NASA's Mars Global Surveyor shows a cluster of old, small impact craters on Mars. The group of craters was probably formed by secondary impacts following a much larger impact that occurred some distance away.

MGS MOC Release No. MOC2-431, 24 July 2003

This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a cluster of old, small impact craters near 36.3°N, 281.9°W. The group of craters was probably formed by secondary impacts following a much larger impact that occurred some distance away; the material that created these craters would have been the ejecta from the larger crater, rather than meteoroids from outer space. The craters cluster is considered to be relatively old because none of the craters have ejecta blankets any more, and each was filled, or partially filled, with layered material that was later eroded to form the terraced mounds found in their floors. This picture is illuminated from the lower left.

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