Scientists listening more closely to hear if there's anybody `out there'

Carl Sagan's new novel, ``Contact,'' dramatizes the power of an extraterrestrial message to broaden humanity's perspective. It reflects his conviction that ``the issues that divide us on this planet would tend to wither in view of the need for a proper response'' to a cosmic signal. Such is the hope that inspires the search for extraterrestrial intelligence (SETI). Now a powerful new radio telescope is pursuing this quest. It came on line Sept. 29 at Harvard University's astronomical field station in Harvard, Mass.

This carries forward a search program begun in 1983 by Harvard physicist Paul Horowitz with support from the Planetary Society, of which Sagan is president. Horowitz has characterized that first program -- called Project Sentinel -- as allowing scientists to do as much effective searching in one minute as the earliest SETI programs, beginning 25 years ago, could do in 100,000 years. The new program -- called META, for Megachannel ExtraTerrestrial Assay -- represents a quantum leap beyond that.

Essentially, the searchers are trying to find a radio message against a noisy natural radio background. The quietest part of this radio noise spectrum is in the microwave region, say, from 1 to 300,000 megahertz (MHz). This, presumably, is the frequency range best suited for interstellar communication, and this is where SETI searchers tend to listen.

Radio noise from oxygen and water in our own atmosphere also makes it hard to detect a radio signal above 10,000 MHz. Certain presumably preferred frequencies for cosmic signaling are well below this cutoff, however. The most celebrated is the 1,420-MHz natural radio emission of hydrogen. This frequency would be monitored by astronomers of any technically advanced civilization studying the cosmos. So a radio message beamed at close to this frequency would likely be noticed.

Yet another way to beat the noise problem is to scan the incoming radio waves over a number of narrow frequency channels. This is analogous to a CB scanner sweeping across radio channels on Earth, except that the SETI analyzer listens to all channels simultaneously. The power of natural noise in any one narrow range of frequencies is relatively low, while the strength of a deliberate signal should be relatively high. This, in effect, allows a SETI instrument to tune in on the desired signal.

All of this has to be done swiftly and automatically, whether the SETI telescope is methodically exploring the entire sky or is listening to selected star systems. There is just too much work involved for human operators to attend to. This is what the original Sentinel program did in a search centering on the 1,420 hydrogen frequency. Horowitz attached a 131,000-channel, computer-controlled analyzer to an 84-foot radio telescope antenna that Harvard had declared surplus. His new equipment -- built

with a $100,000 grant from moviemaker Steven Spielberg -- listens to 8.4 million channels over a 350,000-MHz frequency range.

After 25 years of sporadic effort and several dozen listening programs, searchers have yet to detect a recognizably intelligent signal. But these admittedly primitive, preliminary efforts have scarcely begun the immense task of searching all possible signal sources.

Indeed, SETI has only recently begun to be pursued in earnest as a mainline scientific activity. It achieved ``official'' recognition in 1982 when the International Astronomical Union established IAU Commission 51 to look after SETI. Now with META, and an even more powerful National Aeronautics and Space Administration program under way in the United States, plus several efforts elsewhere, the search is proceeding with the kind of continuing, internationally coordinated effort that is needed if it is ev er to succeed.

This is not an especially costly undertaking. META operates on $20,000 a year. NASA's annual SETI budget is about $1.5 million, with the equivalent of 10 full-time staff members. It is developing an analyzer with 10 million channels to cover a frequency range of 1 to 10,000 MHz. These analyzers should be ready for installation by 1988. The program anticipates an all-sky search, plus searches lasting for five to 10 years of 800 solar-type stars within 80 light-years of Earth. Radio telesc opes in several countries, as well as NASA antennas, would be used for this purpose for a few percent of their working time.

No one knows when or whether SETI will succeed. Detection of a signal would be a major turning point in human development. Continued failure may lead us eventually to conclude that, for practical purposes, we are alone. Either way, humanity would make a major advance in self-awareness. Sagan is right. At base, SETI is essentially ``the search for who we are ourselves.''

A Tuesday column. Robert C. Cowen is the Monitor's natural science editor.