for National Geographic News
Six years ago scientists studying images obtained by the Mars Orbital Cameraa probe that has been circling the red planet since 1997saw strange alcoves and gullies that looked like they had been created by liquid water.
The Martian features looked fresh enough that their discoverers, Michael Malin and Kenneth Edgett of Malin Space Science Systems in San Diego, California, concluded that they might have been formed as recently as a million years ago.
But now a Ph.D. student at the University of Arizona's Lunar and Planetary Laboratory has found similar features on the moon, which never had water.
Gwendolyn Bart was reexamining photos taken from lunar orbit in 1969 in an effort to better understand how rocks had been ejected from the moon's craters.
But she kept her eyes open for oddities, and one of the things she found was evidence of gullies that look strikingly similar to the Martian formations.
She spied the gullies in an image of a 10-mile-diameter (17-kilometer-diameter) crater called Dawes.
The lunar gullies' existence throws a potential wet blanket on the theory that Mars supported liquid water in the recent geologic past.
Bart presented her findings on March 16 at a gathering of lunar and planetary scientists in Houston, Texas. She said at the meeting that she believes the lunar gullies were formed by rockslides that were set off when the moon's surface was pelted by meteorites.
"Obviously they weren't formed by water," she told National Geographic News. "There's no evidence for water having been on the moon."
Bart's hunt for lunar rockslides was inspired by the work of Allan Treiman of the Lunar and Planetary Institute in Houston, who has long doubted that water was needed to form the Martian gullies.
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