Gullies on Mars Not Formed by Water?

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SUMMARY: Gullies on Mars were discovered in 2001 that seemed to show evidence that liquid water had been on the surface of the planet very recently. But a theory from a University of Melbourne geologist examines the possibility that the gullies were carved by an avalanche of carbon dioxide changing directly from a solid to a gas. This theory has been met with skepticism from other Mars researchers, who are hoping that liquid water might someday be found on Mars, increasing the possibility of finding life.

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Also: from the LPSC, PhysOrg.com: Water May Not Have Formed Mars' Recent Gullies

Recently, Bart was studying the lunar landscape in high-resolution images taken in 1969, prior to the Apollo landings, for her research on processes that modify the lunar surface.

"Totally by accident, I saw gullies that looked strikingly like the gullies on Mars," she said.

"If the dry landslide hypothesis for the formation of martian gullies is correct, we might expect to see similar features on the moon, where there is no water," she said. "We do."
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"My point is that you can't just look at the Mars gullies and assume they were formed by water. It may be, or may be not. We need another test to know."