Mysterious Crater Deposits
HiRISE images often raise more questions than answers. For example, this image of the northern plains of Arabia Terra shows craters that contain curious deposits with mysterious shapes and distribution.
The deposits are found only in craters larger than 600 meters in diameter and are absent from craters measuring 450 meters and less. The deposits are located on the south sides of the craters but not in the north (although the cutout shows a crater that also has windblown deposits in the north). The deposits have horizontal laminations that could be layers or terraces. The deposits also have radial striations formed by small bright ridges.
We suspect that these features formed by sublimation of ice-rich material. The terraces might represent different epochs of sublimation. Perhaps the larger craters penetrated to a water table between 45 and 60 meters below the surface and were flooded after formation.
The map is projected here at a scale of 50 centimeters (19.7 inches) per pixel. (The original image scale is 59.3 centimeters [23.3 inches] per pixel [with 2 x 2 binning]; objects on the order of 178 centimeters [70.1 inches] across are resolved.) North is up.
The University of Arizona, in Tucson, operates HiRISE, which was built by Ball Aerospace & Technologies Corp., in Boulder, Colorado. 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.