Eagerly Seeking Extraterrestrials

Berkeley's SETI Team Gears Up for a New, Expanded Search

by Robert Sanders

After a so-far unsuccessful search through more than 150 trillion radio signals from outer space, one of the longest running hunts for extraterrestrial intelligence is gearing up for a fourth-generation search on the world's largest radio telescope.

Berkeley's SERENDIP project--an acronym for Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations--is now 20 years old and has employed 10 different radio telescopes over the years.

The most recent, third generation search--SERENDIP III--piggybacked on the world's largest radio telescope at Arecibo in Puerto Rico. That search ended last month and the team continues to analyze the catalogued signals. Preliminary analysis, however, showed no likely "intelligent" signals from space.

SERENDIP IV will be up and running on the Arecibo telescope by July, with new instrumentation capable of scanning 40 times more radio bands than the previous equipment.

Besides scanning the sky again but at different frequencies, the team also plans to revisit the most interesting candidates from previous SERENDIP searches.

SERENDIP program manager Dan Werthimer, an astronomer at the Space Sciences Laboratory here, discussed the just-completed four-year search and plans for the new search at a press briefing Feb. 11 at the annual meeting of the American Association for the Advancement of Science in Baltimore. He also delivered a scientific review of the SERENDIP Sky Survey at an afternoon session on SETI searches.

SERENDIP is one of four ongoing SETI (Search for Extraterrestrial Intelligence) projects in the country. Begun in 1977 by Stuart Bowyer, now professor emeritus of astronomy, it is one of the most comprehensive in that it has examined more sky and wavelength bands than all other SETI searches combined.

The SERENDIP team has achieved such coverage by "piggybacking" on the 1,000-foot diameter Arecibo telescope. That is, they share the telescope with other astronomical projects.

This is an advantage in that they can scan the radio band for 24 hours a day.

The limitation, of course, is that they receive signals only from that area of the sky where the telescope is pointing for the primary radio astronomy project.

Despite this limitation, Werthimer said, over the course of four years SERENDIP III was able to scan approximately 93 percent of the sky visible from Puerto Rico, which is about a third of the entire sky.

Nearly half the sky visible from Puerto Rico was surveyed five or more times.

Every few days an interesting radio signal turned up, he said, but "so far, no signal has been so amazing that it sent us rushing to Arecibo seeking dedicated telescope time."

When they do find an interesting signal they will schedule telescope time to double check that region of sky.

Recently they checked out three new planets discovered in the past four months--two of them reported last month by Werthimer's colleagues Geoff Marcy and Paul Butler at Berkeley--but found no unusual radio signals.

"Absence of evidence is not evidence of absence of extraterrestrial civilizations," Werthimer said. "Our civilization is just beginning to develop the techniques, and our capabilities for search are doubling every year.

"Early TV broadcasts from Earth, such as 'I Love Lucy' and 'Ed Sullivan,' have gone past several thousand stars so far. Perhaps SERENDIP will one day intercept another civilization's unintentional leakage, or even an intentional message beamed our way."

The SERENDIP search complements other ongoing searches, such as a private effort based in Mountain View, Calif., which uses a "targeted" strategy. That is, the astronomers look at specific stars rather than scan the whole sky as does SERENDIP.

"It's not clear which is the best strategy, a targeted search of the nearest stars or a whole-sky search for any strong source," Werthimer said.

"It's probably best to do both. We're all just hoping to see something."

At Arecibo, SERENDIP IV will have its own dedicated receiver at a wavelength of 21 centimeters (or a frequency of 1420 MHz, scanning a bandwidth of 100 MHz).

This spot in the radio band is often called the water hole because radio emissions from cool neutral hydrogen and hydroxyl groups--components of water--are seen in this region of the spectrum.

Many people think this radio band is the most promising spot to look for extraterrestrial signals, since radio waves in this band are not absorbed or attenuated much as they traverse the universe.

The new instrumentation consists of 40 signal-analyzing circuits, synchronized and controlled to examine 168 million channels every 1.7 seconds.

The circuits automatically filter out radio frequency noise, which dominates the band, and other signals like those from radio pulsars, in search of strong radio signals that could indicate an intelligent origin.

SERENDIP III scanned the heavens in a 12MHz band centered around 429 MHz, examining 4.2 million channels every 1.7 seconds. The circuitry built by the Berkeley group has been adopted by several other SETI groups in search of intelligent signals.

The group in Mountain View uses circuits built by Werthimer and his colleagues at the Space Sciences Laboratory, while the Harvard SETI group built circuits based on the Berkeley design.

SERENDIP is funded by the Friends of SERENDIP, a group of private donors headed by science writer Arthur C. Clarke, and by the Planetary Society, an international non-profit organization headed by astronomer Carl Sagan. The Arecibo telescope is operated by the National Astronomy and Ionosphere Center.


Copyright 1996, The Regents of the University of California.
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