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The New York Times
December 6, 2006
Mars Spacecraft Finds Evidence of Water
By WARREN E. LEARY
WASHINGTON, Dec. 6 — Pictures of Martian gullies taken years apart strongly suggest that liquid water still flows on the surface of the planet, scientists announced on Wednesday.
The photographs by NASA’s Mars Global Surveyor spacecraft, which fell silent last month after almost 10 years of observing the planet from orbit, show what appear to be light-colored deposits in two gullies on crater walls. They were not present in earlier photographs.
The deposits appear to be materials left by water that percolated to the surface and flowed down the gullies, said Michael Malin, chief scientist for the spacecraft’s camera system. The water would have quickly evaporated on the planet’s surface because of low atmospheric pressure and temperatures, he added.
“The shapes of these deposits are what you would expect to see if the material were carried by flowing water,” Mr. Malin said during a televised news conference held here at NASA headquarters. The deposits appeared to have been left by a liquid mixed with dirt or other material that flowed down a slope for hundreds of yards, he said.
“We think water was the fluidizing material here,” said Mr. Malin, president of Malin Space Science Systems of San Diego, Calif.
Water in the forms of ice and vapor are known to exist on Mars, and spacecraft have found evidence that liquid water was once present on the planet’s surface. Some scientists believe that water might still exist in liquid form under the planet’s surface, which, if the case, raises the possibility of microbial life on Mars.
“These observations give the strongest evidence to date that water still flows occasionally on the surface of Mars,” said Michael Meyer, lead scientist for NASA’s Mars Exploration Program.
Kenneth Edgett, another scientist with Malin Space Science Systems, said that whenever the surface of Mars is disturbed — by asteroids, for instance, or NASA’s mechanized ground rover — it takes on a dark complexion. The light tone of the material in the flow patterns suggest minerals or other chemicals that were in the water, he said.
“The bright features persist for several years,” Mr. Edgett said, “which means it’s not likely to be frost and is likely to be sediment from water flow.”
In a paper to be published Thursday in the journal Science, the researchers said comparing pictures taken in 2004 and 2005 of the same areas clearly show changes since images were first photographed in 1999. Some scientists have suggested that past flow patterns seen in craters might have been caused by landslides or rock falls. But the geological properties of these craters strongly suggest that the changes were caused by a fluid, likely water, the researchers said.
Philip Christensen, a professor of geological science at Arizona State University, said he has been skeptical of previous claims about signs of flowing water, but found the new evidence “reasonable and plausible.”
“I’m about 80 percent convinced that this is evidence of water flow happening now and I admit I have been a skeptic,” he said in an interview.
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http://www.nytimes.com/2006/12/06/science/07marscnd.html?hp&ex=1165467600&en=f7a408f3b452a005&ei=5094&partner=homepage
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