A
minor-planet moon is an
astronomical object that
orbits a
minor planet as its
natural satellite. It is thought that many
asteroids and
Kuiper belt objects may possess moons, in some cases quite substantial in size. Discoveries of minor-planet moons (and binary objects, in general) are important because the determination of their orbits provides estimates on the
mass and
density of the primary, allowing insights of their physical properties that is generally not otherwise possible. As of December 2015, there are over 290 minor planets known to have moons.