A Crater in Scalloped Terrain

Sublimation (ice vaporizing without passing through a liquid stage) is an important process affecting water ice in the mid-latitudes of Mars. This might be responsible for creating two different landforms: scalloped depressions and expanded craters.

Scalloped depressions are oval or irregular pits with relatively steep pole-facing slopes, and expanded craters appear to be impact craters that have grown larger as the upper slopes sublimate, while dust and debris protect the bottom.

The two usually do not occur together, but here we see what appears to be a slightly expanded crater in a field of scalloped depressions. It's possible that it will evolve over time to look more like the scallops. Unfortunately, this process is too slow to see with before-and-after HiRISE images, even if they were spaced years apart.

The map is projected here at a scale of 25 centimeters (9.8 inches) per pixel. (The original image scale is 25.1 centimeters [9.9 inches] per pixel [with 1 x 1 binning]; objects on the order of 50.3 centimeters [19.8 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.