|ALL ABOUT MARS|
Deimos is the smaller of the two Martian moons and is less irregular in shape. The largest crater on Deimos is approximately 2.3 km in diameter, 1/5 the size of the largest crater on Phobos. Although both moons are heavily cratered, Deimos has a smoother appearance caused by the partial filling of some of its craters. When impacted, dust and debris will leave the surface of the moon because it doesn't have enough gravitational pull to retain the ejecta. However, the gravity from Mars will keep a ring of this debris around the planet in approximately the same region that the moon orbits. As the moon revolves, the debris is redeposited as a dusty layer on its surface.