smallest moon

The smallest moon with dimensions that are accurately known is Mars's satellite Deimos. Deimos is roughly ellipsoidal, measuring 15 by 12 by 11 km. A possible contender among other known objects is Jupiter's moon Leda, with an estimated diameter of order 10 km. It is difficult to determine with any accuracy the sizes of the small moons orbiting the outer planets since most have been seen only as point-like images. The size estimate depends on the value adopted for the moon's ability to reflect sunlight. Deimos, and Mars's other small moon, Phobos, are both believed to be captured asteroids. They are both very dark and reflect only a few percent of the light falling on them. They are similar to asteroids commonly found in the outer part of the asteroid belt and among Jupiter's Trojan asteroids. Leda is probably also an asteroid captured into orbit around Jupiter.