"Mars seems to have quite a bit of snow," said Philip Christensen, principal investigator for the Mars Odyssey's thermal emission imaging system at Arizona State University. "The young gullies of Mars were caused by melting of extensive snowpacks."

In June 2000, the probe Mars Global Surveyor took remarkable photographs of ravines and gullies on the surface of Mars while orbiting the planet.

At that time, researchers said the ravines could have been created by mud flows triggered by underground water.

"The problem is that liquid water coming out of the ground will very rapidly freeze or evaporate, making very hard to explain how those gullies could be formed," said Christensen, who heads a team of researchers working on the thermal emission imagery system Themis for another National Aeronautics and Space Administration probe, the Mars Odyssey.

By combining the images from the Mars Global Surveyor and Mars Odyssey, Christensen has developed a new theory, which claims that certain slow evaporation geological deposits observable on the surface of Mars are actually snowpacks covered with a fine layer of dust.

They are "remnants of a once very extensive layer of snow that covers the mid-latitude of Mars," argued the researcher. "This snow draped the landscape. As the climate warmed, the snow melted. That melt water trickled through the snow and actually eroded the gullies."

The study is published in the online edition of the review Nature.

SPACE.WIRE