Bumpy, Expanded Craters

Expanded craters on Mars are thought to occur when the upper slopes of an impact crater in an ice-rich target sublimate (going directly from a solid to a gaseous state). The vaporizing ice makes the walls retreat while the lower slopes are armored by dust and debris, resulting in a funnel-shaped formation.

The expanded craters in this image have an unusually bumpy texture in the outer apron where the sublimation occurred. The bumps are too large to be boulders. This suggests that the ice had concentrations of other material.

The map is projected here at a scale of 50 centimeters (19.7 inches) per pixel. (The original image scale is 59.6 centimeters [23.5 inches] per pixel [with 2 x 2 binning]; objects on the order of 179 centimeters [70.5 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.