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According to the International Astronomical Union (IAU), a minor planet is an astronomical object in direct orbit around the Sun that is exclusively classified as neither a planet nor a comet.[a] Before 2006, the 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] In contrast to the eight official planets of the Solar System, all minor planets fail to clear their orbital neighborhood.[2][1]
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[update], 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.[3]
The first minor planet to be discovered was Ceres in 1801, though it was called a 'planet' at the time and an 'asteroid' soon after; the term minor planet was not introduced until 1841, and was considered a subcategory of 'planet' until 1932.[4] The term planetoid has also been used, especially for larger, planetary objects such as those the IAU has called dwarf planets since 2006.[5][6] Historically, the terms asteroid, minor planet, and planetoid have been more or less synonymous.[5][7] 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.[7] 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.[8] However, for purposes of numbering and naming, the traditional distinction between minor planet and comet is still used.
Cite error: There are <ref group=lower-alpha> tags or {{efn}} templates on this page, but the references will not show without a {{reflist|group=lower-alpha}} template or {{notelist}} template (see the help page).
- ^ a b c Press release, IAU 2006 General Assembly: Result of the IAU Resolution votes, International Astronomical Union, August 24, 2006. Accessed May 5, 2008.
- ^ "IAU 2006 General Assembly: Resolutions 5 and 6" (PDF). IAU. 2006-08-24.
- ^ Cite error: The named reference
MPC-Latest-Published-Datawas invoked but never defined (see the help page). - ^ When did the asteroids become minor planets? Archived 2009-08-25 at the Wayback Machine, James L. Hilton, Astronomical Information Center, United States Naval Observatory. Accessed May 5, 2008.
- ^ a b Planet, asteroid, minor planet: A case study in astronomical nomenclature, David W. Hughes, Brian G. Marsden, Journal of Astronomical History and Heritage 10, #1 (2007), pp. 21–30. Bibcode:2007JAHH...10...21H
- ^ Mike Brown, 2012. How I Killed Pluto and Why It Had It Coming
- ^ a b "Asteroid", MSN Encarta, Microsoft. Accessed May 5, 2008. Archived 2009-11-01.
- ^ Questions and Answers on Planets, additional information, news release IAU0603, IAU 2006 General Assembly: Result of the IAU Resolution votes, International Astronomical Union, August 24, 2006. Accessed May 8, 2008.