The greatest search of all will begin so quietly that it will seem almost timid.
Next week, 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."
Monday, the 500th anniversary of Columbus' discovery of the New World, the National Aeronautics and Space Administration will finally begin its "Search for Extraterrestrial Intelligence."
The $100 million project is scheduled to be financed 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 past three decades during its first minute of operation.
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 away 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 with Frank Drake, then a young scientist who was pioneering in the field of radio astronomy.
Mr. Drake, now 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 radio telescope was being built there, and Mr. Drake's task was to help decide how best to use it.
Many stars emit radio waves, and if human ears were tuned to the right frequency the sky would roar as much as it glows. As he studied the new telescope, Mr. 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.
The telescope was hooked up to loudspeakers so Mr. Drake could hear any signals coming from two nearby stars.
Others joined in the effort, most notably Paul Horowitz of Harvard University and the Pasadena, Calif.-based Planetary Society. So far, no one has succeeded, but there have been several dozen tantalizing signals that "had all the right earmarks," Mr. Drake said. None have been confirmed by a second observation.
The search so far has been 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.
The search will change dramatically Monday when scientists, for the first time, will be able to listen to every frequency.
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, 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 then 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," Ms. Tarter said.
If everything adds up, the computers "will sound the alarm," said Ms. Tarter, the project scientist.
"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 the signals are out there, and if the NASA program fails, it will only be because the search was flawed.