Search for ETs Focuses on 166 "Promising" Signals

By John Roach
for National Geographic News
Updated March 27, 2003
Astronomers searching for signs of intelligent extraterrestrial life wrapped up their mission in Puerto Rico Wednesday to home in on some of the more exciting radio transmission to reach Earth. They collected data on 166 sources, exceeding their original goal of 150.

The astronomers' quick, real-time analysis of the data revealed no evidence of an extraterrestrial civilization, but they will take a more thorough look at it over the next several weeks.

The trip was the culmination of four years of research conducted by SETI@home, a hugely popular distributed-computing project in which more than 4 million people in 226 countries have volunteered their computer's free time to the search for extraterrestrial intelligence (SETI).

"Millions of people around the world have helped get us to the point where we could identify potential targets and take a second look," Bruce Betts, Director of Projects at the The Planetary Society in Pasadena, California, said in a statement. The society is principal sponsor of the project.

"Now the new data will go back to the SETI@home volunteers for more help with this early but critical step in our continuing search for extraterrestrial intelligence," he said.

The volunteers download a screensaver program from the University of California at Berkeley (UC Berkeley) that kicks in when their computer sits idle. The program sorts through chunks of data received from the university via the Internet for unusual radio signals that might be from alien civilizations.

The chunks of data are bits of digitized noise collected by SETI@home researchers who have a special receiver on the National Science Foundation's Arecibo Radio Telescope in Puerto Rico that allows them to "piggyback" on other researchers' use of the telescope.

"We send our data out in what we call work units to the millions of people who use our screensaver program," said David Anderson, a computer scientist and director of the SETI@home project. "It does signal analysis, looking for signals that are not known to occur naturally."

The screensaver then sends back, via the Internet, the most interesting candidates for further analysis by researchers at UC Berkeley. Since the program was started in 1999, the screensavers have sent the university about 5 billion signals worthy of further analysis.

"We've been weeding through all this stuff," said Dan Werthimer, a physicist and chief scientist for the SETI@home project. "We go through and find what is really interesting."

Through a careful analysis of all this information, the SETI@home researchers narrowed the field of candidates to about 150. They scheduled 15 hours of dedicated telescope time beginning March 18 at Arecibo to re-examine these most interesting parts of the sky in the hopes that one of the signals is truly from alien life. The dedicated observing time was interrupted by a need to re-observe a giant solar flare, but resumed March 24.

Roelof Engelbrecht, a SETI@home volunteer in College Station, Texas who freely distributes an add-on feature to the screensaver program called SETI Spy that enables computers to data crunch more efficiently, said he is pleased that the researchers secured dedicated time on the Arecibo telescope.

"So far all observations have been made while piggybacking on someone else's telescope positions, but now it is SETI@home's turn, even if just for a [day]," he said.

In addition to the 166 candidates identified by SETI@home, the researchers also observed 5 extrasolar planetary systems, 35 nearby sun-like stars, 15 nearby galaxies, and 6 candidates from a second SETI Program at UC Berkeley called Serendip (Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations.)

As well as conducting a thorough analysis of the data collected over the past two weeks, the SETI@home volunteers will continue to sort through the data collected by the special receiver on the telescope and send the most interesting candidates to Berkeley for further analysis. The hope is that one day they really will find an interesting signal.

Against the Odds

Werthimer, who headed for Puerto Rico with two other colleagues while Anderson stayed in California to run the computers, is not optimistic that any of the signals are from an extraterrestrial life-form and cautions against people getting too excited. He puts the chance of success at less than 1 percent.

Since becoming involved with SETI 24 years ago, 11 of them using Arecibo's 1,000-foot (305-meter)-diameter telescope, Werthimer has re-examined several promising signals only to find out they were from a passing satellite, random noise, or some other glitch.

"I don't expect to find ET next week," he said in an interview prior to the trip. "But I am optimistic that Earthlings will find ET in the next 100 years." Technological advances, he added, are making SETI searches much more powerful.

Out of the 150 signals that were selected as the most promising candidates, Anderson said that all of them exhibit characteristics that are consistent with random noise. Given that, he too is not optimistic that ET will be encountered.

"It is really hard to put a number to it, but most people feel the odds are quite low," he said.

Nevertheless, the scientists carefully narrowed down the most likely candidates, ranking them based on criteria such as strength, whether or not the signal was detected more than once, and whether or not it is coming from a star known to have planets.

Looking for a Match

As the team re-examined the spots in the sky where the candidate signals came from, they conducted a limited amount of analysis of the data. If something very strong or interesting appeared they would have stopped the search and repeated it to make sure it was not radio pollution or some other kind of noise.

On this most current mission, nothing interesting appeared.

If the scientists do eventually find something that looks exciting, they will ask for independent confirmation of the signal by another group of astronomers using a different telescope and processing software.

"If they see something too, we can measure distance to it, train on it, then make an announcement that we found an interesting signal," said Werthimer.

Richard Factor, president of an organization dedicated to the search for evidence of extraterrestrial life called the SETI League, in Little Ferry, New Jersey is pleased that SETI@home has the opportunity to look at these 150 areas, but agreed that the chances of finding ET on this outing were slim.

"Since they stated that these candidates are about what one would expect from a statistical analysis of receiver noise, I am not unduly optimistic," he said.

Factor is optimistic that chances of finding ET in the future are good, but he is not at all impressed by the 4,287,000-plus people who have downloaded the SETI@home screensaver.

"That's less than one tenth of one per cent of the Earth's population," he said. "I should like to think that SETI is far more important than this indicates."

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