Lunar Photos Cast Doubt on Recent Mars Water, Astronomers Say

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Instead, he argues, the same formations could have been caused by flows of sand or dust. Such features aren't common on Earth because our planet is too wet for that much dust to accumulate.

But we do see something similar with avalanches of dry, powdery snow.

"Gwen took my idea and looked in a place where there isn't any water ever," he said.

Both Bart and Treiman point out that the lunar features do not prove that water didn't play a role in the Martian alcoves.

Rather, Bart said, their existence merely shows that there is a way to form such features in waterless environments.

A detailed comparison of lunar and Martian gullies will probably have to await better photos.

The moon images Bart used were taken prior to the first lunar landing in 1969. The shots are the best photos currently available of the moon's surface, but they are not as high-resolution as the orbital photos of Mars. (See a gallery of Mars images.)

Also, Dawes crater is old enough that its contours have been blurred by years of bombardment by dust-sized micrometeorites. That, too, makes it difficult to see details.

Even if details are visible, nobody currently knows what to look for. It's possible, Bart says, that there may be subtle differences between dry landslides and those triggered by water.

Jennifer Heldmann at the SETI Institute and NASA Ames Research Center believes she can see such differences in the existing images.

The Martian gullies, she said via email, look as though they were created by water, because they are sinuous, V-shaped, and cut into the underlying rock.

The gullies on the moon lack these features. Therefore she is "extremely skeptical" that they represent the same thing.

Still, the find is important because there is talk of visiting the Martian gullies in a future landing in the hopes of finding water and possible traces of life.

"In my view, that would be really chancy," Treiman, of the Lunar and Planetary Institute, said. "It might be that all you'd see would be dust."

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