HiRISE captured these enhanced-color images of Deimos, the smaller of the two moons of Mars, on 21 February 2009. Deimos has a smooth surface due to a blanket of fragmental rock or regolith, except for the most recent impact craters.
It is a dark, reddish object, very similar to Phobos, shown here in enhanced HiRISE colors (near-infrared, red, and blue-green). HiRISE took images of Phobos on 23 March 2008.
There are subtle color variations--redder in the smoothest areas and less red near fresh impact craters and over ridges or topographic highs (relative to its center of gravity). These color variations are probably caused by the exposure of surface materials to the space environment, which leads to darkening and reddening. Brighter and less-red surface materials have seen less exposure to space due to recent impacts or downslope movement of regolith.
With an image scale of about 20 meters/pixel, features 60 m or larger can be discerned. The images were acquired 5 hrs 35 minutes apart, so the sun was to the upper left in the first (left) image and to the right in the second image. Although the viewing geometry is similar in the two images, surface features appear very different due to the changes in illumination.