From: Reuters
Published February 29, 2008 04:34 PM

Study casts doubt on water on Mars surface

By Will Dunham

WASHINGTON (Reuters) - It made a big splash when scientists announced in 2006 that images from a NASA spacecraft indicated water apparently had flowed on the surface of Mars in the past decade but new research casts doubt on that finding.

Other scientists on Friday said new images and computer simulations strongly indicate that a landslide of sand and gravel is a more likely explanation for the bright deposits in gullies previously touted as evidence of recent water flow.

"We started off not thinking that we were going to debunk anything. I absolutely thought it was going to be liquid," Jon Pelletier, a professor of geosciences at the University of Arizona who led the new study, said in a telephone interview.

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Using previous images from NASA's Mars Global Surveyor and newer, higher-resolution readings from NASA's Mars Reconnaissance Orbiter, the team created three-dimensional pictures of one of the geological formations showing downhill flow in a crater.

The scientists then ran computer simulations of what conditions might have caused such a formation. Flows of liquid water did not really match the formation in the computer models but flows of dry, granular material like sand and gravel matched it almost perfectly, they reported in the journal Geology.

"What we'd hoped to do was rule out the dry flow model -- but that didn't happen," University of Arizona planetary sciences professor Alfred McEwen said in a statement.

Pelletier said his research cannot absolutely rule out that liquid water created the flow formation, measuring about 1,600 feet long and up to 330 feet wide.

Another possibility is that flows of thick mud containing about 50 percent to 60 percent sediment with a consistency similar to molasses or lava might be responsible.

"The simplest explanation is that it is dry, granular flow," Pelletier said. "We think that the simpler explanation is probably the correct one."

The presence of water on Mars is a hot topic for scientists. They have presented strong evidence of huge deposits of frozen water at the Martian poles and point to geological features that indicate that large bodies of water have flowed on the planet's surface in the distant past.

Water is a key to the question of whether life, even in the form of mere microbes, ever existed on Mars. On Earth, all forms of life require water to survive.

Kenneth Edgett of Malin Space Science Systems in San Diego, who was involved in the 2006 study suggesting the flows were liquid, declined comment.

(Editing by Maggie Fox and Bill Trott)

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