After years of cocking their ears for radio signals from extraterrestrial civilizations, astronomers are now turning their eyes skyward. Private funding for three new low-cost "optical SETI" (Search for Extraterrestrial Intelligence) initiatives was announced this week by The Planetary Society, a space advocacy group in Pasadena, California.
Although most ongoing SETI searches use large radio telescopes, some SETI scientists have been arguing that laser light--both optical and infrared--would actually be a better way for extraterrestrials to communicate. Whereas radio waves travel farther, "lasers are clearly superior for direct, point-to-point interstellar communications out to ranges of several thousand light-years," says Stuart Kingsley, director of the small Columbus (Ohio) Optical SETI Observatory, which began its work in 1992.
Now, three new efforts are mirroring Kingsley's work on a much larger scale. Two of the new programs will scour thousands of stars for patterns in the form of repeated bright pulses lasting as little as a few billionths of a second. One effort, begun last fall at Harvard University's Oak Ridge Observatory in Massachusetts, has thus far watched 849 stars using light from stars that other astronomers are monitoring for planets, says astronomer Paul Horowitz. The second program, with an automated telescope at the Leuschner Observatory of the University of California, Berkeley, will begin regular observations next month, says astronomer Dan Werthimer. In the third effort, also based at UC Berkeley, planet-hunter Geoffrey Marcy and his team will search for steady, bright signals of a single color--another possible means of intelligent broadcast--in thousands of stellar spectra they already have collected.
If scientists do find a signal, says Werthimer, it will likely be one intentionally directed toward Earth. "They would know about us," he reasons. Astronomers acknowledge that any dialogue would be sluggish because of the distance but not impossible, because there are hundreds of sunlike stars within 50 light-years of Earth.
Optical and infrared lasers are "just as promising" as radio signals for extraterrestrial detection, says laser pioneer and Nobel laureate Charles Townes, a physicist at UC Berkeley. "It's time that we looked." Astronomer Guillermo Gonzalez, a SETI skeptic at the University of Washington, Seattle, applauds the scientific approach of the new efforts but adds, "I still think the probability of success for SETI is extremely small."