Orbiter Images Suggest Water Flowed Recently on Mars

The photographs, from the Mars Global Surveyor orbiting the planet, show the same gullies in a crater taken in 1999 without the deposits, and again in 2005 with the moved sediment.

NASA scientists called the images the strongest evidence to date that Mars still has water occasionally flow on surface.

"The shapes of these deposits are what you would expect to see if the material were carried by flowing water," said Michael Malin of Malin Space Science Systems in San Diego, who is the principal investigator for the camera. "They have finger-like branches at the downhill end and easily diverted around small obstacles."

Water doesn't last long on Mars' surface since the atmosphere is so thin and the temperature so cold that liquid water would quickly evaporate or freeze, according to NASA.

Scientists already are aware of water ice and water vapor on the planet, but liquid water is necessary for life.

And although the Mars Exploration Rovers earlier discovered evidence that large swaths of the planet had pools of water millions of years ago, the new images raise the prospect that the planet is currently hospitable to life.

"This underscores the importance of searching for life on Mars, either present or past," said Bruce Jakosky, an astrobiologist at the University of Colorado at Boulder, who did not take part in the study, reported the Associated Press.

However, some scientists were skeptical that liquid water caused the surface features, when sand or dust can move like a liquid even without its presence.

"Nothing in the images, no matter how cool they are, proves that the flows were wet, or that they were anything more exciting than avalanches of sand and dust," Allan Treiman, a geologist at the Lunar and Planetary Institute in Houston told the AP.

The findings will appear in Friday's Science magazine.