Gwendolyn D. Bart of the University of Arizona in Tucson said she thinks it might be premature to conclude that certain recent Martian gullies – made within the last million years on the sides of some craters – were carved by water.

Her assertion counters hypotheses by scientists interpreting images from the Mars Orbital Camera taken five years ago. Writing in an issue of the journal Science, the scientists concluded from the images that liquid water flowed on the Martian surface relatively recently.

Bart told attendees at the 37th Lunar and Planetary Science Conference that craters on the Moon also have gullies that look exactly like their counterparts on Mars – which means some other process could produce such features.

"We'd all like to find liquid water on Mars," Bart said. "That would be really, really exciting. If there were liquid water on Mars, humans wouldn't have to ship water from Earth when they go to explore the planet. That would be an enormous cost savings. And liquid water near the surface of Mars would greatly increase the chances for native life on Mars."

She said she heard a presentation last year by Allan Treiman of the Lunar and Planetary Institute, in which he suggested the Martian gullies might be dry landslides possibly instigated by the intense planetary wind.

Bart said she recently studied high-resolution images of the Lunar landscape taken in 1969, prior to the Apollo landings. "Totally by accident, I saw gullies that looked strikingly like the gullies on Mars," she explained. "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 - we do."

She said Gullies in the moon's 10-mile-diameter (17 kilometer) crater Dawes are similar in structure and size to those in a Martian crater the MOC photographed. Micrometeorites hitting the smooth slopes and crater on the airless moon easily could trigger small avalanches that form gullies, Bart added.

The Martian gullies also resemble gullies on Earth that were formed by water, she noted. "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."

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