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Don’t panic – its only Deimos. But what an image this is of the smaller moon of Mars! HiRISE captured this enhanced-color image of Deimos on February 21, 2009, showing the moon’s smooth surface – with a few impact craters here and there. The one crater near the middle that looks sharp and crisp was created relatively recently. Deimos is composed fragmental rock, or regolith, rich in carbonaceous material, much like C-type asteroids and carbonaceous chondrite meteorites. Deimos is noticeably smoother than Phobos. (See images of Phobos taken by HiRISE in 2008). HiRISE took two images of Deimos, about five and a half hours apart – see below.
These images have a scale of about 20 meters/pixel, so the features 60 meters or larger can be seen. 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.
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). The HiRISE scientists say 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.
Deimos is named after a figure in Greek mythology representing panic or dread. Only two geological features on Deimos have been given names: the craters Swift and Voltaire are named after two writers who speculated on the existence of Martian moons before they were discovered.