Posted: Fri, Sep 21, 2007, 8:15 AM ET (1215 GMT)
Data from NASA's Mars Reconnaissance Orbiter (MRO) suggest that gullies that recently formed in some Martian craters were not created by liquid water. The gullies had formed in crater walls some time between two sets of Mars Global Surveyor images taken several years part, and scientists speculated that groundwater leaking out the side of the crater could have caused the gullies. However, more detailed observations by MRO argue that the gullies were formed by landslides of loose, dry material. Other MRO observations of much older features may be evidence that any liquid water that existed on the planet's surface early in its history was short-lived.

Related Links:

•  New Scientist article
•  SPACE.com article
•  Scientific American article
•  NASA press release