At first glance this scene may seem nothing out of the ordinary, but the large elongated crater marks the imprint of an impacting body that may have broken into three before it hit Mars. The images were acquired by ESA’s Mars Express on 28 January, and focus on one of the oldest regions on Mars, Terra Sirenum, in the southern highlands.
The elongated trough at centre stage in this scene is 45 km long and 24 km across. Inspection of the outline suggests that two similarly sized craters and one smaller one have merged to create the footprint-like shape.
Two groups of raised material can be seen in the crater floor. These peaks are created as the initial crater cavity produced by the impact collapses under gravity. The smaller crater also has a hint of a central peak.
Craters like these are thought to have formed at the same time, but there are a number of ideas as to how it happened. For example, an object could have broken into smaller pieces after it entered the atmosphere, striking the surface in quick succession in the same place…. [More at link]