Dry Debris, Not Water, Caused Recent Flows on Mars

  A dry landslide—not liquid water—is the most likely explanation for at least one of the bright streaks seen recently on Mars, a new study concludes. The streaks first made waves in 2006, when scientists reported them in pictures of Martian gullies taken in 2005. Mars Close-Up Casts Doubts on Signs of Recent Water (September 20, 2007) Lunar Photos Cast Doubt on Recent Mars Water, Astronomers Say (March 21, 2006) Pictures: Exploring Mars The features had not been in images of the same region from 1999, indicating that something had flowed down those gullies recently. At the time the researchers figured the most likely candidate was a flash flood—which would have offered proof of liquid water on modern Mars. The new paper, published this month in the journal Geology, concludes that the shape of at least one of the bright deposits doesn't match the way water would flow. This doesn't mean that Mars never had water, but it does cast doubt on more recent liquid flowing on the red planet. The study team, led by Jon Pelletier of the University of Arizona, examined topographic maps made using high-resolution 3-D imagery from the HiRISE Mars-orbiting camera. (See some of the first color images of Mars released last year by the HiRISE team.) The new maps not only provided a more detailed look at the features, they allowed the team to model the flows based on the steepness of the slopes. "If we know where the flow originated and know the slope angle, we can mathematically model how [material] ran down the slope," Pelletier said. "We tried to get both the extent of the runout and also match the shape of the flow," he said. "We were actually trying to strengthen the case for [water]."

Telltale Fingers

But the team instead found that the shape of the deposit just didn't match with a liquid flash flood.