Martian Waterworks

Time was when the solar system had two watery worlds. Directly next door to the warm, wet, loamy Earth was the warm, wet, loamy Mars, both planets sloshing with oceans and running with rivers--and both possibly teeming with life. Billions of years ago, however, the low-gravity Mars had both its air and water leak away, causing the planet to become the dead, freeze-dried place it is today.

That, in any case, is what the prevailing thinking has been. Now, however, it appears that thinking may be wrong. Last week NASA released a flurry of new images from the Mars Global Surveyor spacecraft that suggest that even today, water may be flowing up from the Martian innards and streaming onto the Martian surface--dramatically increasing the likelihood that at least part of the planet is biologically alive. "If these results prove true," says Ed Weiler, associate administrator of NASA's Office of Space Science, "[they have] profound implications for the possibility of life."

Finding liquid water on Mars' surface has never been easy--mostly because it simply can't exist there. The modern-day Martian atmosphere has barely 1% the density of Earth's, and the planet's average temperature hovers around a paralyzing -67[degrees]F. In an environment as harsh as this, any water that did appear would either vaporize into space or simply flash-freeze where it stood. What scientists studying Martian history have always looked for instead are clues that the planet's ancient water left behind--tracks where vanished rivers once flowed, basins where vanished seas once stood.

The 65,000 or so images the Surveyor orbiter has beamed home in the nearly three years it has been circling Mars are full of this kind of expected hydro-scarring. But a handful of the pictures took scientists by surprise. In general, the older a Martian formation is, the more likely it is to have been distorted over the eons--smoothed by the planet's periodic windstorms or gouged by the occasional incoming meteor. A few of the newly discovered water channels, however, look as fresh as the day they were formed, leading astonished researchers to conclude that that day may have been remarkably close to the present one. Says Weiler: "The water could have flowed perhaps a million years ago, perhaps 10,000 [years ago], perhaps yesterday."

If the pristine nature of the formations was unexpected, their unlikely location was even more so. Planetologists have long assumed that if underground water was going to bubble up on Mars, it would have to be somewhere in the comparatively balmy equatorial zones, where temperatures at high noon in midsummer may approach a shirtsleeves 68[degrees]F. Almost all the new channels, however, were spotted at the planet's relative extremes--north of 30[degrees] north latitude and south of 30[degrees] south--and all were carved on the cold, shaded sides of slopes.