Mars Reconnaissance Orbiter images of channels and gullies cut in the sides and floor of this 7 mi. diameter crater on the northern plains of Mars are indicative of water erosion and subsurface ice at this location known as Acidalia Planitia. The Image from the HiRise high resolution imaging system has a 24 in. resolution, meaning boulders as small as 2 ft, diameter are visible along with linear features much smaller than that. Click image to enlarge.(Photo credit: JPL/University of Arizona)
The gullies and alcoves cut in the crater rim originate at the same height, suggesting that the carving agent -- most likely water -- emanated from one single layer exposed in the crater's wall.
The muted topography of the crater and its surroundings, the relatively shallow floor, the convex slope of its walls—all are consistent with water ice being present under the surface. Ice would have acted as a lubricant, facilitating the flow of rocks and soils and hence smoothing landscape's features such as ridges and crater’ rims. The concentric and radial fissures in the crater's floor may indicate decrease of volume due to loss of underground ice. Piles of rocks aligned along these fissures and arranged forming polygons are similar to features observed in Antarctica. Watch this space for continuing coverage of Mars.
-- Craig Covault
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