Mars' Ice Patchy, Water Cycle Quite Active, Study Reveals

Odyssey's Thermal Emission Imaging System uses an infrared system to see details as small as 330 feet in width, which is much better than the accuracy of previous images that spanned several hundreds of miles. Some of these new and improved images of Mars were targeted at locations where subsurface water has been found. In doing this, surface temperature changes during Mars' seasons were made visible, revealing just how deep the ice layers were in those areas. Patchy patterns in the ice seem to behave much like those of Earth (fine grained material insulates the ice, allowing it to get close to the surface, whereas a rockier surface will transfer heat beneath it, melting the ice). The Odyssey's thermal imaging shows that Mars on a larger scale may have gone through multiple climate changes, as Earth does. This means that Mars' water cycle may actually still be "active."

http://news.nationalgeographic.com/news/2007/05/070502-mars-ice.html