Water-carved gullies on Mars

Carved into many Martian dunes are narrow, sinuous channels. Studies of their morphology and laboratory simulations suggest that the likely origin of the gullies is surface or near-surface water ice that melts and forms a flowing slurry of sandy debris. Dennis Reiss and colleagues at the University of Münster’s Institute for Planetology report new evidence for such transient liquid water. Their observations rely on data from the High Resolution Imaging Science Experiment, a camera on the Mars Reconnaissance Orbiter that provides nearly 10 times the resolution of the camera aboard the earlier Mars Global Surveyor. Armed with 23 sequential HiRISE images of the Russell crater dune field in Mars’s southern hemisphere over two successive Martian years (spanning November 2006-May 2009), the researchers uncovered signs of multiple flow events that, as seen in this image, deepen and widen the channels. They also observed gullies lengthening over the course of the early Martian spring. Factoring in near-IR reflectance data, which tracked the melting of frozen carbon dioxide, and calculations of daily springtime temperature profiles at the surface, they discount dry flows and CO₂ flow mechanisms; they instead conclude that the gully changes are best explained by the seasonal melting of small amounts of water ice. (D. Reiss et al., Geophys. Res. Lett. 37 , L06203, 2010 http://dx.doi.org/10.1029/2009GL042192 .)