Scientists listening for radio signals from intelligent beings on other planets say they are not discouraged by the latest results from the four biggest searches now under way.
So far, nobody's home. But writing off the enterprise now as worthless, they said, would be like giving up on Christopher Columbus because he reported, a few days after leaving Spain, that he had found "just water."
Dr. Jill Tarter, speaking in Baltimore at the 1996 meeting of the American Association for the Advancement of Science, said that with 100 billion sunlike stars to examine in our Milky Way galaxy alone, it would be generations before science could say the search was fruitless.
"I think it will succeed, but it may be my granddaughter who finishes it," said Dr. Tarter, who is director of Project Phoenix, a search program at the SETI Institute in Mountain View, Calif. SETI stands for Search for Extraterrestrial Intelligence.
Using private money
Search team members say that, despite the 1993 loss of federal support, they are continuing with private money to develop new high-technology ways to vastly expand the scope and speed of the search.
They are even planning how to notify the world when the first extraterrestrial signal is received, and how to respond to it.
This is radio astronomy. While other astronomers study the sky by looking at visible portions, SETI scientists are searching with their ears, scanning frequencies for signals not generated by man.
More specifically, they have chosen frequencies where the stars and galaxies are fairly quiet and that travel across vast distances without being absorbed by interstellar gas and dust.
They are guessing that other civilizations would pick this same "clear line."
Radio telescopes are basically pointable antennas. Like optical telescopes, they can be aimed at specific stars, or programmed to scan a narrow strip of sky as the Earth turns.
The SETI Institute's six-month investigation of 200 nearby, sunlike stars found many "intelligent" signals. But all of them turned out to be interference from Earth's own technology.
Every day, for example, radio astronomers in Australia picked up a feeble signal from well outside our solar system. It turned out to be the Pioneer 10 spacecraft. Launched in 1972 to photograph the planet Jupiter, it is now 6 billion miles out, 1 1/2 times the distance to Pluto. Its transmitter, about as powerful as a flashlight, is still working.
The SETI Institute is a direct descendant of NASA's own SETI project, which Congress ended after just four years in 1993.
Reorganized as the SETI Institute, the project has since managed to attract $15 million in private donations to extend the search for at least five years.
Aiming at stars
It is the only SETI program that aims at likely stars. Programs at Harvard University, the University of California at Berkeley and Ohio State University are doing broad sky surveys -- all without a discovery so far.
Last February, using a pair of radio telescopes in Australia, Project Phoenix began studying 200 stars of about the same age, size and temperature as our sun. All are close neighbors -- within 150 light years of Earth.
The scientists searched for signals in 28 million narrow-band radio channels at a time, covering about 2 billion channels for each star system in a half-day. A similar search by inhabitants of a planet circling the nearest of those stars, Dr. Tarter said, would detect Earth's radars.
The Australian telescopes sorted the radio signals by computer, rejecting any that had been seen before. Any new "hits" on one telescope were compared with data from the second telescope 200 miles away. Only a signal originating in the heavens would turn up strongly on both.
On fewer than 100 occasions the computers called for human help. Each time, the signal turned out to be terrestrial.
"There are no mysteries; no evidence of technologies around any of these stars," Dr. Tarter said.
Project Phoenix is continuing the search, with 800 more stars on its search list.
"If we're not successful, we'll go on to a larger target list," Dr. Tarter said.
She hopes to expand the search to a million stars in the next decade. That will require larger telescopes and improved signal processing. Project Phoenix hopes to establish a $100 million endowment to pay for the work.
In the meantime, the International Institute of Space Law, and the International Academy of Astronautics have prepared a "white paper" for presentation next summer to the United Nations' Committee on the Peaceful Uses of Outer Space. The paper raises questions about whether and how such a signal might be answered, and by whom.