Waterworld.(geology of Mars)

Bill Boynton was a young, hotshot scholar of Mars, with his first child on the way, when he got his Big Idea. It was a plan for finding out whether Mars was a barren, dry husk of a planet or was concealing in its soil what were once vast, possibly life-supporting oceans. Boynton proposed a high-tech version of the diviner's rod; all he had to do was persuade NASA to put his instruments on one of its Mars probes. It finally happened in 1992, when his daughter was in second grade, but after an 11-month flight through the solar system the spaceship blew itself to bits. He got a second chance in 1999, when his daughter was a sophomore in high school, on the Polar Lander. It flew all the way to Mars--then crashed. In April 2001 he watched a Delta II rocket carry NASA's Odyssey probe, with his instruments onboard, up into the sky. Mission control lost radio contact with the ship. "My colleagues had been telling me, 'Why don't you just give up, Bill?' and I was beginning to think they were right," he says. "I didn't breathe for about half an hour."

Boynton was third-time lucky. The probe continued on to Mars and by March was beaming back data. The divining rod was pointing most definitely to water--gobs of it. "We've found the equivalent of Lake Michigan twice over," says Boynton. Scientists had already seen signs that water long ago sloshed around on the Martian surface. The Global Surveyor probe, launched in 1996, is still sending snapshots of gullies and canyons that bear a striking resemblance to water-carved features on Earth. But where had all the water gone? Now it seems it's been right there all along, frozen just below the surface. The news, announced last week in the journal Science, came just in time for his daughter's high-school graduation. "I've always tried to teach her the importance of stick-to-it-iveness," Boynton says.

The findings put the solar system in a new light. Mars has always been a likely candidate for harboring extraterrestrial life. Now the odds have improved. That's because when it comes to life, the wetter the better. Odyssey has found water not only at the poles but also a fair way toward the equator. And even though its scanners penetrate only about a meter below the Martian surface, to that depth they've found higher concentrations of water than anybody expected; half to three quarters of the Martian soil in that first meter is made of ice. This isn't just a little frost. Giant tongue-shaped formations seen in photographs of Mars now take on new significance: perhaps they are creeping, rock- covered glaciers. If so, Mars ice may be as thick as a kilometer in some places, which implies that there's a whole lot more water than even Odyssey is seeing. Glaciers would mean that Mars's past was warmer and wetter. Not Bermuda-shorts warm--more like the pleasanter parts of Antarctica, near the oceans, where every once in a while a snowstorm comes along.

Could life have gotten a start in such a bleak place? "The real question is, how long were the oceans there?" says Michael Meyer, a NASA exobiologist who ponders the possibility of extraterrestrial life in the solar system. On Earth it took 400 million years or so after the appearance of water for organic chemicals to jump-start themselves into a rudimentary form of life. Geologists, however, don't think Martian oceans were stable enough to hang around for that long. Photographs of Oceanus Borealis, a huge basin in the middle of the northeastern plains and former site of one of Mars's bigger oceans, reveal no evidence of a permanent shore. "This ocean was probably temporary," says Vic Baker, a planetary geologist at the University of Arizona. "It might have lasted a thousand years." Long enough to make glaciers, but not life.

But what about underground oceans (or at least ponds)? Some geologists believe that Mars harbors vast reservoirs of water deep down in its mantle--its hot, liquid interior. In the past, much of this water ...