Evidence Shows Water Flows on Mars

By Rick Weiss
Washington Post Staff Writer
Wednesday, December 6, 2006; 7:26 PM

Photographs of the Martian surface taken by an orbiting spacecraft have revealed powerful evidence that liquid water occasionally flows on the Red Planet's surface, an unexpected finding that suddenly increases the odds that the planet may harbor some kind of life.

Scientists have long known that water exists on Mars as polar ice and atmospheric vapor. But a core requirement for life is water in liquid form, a commodity that has been seemingly absent on that cold and ruddy planet.

Thousands of dry gullies scar the face of Mars, indicating that surface water once flowed there. But until now it has been impossible to tell whether those gullies last saw water millions of years ago or much more recently -- periodically fed, perhaps, by aquifers that might persist underground to this day.

Now a comparison of photographs taken several years apart by NASA's Mars Global Surveyor has found that two gullies, at least, experienced flash floods in between photo shoots.

"Water seems to have flowed on the surface of today's Mars," said Michael Meyer, lead scientist for NASA's Mars Exploration Program, speaking at a news conference today . "The big question is how does it happen, and does it point to a habitat for life?"

The global surveyor went into orbit around Mars in the fall of 1997 and, during its longer-than-expected nine-year life, mapped the planet's surface with more than 240,000 images before going dark last month.

In 2000, scientists from Malin Space Science Systems in San Diego, which developed and operated the camera equipment on the surveyor, reported the discovery of many gullies that they said had clearly been carved by water. The timing of that erosion remained up for grabs until two of them -- photographed in 1999 and 2001 -- were re-shot in 2004 and 2005.

As described at today's event and in an article appearing in Friday's issue of the journal Science, both looked radically different on the second pass than they did earlier . Most noticeable, each has a fresh coat of fine, pale sediment, which scientists say appears to be either water frost or salts left behind by briny water.

Flow patterns around rocks or other obstacles, clearly visible in those sediments, are exactly as would be expected from viscous water -- a slush of water and sediment akin to a mud flow-- and are different than would be expected if wind or other forces had been at work, the researchers said. The gullies, each one about one-quarter of a mile long, also have new delta-like drainage fingers splaying from their bases.

Malin scientist Kenneth Edgett said the team had calculated that each flow probably involved about as much water as would fill five to ten swimming pools.

"If you were there . . . you'd probably want to get out of the way," Edgett said. All the more so, he said, because at the low atmospheric pressures found on Mars, much of that water would be bubbling and boiling -- even though it would not be hot.

"It would be like, 'Wow, there's this thing coming at me!' " Edgett said.


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