Phobos
Phobos is the larger of Mars' two moons, although it is still very tiny, being only about seventeen miles in diameter. You can see in the picture at right that Phobos has a an impact crater on one end that is very large relative to the size of the moon. The impact crater has striations, or streaks, spreading out from it that indicate that whatever struck the tiny moon did so with such force that it almost broke the moon into many pieces.

Deimos
Even though Deimos has many, many impact craters as a result of being struck by thousands of smaller objects during its long life, most of these craters have been filled by a layer of dust that covers the small moon. Like its companion moon, Deimos is slowly being drawn closer to the surface of Mars and will eventually impact in the surface of the red planet.