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.

Written by: Colin Dundas (narration: Tre Gibbs)  (18 October 2022)