A minor-planet moon is an astronomical object that orbits a minor planet as its natural satellite. As of June 2021, there are known or suspected to have moons. 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. There are also several known ring systems around distant objects (see: rings of Chariklo and Chiron).