WASHINGTON, D.C.--Water has recently flowed from crater and valley walls on Mars and may be seeping still, planetary geologists announced Thursday morning at a press conference at NASA headquarters. Although the news followed a Web-fueled media torrent that spoke of towering geysers and gurgling springs, even the prospect of liquid water merely oozing to the martian surface is not trivial. "If these results prove true, that there is water near the surface of Mars," said NASA associate administrator Edward Weiler, "it has profound implications for the possibility of life on Mars."
The evidence comes from the high-resolution camera that has been orbiting Mars on Mars Global Surveyor the past 2 years. In about 200 of the 65,000 images returned so far, planetary geologists Michael Malin and Kenneth Edgett of Malin Space Science Systems Inc. in San Diego found places where water appears to have emerged from a crater wall or valley side. A preview of their report, which will appear in the 30 June issue of Science, is available. It looks as though chunks of the slope collapsed and flowed down to form a debris pile cut by channels. These "aproned alcoves" are so devoid of impact cratering and other ravages of time that they must be "very, very young," Edgett says. As Weiler put it, "they can't say it wasn't yesterday" that water was seeping out of the ground on Mars.
Malin and Edgett speculate that liquid water flowed through the shallow crust--where martian life could conceivably be lurking--and froze as it approached a crater wall. That ice dam then broke, releasing pent-up water and debris. No one contacted by Science doubts that a fluid emerging from the martian rock formed these stunningly Earth-like features. "The interpretation these are water-worn features is very compelling," said long-time Mars geologist Michael Carr of the U.S. Geological Survey in Menlo Park, California, who spoke at the press conference.
But Carr can't imagine what would keep water liquid, given the absence of any apparent sources of volcanic heat nearby. He can imagine an exotic and easily destabilized ice of carbon dioxide and water called clathrate blowing out gobs of gas and debris to form channeled aprons, but the whole thing "is troubling me," he says. "The important thing at this stage is to be cautious about the interpretation."