This observation shows part of the floor of a large impact
crater in Arabia Terra. This crater formed in the distant past
when a large asteroid or comet struck Mars, and has been heavily
modified since formation. The crater was partially filled by
sediments, forming the rock outcrops and layers visible in this
image. After this material was laid down, part of the deposits
were eroded away. The central part of the image has been carved
especially deeply, forming a distinct depression. This
depression has been a site of aeolian (wind) transport of sand
in more recent times. A particularly interesting aspect of this
site is that there appears to have been multiple styles of
aeolian activity. Both large sand dunes (the dark hills, deep
blue in the color image) and smaller ripples (sharp, light-toned
narrow ridges) are visible. While ripples are often found in
association with dunes, the different colors suggest that the
material is not the same. (At full resolution, the surfaces of
both the dunes and the large ri