LISTENING FOR ALIENS

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IF E.T. IS OUT THERE, TRYING TO GET IN touch with us, his message may well be received first in a quiet rural setting 30 miles northwest of Boston. There, atop a hill overlooking a snow-covered apple orchard and the frozen remnants of a pumpkin patch, a dish-shaped antenna, 84 ft. across, faces skyward, attuned to the murmurings of the cosmos.

That antenna is a Harvard-Smithsonian radio telescope, the Brobdingnagian ear of the newly dedicated project BETA, the latest and most ambitious effort yet in the Search for Extra-Terrestrial Intelligence (SETI). The search has been doggedly conducted over 31/2 decades by small bands of devoted scientists around the world. It's a quest not only for life beyond the Earth but for life intelligent and capable enough to transmit meaningful radio signals across vast stretches of empty space.

Inside BETA's one-story control room, a workstation displays patterns of green and red spikes; lights blink on a bank of small computers; and needles flutter on glowing dials. From a stereo amplifier comes a static-filled hiss, the audio version of radio waves piped directly from the antenna above. The display amuses graduate student Darren Leigh, hard at work debugging a BETA computer program. "We do a few things here for the tourists," he explains. "Camera crews love this stuff."

Indeed, most of that light and sound show is superfluous because BETA is, with good reason, an almost entirely automated experiment. Otherwise, as BETA director and Harvard physicist Paul Horowitz puts it, "what do you do when something comes in the middle of the night and there's no one here to listen?"

Each day, as the Earth turns, the BETA (for Billion-channel Extra-Terrestrial Assay) telescope sweeps a circular swath through the heavens, elevated at a slightly different fixed angle from the horizon with each successive turn. During each circuit it captures radio waves reaching Earth at frequencies between 1400 and 1720 megahertz--a broad but relatively "quiet" region of the radio spectrum. "In the 1960s we were looking in a few niches and hoping the extraterrestrials had put their jewels there," says astronomer Frank Drake, who launched the first SETI project in 1960. "They didn't. Now we are doing it right."

Every two seconds, BETA captures enough data to fill a CD-ROM, which adds up to roughly 22 million megabytes of data per day--an overwhelming volume far beyond human capacity to comprehend and evaluate. For that reason, the incoming radio waves are digitized and read into a custom-made, homegrown supercomputer, designed and assembled by Horowitz and his students, that sorts through the input and discards cosmic radio "noise."

Should BETA spot a signal that seems to meet the programmed criteria for artificiality, the radio telescope would abandon its fixed position and automatically leapfrog farther west so that the same sector of sky would pass before it again. If the suspect signal should then reappear in the same location, Leigh says, "alarms won't go off, but the computer will send us E-mail." And unlike earlier SETI programs, which sometimes signaled "hits" that after much excitement and analysis turned out to be beeps from prosaic Earthbound or orbiting electronic sources, BETA methodically compares signals from space to signals from the horizon so it can better differentiate between E.T.'s transmissions and our own.