Mars has two moons. Phobos is just 22 kilometers wide, and Deimos is 13. They may be captured asteroids, but that would make their nice, circular orbits hard to explain, so we're not sure. Phobos has a huge crater, and lots of odd, parallel streaks. The color and brightness were greatly enhanced in this image. This
is what it really looks like.
Credit: NASA/JPL/University of Arizona