We've come a long way since 1600, when Giordano Bruno, a defrocked priest from Naples, was burned at the stake for espousing, among other things, his belief that there might be other worlds and other life-forms beyond Earth. In our Star Trekking age, it's now almost heretical not to believe in extraterrestrial life—a belief that will surely be fortified by last week's announcement of the discovery of two Saturn-size planets around two distant stars.

Polls show that 54% of Americans are convinced that there are aliens out there, to say nothing of the significant fraction (30%) who suspect we've already been visited by them.

If there really is life elsewhere in the universe, what are the odds of finding it in our lifetime—or even our children's? Hunting for extraterrestrials, smart or otherwise, requires a lot of faith. You have to believe that conditions for life (liquid water, mild temperatures, protection from lethal radiation) are not unique to Earth; that under the right circumstances, life can arise fairly easily; and that if it does reach a level advanced enough to broadcast its presence, it won't destroy itself in a nuclear war or an environmental meltdown before firing off Earth-bound communiques.

That's plenty of ifs for skeptical scientists to swallow. As physicist Enrico Fermi liked to say, if there are so many extraterrestrials out there, why haven't we heard from them?

To some curmudgeonly types, all this E.T. talk is pretty brainless. Evolutionary biologist Ernst Mayr, for one, considers the likelihood of life of any sort beyond our planet close to zilch. Says he: "The chance that this improbable phenomenon [the creation of life] could have occurred several times is exceedingly small, no matter how many millions of planets in the universe."

Paleontologist Peter Ward and astronomer Donald Brownlee agree. In a provocative new book, Rare Earth, they maintain that in most places beyond Earth, radiation and heat levels are so high, life-friendly planets so scarce and the cosmic bombardments—like the one that killed off the dinosaurs 65 million years ago—so severe that the only life-forms that might make it would be bacteria-like critters living deep in the soil. The odds against technologically advanced societies, they argue, are astronomical.

Surprisingly, even Geoff Marcy, the leader in the increasingly successful hunt for planets outside our solar system, feels that we may well be alone in the universe. Most of the 33 newly discovered planets—giant gas bags all, including those two new ones—swing so erratically around their parent stars that they would create havoc on any smaller, nearby, life-friendly planets.

MORE>>

PAGE 1 | 2