Asteroid moon

An asteroid moon is an asteroid that orbits another asteroid. Dactyl is an asteroid moon which orbits 243 Ida. It is thought that many asteroids may possess moons, in some cases quite substantial in size. Asteroids whose moon is roughly the same size as the asteroid itself may be referred to as binary asteroids.

The origin of asteroid moons is not currently known with certainty, and a variety of possibilities exist. A widely accepted theory is that asteroid moons are formed from debris knocked off of the primary asteroid by an impact.