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Hey, E.T.! The line is open

SETI Institute
Radio dishes monitor the skies over California at the Allen Telescope Array.

After years of preparation and testing, the SETI Institute has released the first results from a search for alien signals that uses the $50 million, 42-dish Allen Telescope Array. You didn't hear about it? Maybe that's because none of the thousands of signals picked up so far has rung an alarm bell.

Nevertheless, the fully functioning system represents the latest, greatest leap in the nearly 50-year-long search for extraterrestrial intelligence, or SETI.

The Allen Telescope Array was conceived more than eight years ago, and it's been two years since the system's switches were flipped on in a remote valley near Mount Shasta in Northern California. Scientists have been tinkering with the equipment and testing the software since then. Finally, on May 28, astronomers kicked off regular rounds of SETI surveys, seven hours a day, roughly four to five times a week, according to Peter Backus, the SETI Institute's manager of observing programs.

Backus said the significance of the milestone sank in a couple of days later, when he and other members of the research team were sitting around a table for a planning meeting.

"We just looked at each other and said, 'Hey, we're actually observing again!' It was a great feeling for the whole gang," he told me.

Initial results from the SETI survey, as well as from seven other experiments conducted using the telescope array, were presented during poster sessions at this week's meeting of the American Astronomical Society in Pasadena, Calif.

From big to little dishes
Astronomers have been looking for alien radio signals since 1960, on the assumption that extraterrestrial civilizations would try communicating over light-years of empty space the way we might communicate with them. The trick is to identify signals that have the earmarks of an artificial source - but originate from deep space rather than from Earth or our own satellites.

The SETI Institute's scientists have used several big radio dishes to do this work - including the Green Bank Telescope in West Virginia and the Arecibo Observatory in Puerto Rico. But they've had to wait in line along with other radio astronomers pursuing more, um, conventional research goals. At Arecibo, for example, the institute's Project Phoenix was allotted 2,400 hours of telescope time over the course of five and a half years.

In 2001, the SETI Institute went ahead with plans to build a radio telescope of its own, in league with the University of California at Berkeley. Private benefactors, led by software billionaire Paul Allen, kicked in millions of dollars to get the ball rolling.

Unlike Arecibo, the Allen Telescope Array is composed of 42 separate dishes, each one 20 feet (6.1 meters) wide, which are networked together with software to create an observatory with the sensitivity of a single 133-foot-wide (40-meter-wide) dish. Eventually, astronomers hope to expand the array to 350 dishes.

The array can be configured to target multiple spots on the sky simultaneously, or take readings for different experiments at the same time. For example, while the SETI Institute team looked for alien transmissions from the central region of our galaxy, Berkeley astronomers could check the same area for naturally occurring transient radio sources.

Here's how the SETI watch works:

  • The telescope is aimed at two separate target spots for 98 seconds at a time. The software looks for pulsed, continuous signals that stand out from the static of space, as I explain in this archived audio clip. Such signals are checked against a database of previously detected, human-created radio transmissions. The signals that aren't in the database go on to the next round.
  • If the exact same signal is detected at both target locations, that's a sign of terrestrial interference. Sorry, no E.T.
  • If the signal emanates from only one of the targets, then the telescope shifts its beam slightly off-target. If the signal is still detected, it's not from a faraway source. Again, no E.T.
  • If the signal passes this first on-off test, the cycle is repeated a second time to see if the pattern persists. If the signal looks promising, then it's time to tell other astronomers to take a look and offer a second (or third, or fourth ...) opinion.

On one night last week - June 3, to be exact - the system picked up a total of 8,616 signals to check. More than 90 percent of those were eliminated right away because they were matched up with the database of previously known signals. Just 180 of the remaining signals hung around long enough for further checking. The "same signal from two places" test eliminated all but two of those signals. The first on-off test eliminated one of those two, and the second on-off test eliminated the other one.

Bottom line: a big fat zero.

Searching while humans sleep
Watching all this happen might be an exercise in disappointment. So maybe it's a good thing that all this takes place automatically, without a human tracking the hopes as they're dashed nightly.

"The 'carbon-based units' are blissfully asleep," Backus said. "At 8 o'clock in the morning, we get an e-mail."

Another plus is that the researchers don't have to sleep on cots at the telescope site. The SETI search, like most astronomy projects nowadays, can be monitored remotely.

"A couple of weeks ago I was doing some engineering tasks in the predawn hours - in my pajamas, at my home computer," Backus recalled.

In any SETI quest, so many earthly signals are picked up that astronomers have gotten used to the routine of eliminating the possibilities until nothing is left. "When we have a system that is sensitive to [radio] sources that are light-years away, it's easy to pick up something from just down the street," Backus said.

The nice thing is that astronomers now have the power to tinker and tweak their own telescope to optimize the search. Eventually, they'll be doing SETI seven days a week, 24 hours a day. "We're happy to refine the procedure as we learn," Backus said.

And one of these days, those astronomers just might get a computerized e-mail that doesn't have a big fat zero on the bottom line. Then what?

Feel free to chime in with your comments below, and click the links to read bygone tales from the SETI quest:

... And here's a roundup of the Cosmic Log items from this week's AAS meeting:

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