Minor planet

A minor planet is an astronomical object in direct orbit around the Sun (or more broadly, any star with a planetary system) that is exclusively classified as neither a planet nor a comet.[lower-alpha 1] Before 2006, the International Astronomical Union (IAU) officially used the term minor planet, but that year's meeting reclassified minor planets and comets into dwarf planets and small Solar System bodies (SSSBs).[1]

Euler diagram showing the types of bodies in the Solar System

Minor planets include asteroids (near-Earth objects, Mars-crossers, main-belt asteroids and Jupiter trojans), as well as distant minor planets (centaurs and trans-Neptunian objects), most of which reside in the Kuiper belt and the scattered disc. As of May 2022, there are 1,131,201 known objects, divided into 611,678 numbered (secured discoveries) and 519,523 unnumbered minor planets, with only five of those officially recognized as a dwarf planet.[2]

The first minor planet to be discovered was Ceres in 1801. The term minor planet has been used since the 19th century to describe these objects.[3] The term planetoid has also been used, especially for larger, planetary objects such as those the IAU has called dwarf planets since 2006.[4][5] Historically, the terms asteroid, minor planet, and planetoid have been more or less synonymous.[4][6] This terminology has become more complicated by the discovery of numerous minor planets beyond the orbit of Jupiter, especially trans-Neptunian objects that are generally not considered asteroids.[6] A minor planet seen releasing gas may be dually classified as a comet.

Objects are called dwarf planets if their own gravity is sufficient to achieve hydrostatic equilibrium and form an ellipsoidal shape. All other minor planets and comets are called small Solar System bodies.[1] The IAU stated that the term minor planet may still be used, but the term small Solar System body will be preferred.[7] However, for purposes of numbering and naming, the traditional distinction between minor planet and comet is still used.


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