BERKELEY – After more than a million years of computation by more than 4 million computers worldwide, the SETI@home screensaver that crunches data in search of intelligent signals from space has produced a list of candidate radio sources that deserve a second look.
Three members of the SETI@home team will head to Puerto Rico this month to point the Arecibo radio telescope at up to 150 spots identified as the source of possible signals from intelligent civilizations.
SETI@home is a computer program disguised as a screen saver that pops up when a computer is idle and analyzes radio telescope data in search of strong or unusual signals from space. The candidates for re-observation are particularly strong signals or ones that have been observed in the same spot more than once, some of them five or six times.
"This is the culmination of more than three years of computing, the largest computation ever done," said UC Berkeley computer scientist David Anderson, director of SETI@home. "It's a milestone for the SETI@home project."
SETI@home users should find out the results of the re-observations - what The Planetary Society, the founding and principal sponsor of SETI@home, is billing as the "stellar countdown" - within two to three months.
Though excited at the opportunity to re-observe as many as 150 candidate signals, Anderson is cautious about raising people's expectations that they will discover a signal from an extraterrestrial civilization.
"If there is any possibility at all of finding an extraterrestrial signal, it's probably much less than one percent," he said.
UC Berkeley physicist Dan Werthimer, SETI@home chief scientist, isn't getting his hopes up, either. He has conducted a Search for Extraterrestrial Intelligence (SETI) for 24 years - 11 years using Arecibo's 1,000-foot diameter radio dish - and has returned several times to look again at promising locations and frequency ranges to determine if a strong radio signal is more than random noise, a glitch or a passing satellite. He has been disappointed each time.
On the other hand, SETI@home has mobilized so much more computing power than has ever before been thrown at signal analysis, that the team has been able to perform much more detailed and complicated computations on the radio data than now possible with Werthimer's ongoing SETI project, called SERENDIP IV (Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations).
"I give it a one in 10,000 chance that one of our candidate signals turns out to be from ET," said Werthimer, who will head for Puerto Rico on March 16.
"Whether or not SETI@home succeeds in finding evidence of extraterrestrial intelligence at this early date, this project has already made history," said Bruce Murray, chairman of The Planetary Society's board of directors. "SETI@home has performed the most sensitive and detailed SETI sky survey to date, has demonstrated the power of the Internet for doing scientific distributed computing, and has allowed the general public to participate directly in an exciting research project."
To acknowledge the 4,287,000-plus users who have analyzed radio data, the SETI@home team will post on its Web site the names of those participants who flagged the candidate signals as a result of data analysis on their home computers. Each candidate signal was analyzed by several people, because SETI@home sends the same data to more than one person to double-check results.
The list of candidates is far longer than 150, but Werthimer suspects that 150 is the maximum he and two colleagues will be able to observe during the 24 hours total available to them at Arecibo Observatory on Mar. 18-20. Criteria for inclusion in the list include not only a strong radio signal and a signal observed more than once in the same spot and frequency range, but also the signal's proximity to a known star and whether that star is known to have planets.
"These factors let us estimate the probability that a candidate is noise," Anderson said. "We're interested in the candidates that are least likely to be noise."
Limited analysis of the signals will be done while the team collects the data, so that observations can be halted and repeated if a very strong signal reappears. Werthimer will be assisted by graduate student Paul Demorest and project scientist Eric Korpela.
A more detailed analysis will be conducted later, Anderson said, ideally with a new version of the SETI@home screensaver based on a new distributed computing platform called BOINC (Berkeley Open Infrastructure for Network Computing).
SETI@home offered its screensaver to the world in May 1999 as the first example of wide-scale distributed computing - linking idle computers through the Internet to tackle large computational problems. The key to its success was a fruitful collaboration between Anderson, a computer scientist who was one of the principal developers of distributed computing, and Werthimer, a physicist with two decades of experience collecting radio data and parsing it in search of unusual signals from space.
Together, they have drawn in not only sci-fi fans and computer geeks, but many others interested in offering use of their computer to benefit worthwhile projects. SETI@home has spawned numerous other distributed computing projects, including Folding@home to calculate the three-dimensional structure of proteins and climateprediction.net to improve scientific forecasts of 21st century climate.
However, scientists interested in launching similar projects have been daunted by the time and money needed to create the software. To address this problem, Anderson developed BOINC, which is funded by the National Science Foundation. In addition to being a general purpose platform, it allows users to partition their computer time among several distributed computing projects.
"BOINC makes it easy for scientists to set up new SETI@home-type projects, and to update their applications on the fly," he said. "Each change to SETI@home required all our users to download and install a new program version, but BOINC manages this process without user intervention."
BOINC also has the capacity to store data in participants' unused disk space, much the way Napster, Gnutella and Kazaa take advantage of PC hard drives to store MP3 music files.
"The amount of unused disk space out there is staggering," Anderson said. "BOINC will let us experiment with new ways of handling data, like sending it through high-speed Internet connections straight from telescopes to PCs and archiving it redundantly on PC disks. This will greatly expand the scope of our SETI research."
The test case for BOINC is Astropulse, which is designed specifically to re-examine SETI@home data in search of short radio pulses, something neither SETI@home nor any other SETI project currently can do very well. According to Werthimer, Astropulse can detect pulsars, which blink on and off at periods up to nearly a millisecond; evaporating black holes, which should emit a brief pulse of radio waves as they blink out of existence; as well as messages from extraterrestrials.
"Astropulse will be the first big test of BOINC," which also provides enhanced, more realistic 3-D graphics, Anderson said. "If we get maybe 1,000 people participating in the first BOINC trial, we could analyze the re-observation data in just a few days."
"This is a whole new way to look for ET," Werthimer said.
He and Anderson emphasize that, while the re-observations are the culmination of nearly four years of data crunching, SETI@home is not coming to an end. Werthimer hopes to set up a southern hemisphere SETI program at Parkes Observatory in Australia, the data to be fed into SETI@home. And data still comes in from the SERENDIP IV instruments on the Arecibo dish, which will soon use upgraded receivers to record data from more than one area of the sky at once.
"This is a milestone, but SETI@home will go on," Anderson said.
In addition to The Planetary Society, other major funders include Sun Microsystems, the University of California, Quantum Corp., Fujifilm Computer Products and Network Appliance.
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