Minor-planet moonA minor-planet moon is an astronomical object that orbits a minor planet as its natural satellite. As of September 2026, there are 638 minor planets 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 into their physical properties that are generally not otherwise accessible.
AsteroidAn asteroid is a minor planet—an object larger than a meteoroid (thus 1 meter or larger) that is neither a planet nor an identified comet—that orbits within the inner Solar System or is co-orbital with Jupiter (Trojan asteroids). Asteroids are rocky, metallic, or icy bodies with no atmosphere, and are broadly classified into C-type (carbonaceous), M-type (metallic), or S-type (silicaceous).
45 Eugenia45 Eugenia is a large asteroid of the asteroid belt. It is famed as one of the first asteroids to be found to have a moon orbiting it. It was also the second triple asteroid to be discovered, after 87 Sylvia. DiscoveryEugenia was discovered on 27 June 1857 by the Franco–German amateur astronomer Hermann Goldschmidt. His instrument of discovery was a four-inch aperture telescope located in his sixth-floor apartment in the 6th arrondissement of Paris.
22 Kalliope22 Kalliope (; ) is a large M-type asteroid from the asteroid belt discovered by J. R. Hind on 16 November 1852. It is named after Calliope, the GreekMuse of epic poetry. It is orbited by a small moon named Linus. CharacteristicsKalliope is somewhat elongated, approximately 166 km in diameter, and slightly asymmetric, as evidenced by resolved images taken with the VLT at the European Southern Observatory.
87 Sylvia87 Sylvia is one of the largest asteroids (approximately tied for 7th place, to within measurement uncertainties). It is the parent body of the Sylvia family and member of Cybele group located beyond the main asteroid belt (see minor-planet groups). Sylvia was the first asteroid known to possess more than one moon. Discovery and namingSylvia was discovered by N. R. Pogson on 16 May 1866, from Madras (Chennai), India.
130 Elektra130 Elektra is a large outer main-beltasteroid and quadruple system with three minor-planet moons. It was discovered on 17 February 1873 by astronomer Christian Peters at Litchfield Observatory, New York, and named after Electra, an avenger in Greek mythology. Description(130) Elektra has the spectrum of a G-type asteroid; hence it probably has a Ceres-like surface.
121 Hermione121 Hermione is a very large binary asteroid discovered in 1872. It orbits in the Cybele group in the far outer asteroid belt. As an asteroid of the dark C spectral type, it is probably composed of carbonaceous materials. In 2002, a small moon was found to be orbiting Hermione. DiscoveryHermione was discovered by J. C. Watson on 12 May 1872 from Ann Arbor, Michigan, in the United States, and named after Hermione, daughter of Menelaus and Helen in Greek mythology.
107 Camilla107 Camilla is one of the largest asteroids from the outermost edge of the asteroid belt, approximately 250 kilometers (160 miles) in diameter. It is a member of the Sylvia family and located within the Cybele group. It was discovered on 17 November 1868, by English astronomer Norman Pogson at Madras Observatory, India, and named after Camilla, Queen of the Volsci in Roman mythology.
243 Ida243 Ida is an asteroid in the Koronis family of the asteroid belt. It was discovered on 29 September 1884 by Austrian astronomer Johann Palisa at Vienna Observatory and named after a nymph from Greek mythology. Later telescopic observations categorized Ida as an S-type asteroid, the most numerous type in the inner asteroid belt. On 28 August 1993, Ida was visited by the uncrewed Galileo spacecraft while en route to Jupiter.
Galileo (spacecraft)Large Strategic Science MissionsPlanetary Science Division← Voyager 1Cassini–Huygens →Galileo was an American robotic space probe that studied the planet Jupiter and its moons, as well as the asteroids Gaspra and Ida. Named after the Italian astronomer Galileo Galilei, it consisted of an orbiter and an entry probe. It was delivered into Earth orbit on October 18, 1989, by Space ShuttleAtlantis, during STS-34.
Barycenter (astronomy)In astronomy, the barycenter (or barycentre; from Ancient Greek (barús)'heavy' and (kéntron)'center') is the center of mass around which two or more bodies orbit. A barycenter is a dynamical point, not a physical object. It is an important concept in fields such as astronomy and astrophysics. The distance from a body's center of mass to the barycenter can be calculated as a two-body problem.*As an Amazon Associate I earn from qualifying purchases.