NASA on 18 April 2017 said that its Mars Reconnaissance Orbiter (MRO) has captured a region of Mars sprayed with strange-shaped secondary craters.
In a statement, NASA said that the new images show the region of the red planet with secondary carters from 10-kilometer Zunil Crater to the north-west. The secondary craters are formed from the rocks that were ejected at high speed from the primary crater, which then impacts the ground at sufficiently high speed to make huge numbers of much smaller craters over a large region.
In the new images, however, the secondary crater ejecta have an unusual raised-relief appearance like bas-relief sculpture.
How did that happen?
One idea is that the region was covered with a layer of fine-grained materials like dust or pyroclastics about 1 to 2 meters thick when the Zunil impact occurred about a million years ago. The ejecta served to harden or otherwise protect the fine-grained layer from later erosion by the wind.