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.