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Wednesday, February 27, 2008

Liquid Water Found Flowing on Mars? Not Yet

Liquid water has not been found on the Martian surface within the last decade after all, according to new research.

The finding casts doubt on the 2006 report that the bright spots in some Martian gullies indicate that liquid water flowed down those gullies sometime since 1999.

"It rules out pure liquid water," says lead author Jon Pelletier of The University of Arizona in Tucson.

Pelletier and his colleagues used topographic data derived from images of Mars from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. Since 2006, HiRISE has been providing the most detailed images of Mars ever taken from orbit.

The researchers applied the basic physics of how fluid flows under Martian conditions to determine how a flow of pure liquid water would look on the HiRISE images versus how an avalanche of dry granular debris such as sand and gravel would look.

"The dry granular case was the winner," says Pelletier, a UA associate professor of geosciences. "I was surprised. I started off thinking we were going to prove it's liquid water."

Finding liquid water on the surface of Mars would indicate the best places to look for current life on Mars, says co-author Alfred McEwen, a UA professor of planetary sciences.

"What we'd hoped to do was rule out the dry flow model -- but that didn't happen," says McEwen, the HiRISE principal investigator and director of UA's Planetary Image Research Laboratory.

An avalanche of dry debris is a much better match for their calculations and also what their computer model predicts, said Pelletier and McEwen.

Pelletier says, "Right now the balance of evidence suggests that the dry granular case is the most probable."

They added that their research does not rule out the possibility that the images show flows of very thick mud containing about 50 percent to 60 percent sediment. Such mud would have a consistency similar to molasses or hot lava. From orbit, the resulting deposit would look similar to that from a dry avalanche.

The team's research article, "Recent bright gully deposits on Mars: wet or dry flow?" is being published in the March issue of Geology.

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