NASA's HiRISE camera captured this full view of Phobos on March 23, 2008. The 5.6-mile-wide (9-kilometer-wide) Stickney Crater sits in the lower right.

The impact that created Stickney is thought to have almost shattered the roughly 17-mile-wide (27-kilometer-wide) moon.

Phobos and the only other Martian moon, Deimos, are both about the same size and composition as asteroids, leading some astronomers to think the moons might be asteroids that were captured by Mars's gravity.

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