NASA Holds Its Breath and Listens for Other Worlds : Astronomy: A $100-million project using a powerful computer will monitor millions of radio frequencies.

The greatest search of all will begin so quietly that it will seem almost timid.

Next Monday, a handful of scientists in California and Puerto Rico will flip a few electronic switches and turn on a powerful computer. And then they will listen, for decades perhaps, for some sign, some distant signal from some unknown culture that will tell us that we are not the only creatures who have stared in awe at the night sky and wondered if anyone else was out there.

For centuries, humankind has dreamed of answering that question and for more than three decades scientists have tried, although not with the resources that the challenge demands.

Now, says Jill Tarter, project scientist for the expedition, “We are going to do billions of times more searching than has been done before.”

It is odd that it has taken so long to get this far, because the answer--whatever it turns out to be--will affect everything that human beings think about themselves and their role in the universe. Either we are the only creatures with the intelligence to pose the question, and the meaning of life is ours alone, or there are others, perhaps billions, of civilizations that have traveled this same path.

On the 500th anniversary of Columbus’ discovery of the New World, the National Aeronautics and Space Administration will finally begin its “Search for Extraterrestrial Intelligence (SETI).” The $100-million project is scheduled to be funded until at least the year 2001, and unlike past attempts by a few bold souls with severely limited options, this will be a major scientific endeavor that will surpass the efforts of the last three decades during its first minute of operation.

There will be no ships leaving port or rockets blasting off from their launch pads, to carry these adventurers to new lands. Instead, they will do what humans sometimes seem to do so poorly. They will just listen.

The night sky is ablaze with trillions of stars scattered over distances so vast that it defies human understanding. The nearest star is so far that it takes four years for its light, traveling at 186,000 miles per second, to reach Earth. How many of those stars have planets that could support life? No one knows, but recent evidence suggests that planets have formed around stars, so there may be many other worlds out there waiting to be discovered.

Finding them, however, is one of science’s most daunting challenges.

It is a critical issue because the greater the number of planets, the greater the chances of life existing elsewhere.

The genesis of NASA’s project began many years ago when Frank Drake, then a young scientist who was pioneering in the field of radio astronomy, came up with an intriguing calculation. Since his early childhood, Drake had been hooked on the idea of finding life on other planets.

“In those days, there were no prospects for finding other creatures,” he said recently as he discussed his early years at UC Santa Cruz, where he teaches astronomy.

“But I always had it in the back of my mind, and whenever I dealt with some kind of instrument I would think, ‘Could this be used to detect another civilization or world?’ ” The answer, he said, was always the same: No.

Drake, 62, was one of the first astronomers sent to a new facility that the National Science Foundation was constructing in 1960 in Green Bank, W.Va. The first large radiotelescope was being built there, and Drake’s task was to help decide how best to use it.

Many stars emit radio waves, and if humans could tune in to the right frequency the sky would roar as much as it glows. As he studied the new telescope, Drake came across a startling conclusion.

The 85-foot-wide antenna was so large that if it were on a planet circling a star a few light-years away it would be powerful enough to detect faint signals from television stations on Earth. So it ought to be able to pick up similar signals coming from planets orbiting other nearby stars.

Drake finally had the instrument he had been searching for.

He launched a historic project called Ozma, named for the “queen of the imaginary land of Oz, a place very far away, difficult to reach and populated by exotic beings.” The telescope was hooked up to loudspeakers so Drake and his colleagues could hear any signals coming from two nearby stars, and the experiment had barely begun when they heard noises from the sky that had never been heard before.

But subsequent experiments determined that the signal was some kind of earthbound interference, a common problem whose source is usually identified. Drake never learned for certain what generated the false alarm, but he believes it was some sort of airborne jamming system being tested by the military.

It was a stunning disappointment but perhaps a fitting beginning for an endeavor that would be plagued by false alarms.

Others joined in the effort, most notably Paul Horowitz of Harvard University and most recently the Pasadena-based Planetary Society. So far, no one has succeeded, but there have been several dozen tantalizing signals that “had all the right earmarks,” Drake said. None have been confirmed by a second observation.

The search so far has been severely limited because no one knows which stars to study, and there are literally millions and millions of radio frequencies. Researchers have had to pick certain “magic frequencies” that they think extraterrestrials would most likely use.

First, some scientists concentrated on the frequency of hydrogen atoms, which emit readily identifiable signals, then most others looked at the frequency between hydrogen and oxygen, but apparently that too was the wrong place.

The search will change dramatically Monday when scientists, for the first time, will be able to listen to every frequency.

Tarter, of NASA’s Ames Research Center in Mountain View, has learned how to ignore the “snicker factor” that is a constant threat in the search for extraterrestrial intelligence. Perhaps partially because of that factor, NASA recently renamed SETI the High Resolution Microwave Survey.

For years the project was a favorite target of the late Sen. William Proxmire, but the Wisconsin Democrat was finally won over by astronomer Carl Sagan. Congress still threatens to kill it every now and then, but funding has been adequate in recent years to build most of the equipment needed for the task and the project appears to be in a strong position.

NASA will use its Deep Space Tracking Station in the Mojave Desert to sweep the entire sky over the Northern Hemisphere. Later, facilities in Australia will be added to cover the Southern Hemisphere. In addition, the world’s largest radio dish, at Arecibo in Puerto Rico, will concentrate on about 1,000 nearby stars that are most like the sun and thus believed to be most likely to have planets with intelligent life.

Every frequency from one to 10 gigahertz, the entire radio “window” that reaches the surface of the Earth, will be monitored.

Powerful computers will automatically lock the antennas on whatever signals are received, and run tests to see if the signals really seem to be coming from a distant star. They will look mainly for signals “that technology can produce but nature doesn’t,” Tarter said.

A signal from an extraterrestrial source should also be affected by the Earth’s orbit, thus fixing its position among the stars and giving it a very distinct signature. The computers will automatically switch the telescope on and off the target. If the signal disappears when the telescope is aimed in another direction, its origin would most likely be the celestial suspect.

If everything adds up, the computers “will sound the alarm,” Tarter said.

Astronomers around the world will be alerted in hopes that other telescopes might confirm it. If independent observations support the discovery, Tarter said, NASA will call a news conference.

“We will announce it,” she said. “I want to make that clear,” she added, concerned over suggestions by some that the discovery would be so troubling that the military would classify the results.

Official statements are filled with warnings that the search may take generations to complete and they talk publicly about long odds and whether they will succeed, but most of the scientists involved in the effort are true believers. They think they are really out there, and if the NASA program fails, it will only be because the search was flawed.

Because the sun is a middle-aged star, Drake believes that about half of the other civilizations will turn out to be more advanced than our own because they will have had millions or even billions of more years to grow.

That has given rise to a tantalizing scientific debate led by mathematician Frank Tipler of Tulane University. He has argued that any advanced culture would inevitably embark on explorations of the universe.

Tipler has worked out mathematical calculations showing that if they proceeded from one star and moved on to the next, no matter where they started in the Milky Way Galaxy, it would take only about 30 million years for an advanced society to colonize the entire galaxy. Because some civilizations would presumably be billions of years ahead of ours, Tipler says, they should already be here, if indeed they exist. And since they are not here, they must not exist.

Sagan has performed the same calculations in a different way and concluded that it would take 5 billion years, not 30 million, for one civilization to colonize the entire galaxy.

“So Sagan’s conclusion is they shouldn’t be here yet,” Drake said with a chuckle, “but any day now. . . .”

Like most people involved in the search, however, Drake doubts that any civilization would be able to colonize the galaxy. The distances between the stars are so great that even the most advanced technologies would probably find it too impractical and costly, he said.

“The cost (of supplying a large rocket) to colonize a star 10 light-years distant (about 60 trillion miles away, a neighbor in celestial terms) in a reasonable period of time is equal to the total energy production in the United States for the next 100 years,” he said. “That’s just basic physics.”

The radiotelescopes used in NASA’s search will be powerful enough to detect microwave transmissions, like television broadcasts or defense radar systems, from planets around nearby stars. Since television transmitters send their broadcasts out in all directions, some of these signals also leave the Earth. That lost signal, called “leakage,” carries our culture out into space.

It may be that other civilizations also have “leakage,” but it may only last a brief period during their cultural evolution. Drake noted that fiber-optics and cable systems are reducing the reliance on transmitting towers, and radar systems are growing obsolete with the reduction in tensions between the superpowers.

“Those systems only lasted 40 years,” Drake said. “If you go to fiber-optics, there will be no energy sliding off into space and so you become invisible.

“For brief periods you are shouting your existence to the universe, and then you stop shouting.”

Always the true believer, he added: “There are a lot of civilizations out there that are way advanced over what we are, but they release almost no signs of their existence. That’s why it’s possible that civilizations are hard to detect even though there are lots of them out there.”

He gives the NASA project about a “50-50 chance” of succeeding.

The need to find other civilizations, he said, “differs from one person to the next,” but “for everybody, there is some philosophical component. The learning of what other intelligent creatures are like aids you in understanding the significance of human beings and their place in the universe. Why are we here, what may we become? What is moral, what is good?”

In her office in Northern California, Tarter also ponders such thoughts.

“It’s the inevitable conclusion of the Copernican Revolution,” she said. “We’re finally getting ourselves out of the center of everything. We are used to thinking about ourselves as being the top of the heap. And we may find that there are others that are more advanced than we are. That may upset some people. It may inspire others.”

Such a momentous discovery would have such widespread implications that NASA has even taken the unprecedented move of consulting with religious leaders to learn more about how humans would deal with discovering that they are not unique.

“We had someone from the Vatican come and do a study, and he summed it up very clearly as he was leaving,” Tarter said.

So quietly it could barely be heard, she said that the searchers, according to the Vatican emissary, are “looking for God.”