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Southern spring on Mars brings sublimation of the seasonal dry ice polar cap. Gas trapped under the seasonal ice sheet carves channels on its way to escaping to the atmosphere.

At this site, the channels are wider than we see elsewhere on Mars, perhaps meaning that the spider-like (or more scientifically, "araneiform"�) terrain here is older, or that the surface is more easily eroded. Seasonal fans of eroded surface material, pointed in two different directions, are deposited on the remaining ice.

The University of Arizona, Tucson, operates HiRISE, which was built by Ball Aerospace & Technologies Corp., Boulder, Colo. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the Mars Reconnaissance Orbiter Project for NASA's Science Mission Directorate, Washington.