NASA has just found one of the key elements of life on the red planet: liquid water. New photos taken by the Mars Global Surveyor satellite show "bright new deposits" in two Martian gullies. NASA says the appearance of those deposits suggests water has carried sediment through the gullies some time during the past seven years. Water ice and water vapor have already been spotted on Mars, but according to NASA Mars Exploration Program Lead Scientist Michael Meyer, "These observations give the strongest evidence to date that water still flows occasionally on the surface of Mars."

The light tone of the deposits could be from surface frost continuously replenished by ice within the body of the deposit. Another possibility is a salty crust, which would be a sign of water's effects in concentrating the salts. If the deposits had resulted from dry dust slipping down the slope, they would likely be dark, based on the dark tones of dust freshly disturbed by rover tracks, dust devils and fresh craters on Mars.

Mars Global Surveyor has discovered tens of thousands of gullies on slopes inside craters and other depressions on Mars. Most gullies are at latitudes of 30 degrees or higher. Malin and his team first reported the discovery of the gullies in 2000. To look for changes that might indicate present-day flow of water, his camera team repeatedly imaged hundreds of the sites. One pair of images showed a gully that appeared after mid-2002. That site was on a sand dune, and the gully-cutting process was interpreted as a dry flow of sand.