This image shows many small craters over a larger degraded one in the northern lowlands. These small craters are smoother and shallower than their counterparts closer to the equator.

Scientists believe this difference is a result of impact into a region with subsurface ice, which sublimates when exposed to the Martian atmosphere. This causes the crater to gradually expand and flatten after impact.

Written by: HiRISE Targeting Specialists (audio: Tre Gibbs)   (24 August 2016)

More info and image formats at http://hirise.lpl.arizona.edu/ESP_044037_2345

Image: NASA/JPL/University of Arizona