SANTA CLARA, Calif. ? Proof ofextraterrestrial intelligencecould come within 25 years, an astronomer who works on the search saidSunday.

"I actually think the chances thatwe'll find ET arepretty good," said Seth Shostak, senior astronomer at the Search forExtraterrestrial Intelligence Institute in Mountain View, Calif., hereat the SETIcon convention. "Young people in the audience, I thinkthere's areally good chance you're going to see this happen."

Shostak bases this estimation on the DrakeEquation, a formula conceived by SETI pioneer Frank Drake tocalculate thenumber (N) of alien civilizations with whom we might be able tocommunicate.That equation takes into account a variety of factors, including therate ofstar formation in the galaxy, the fraction of stars that have planets,thefraction of planets that are habitable, the percent of those thatactuallydevelop life, the percent of those that develop intelligent life, thefractionof civilizations that have a technology that can broadcast theirpresence intospace, and the length of time those signals would be broadcasted.

Reliable figures for many of thosefactors are not known,but some of the leadersin the field of SETI have put together their best guesses.Late greatastronomer Carl Sagan, another SETI pioneer, estimated that the DrakeEquationamounted to N = 1 million. Scientist and science fiction writer IsaacAsimovcalculated 670,000. Drake himself estimates a more conservative 10,000.

But even if that lower value turnsout to be correct, at therate they're going, it wouldn't take scientists too long to discover analiensignal, Shostak said.

"This range, from Sagan's milliondown to 10,000 ? that'sthe range of estimates from people who have started and worked onSETI," saidShostak. "These people may know what they're talking about. If they do,then the point is we trip across somebody in the next several dozen ortwodozen years."

The SETI quest is set to take a leapforward when the AllenTelescope Array, a network of radio dishes under construction innorthernCalifornia, is fully operational. By 2015, the array should be able toscanhundreds of thousands of stars for signs of extraterrestrialintelligence,Shostak said.

But while humans might be able todiscover an alien signalwithin that timeframe, interpreting whatET is trying to tell us could take much, much longer.

Shostak admitted such a task would bevery difficult. Analien civilization may be as technologically advanced compared to us asHomosapiens are to our hominid relatives Neanderthals.

"We could give our digital televisionsignals to theNeanderthals, and they?ll never figure it out. And they're not stupid,"hesaid.

Yet simply having proof that we arenot alone in theuniverse would likely be a world-changing achievement, Shostak added.