Warrego Valles on Mars (IMAGE) Brown University Caption Valley networks on Mars are a good sign that water once flowed on the surface. Researchers from Brown University have found that some of these valleys appear to have been formed by orographic precipitation -- rain or snow that falls when moist air is pushed upward by mountain ridges or raised crater rims. The findings suggest that at least some of the water on ancient Mars fell from the atmosphere, rather than bubbling up from the subsurface. The image, taken by the Mars Reconnaissance Orbiter, shows a valley network in a region called Warrego Valles. Credit NASA/JPL-Caltech/Univ. of Arizona Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.