Is there anybody out there?
Off and on during more than three decades, scientists have analyzed radio signals from space in the hope of uncovering evidence of extraterrestrial life. But the new radio survey, though it can only detect signals from nearby stars, has a million times the sensitivity of previous studies, says David Brocker, project manager for SETI (Search for Extraterrestrial Intelligence) at NASA's Ames Research Center in Mountain View, Calif. Brocker says that the new search gathered as much data in the first five minutes of operation as previous searches had in the past 32 years. Thanks to high-speed supercomputers, he adds, the data are analyzed in "real time"--while they're being collected. This allows researchers to immediately identify and conduct followup observations of intriguing radio signals.
The 10-year international survey features two key studies.
At the Arecibo Observatory in Puerto Rico, scientists have begun using a 1,000-foot-wide, dish-shaped antenna -- the world's largest radiotelescope -- to record microwave signals from individual stars. The signals bounce off the antenna to a system of amplifiers and frequency converters suspended above it. From there, they travel down to a huge trailer that houses processing equipment, including a spectrometer that can analyze the polarization, intensity, and duration of radio waves in the frequency range of 1 to 3 gigahertz.
This configuration of amplifiers and analyzers, which will initially search for telltale radio signals from 40 stars within 80 light-years of Earth, will remain at Arecibo only until Nov. 20, when it will have to make way for a planned upgrading of the radiotelescope. Moving to the Parkes Radio Observatory in Australia, the system will study radio emissions from stars that can only be detected from the southern hemisphere. Researchers expect that mobile signal-analyzing systems will eventually be coupled with four observatories, including a return visit to Arecibo in 1995.
Simultaneously with this "targeted" search of individual stars, Brocker and his colleagues have begun using NASA's 112-foot Goldstone radio antenna in the Mojave Desert to scan, at lower sensitivity, small patches of sky. The scanning survey can detect only continuous beams of radio waves, in contrast to the targeted searches, which can also detect radio pulses. However, scanning does offer the advantage of receiving emissions from many stars at once and, over time, surveying the entire sky.
Researchers looking for extraterrestrial activity focus on microwaves, notes Brocker, because stars usually emit little radiation at these wavelengths. With less of our galaxy's background noise to contend with in this "quiet zone" of the electromagnetic spectrum, scientists can more easily pick out alien messages. Such signals may include extremely narrow frequency bands of radiation that atoms don't emit naturally, as well as high-intensity pulses.