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Minor-planet moon
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 October 2015, there are over 270 minor planets known to have moons.〔
== Terminology ==
In addition to the terms ''satellite'' and ''moon'', the term "binary" (binary minor planet) is sometimes used for minor planets with moons, and "triple" for minor planets with two moons. If one object is much bigger it can be referred to as the ''primary'' and its companion as ''secondary''. The term ''double asteroid'' is sometimes used for systems in which the asteroid and its moon are roughly the same size, while ''binary'' tends to be used independently from the relative sizes of the components. When binary minor planets are similar in size, the Minor Planet Center (MPC) refers to them as "binary companions" instead of referring to the smaller body as a satellite. A good example of a true binary is the 90 Antiope system, identified in August 2000. Small satellites are often referred to as moonlets.〔 (mentions both 90 Antiope and 762 Pulcova)〕〔(【引用サイトリンク】title=IAUC 8732: S/2006 (624) 1 ) (Satellite Discovery)〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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