaeology of the future,” an attempt to learn whether civilizations more advanced than ours exist. Some might call that possibility unlikely. Then again, so may be the long-term survival of humanity. And we still hold hope in that.

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On this warm day in March, Jill Tarter is sitting at a desktop computer, studying sensitivity data from telescope 2H as it pans slowly across the sky. Outside, visible through the glass doors of this modest office/utility building, are 42 identical dish telescopes, each the size of an apple tree. Only 2H is moving. The orchard’s pattern appears random, with dishes facing all directions. In fact, the arrangement is as random as a computer program can make it.

Tarter writes something down, then goes into an adjoining room to pull one cable from an electronic console and plug in another. Telescope 2H is done; time to test another. If you didn’t know better, you might guess this is the IT department for a satellite radio company, and that Tarter is the head geek. Look around, though, and you’ll see something else is afoot. In the electronics room, one of the refrigerator-size computers sports a bumper sticker with the question, “Are We Alone?” and a Web address for the SETI Institute in Mountain View, California, where Tarter is the director for SETI research, “chief cheerleader” (her words) for the Allen Telescope Array (ATA), and the leading figure in her small and peculiar field of science (as well as a contributing editor of Air & Space/Smithsonian). Paul Horowitz of Harvard, probably the second most prominent SETI-ologist, remarked in 1988: “Jill Tarter has been plugging away at SETI for at least a decade, rebutting bad ideas, going around actually doing SETI on the world’s telescopes instead of talking about it, basically calling everyone’s bluff and keeping the subject from becoming too theoretical.”

To “do SETI,” scientists like Tarter use radio telescopes (usually) to either scan the sky or point at selected sun-like stars, listening for signals that would be recognizably artificial in origin. The rationale is that some extraterrestrial society more advanced than ours, with more powerful transmitters, might be broadcasting a signal—perhaps a series of dots and dashes, or a continuous tone—that would stand out from the natural radio emissions of stars and galaxies. Radio waves are a logical choice for interstellar communication because they cut through the gas and dust between stars. It’s called the search for extraterrestrial intelligence, though it isn’t really. “We look for evidence of somebody else’s technology,” Tarter has said. “I don’t know how to find intelligence.”

She is good-humored and friendly, if slightly brisk in manner, as though constantly aware she’s behind in her work. She likely is: These are busy days.

Tarter has driven the five hours from her SETI Institute office in Silicon Valley to Hat Creek (the license plate of her Saab sedan reads “SETI”) to spend a week running checks on the ATA telescopes. She and her husband, Jack Welch, a radio astronomer at the University of California at Berkeley and a key figure in designing this array, often make the trip in his Cessna 210 to save time. She flies too, but didn’t on this trip.

Tarter worked on her first SETI project, Berkeley’s SERENDIP 1, as a grad student at Hat Creek in the 1970s. She had grown up reading science fiction, and can’t remember ever not believing in the possibility of extraterrestrial life. What prompted her to make it the focus of her career was a 1971 NASA study called Project Cyclops, which outlined a practical approach to building an observatory for radio SETI. Although Cyclops’ array of 1,000 telescopes was deemed too expensive to build, the idea had great appeal to Tarter, and it set her on an unusual course for a scientist, where the chance of getting solid results (an alien signal!) would remain slim, but there would always be plenty of work to do improving detection methods. Like almost every search conducted to date, Tarter’s first venture into SETI 30 years ago had to piggyback on another radio astronomy project. Now, at 63, she finally has a dedicated observatory in the Allen array, like a lifetime renter moving up to buy.

More than 100 SETI searches have been conducted since 1960, with no signal detected. That sounds conclusive, but it’s not. Most searches have been very limited—a patch of sky here, a narrow slice of the radio spectrum there. It’s as though a driver going cross-country had tuned to a single radio channel for a few seconds, heard nothing, tried two more channels the next day, heard nothing, and concluded that the United States has no radio stations.

With Tarter in the lead, the privately funded SETI Institute (Congress cut all NASA funding for SETI in 1993) conducted the most comprehensive search to date, called Project Phoenix, from 1995 to 2004. Phoenix targeted about 1,000 sun-like stars, spending a few minutes listening for radio signals from each. “There wasn’t a transmitter pointed our way when we looked,” says Tarter. “Does that mean there’s no technological civilization? I don’t know. That’s a much harder conclusion to draw.”

Phoenix took 10 years because the SETI-ologists had to borrow observing time, a week here and a month there, on other people’s radio telescopes, including the 1,000-foot-diameter Arecibo dish in Puerto Rico and the 210-foot dish at Parkes, Australia. Tarter’s new array of telescopes will do SETI operations all day, every day. It will also be used by scientists for conventional radio astronomy—Berkeley is partnered with the SETI Institute on the project—but this time, they’re the ones who will be along for the ride.

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