::Trans-Neptunian object


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{{#invoke:Sidebar|sidebar}} A trans-Neptunian object (TNO; also written transneptunian object) is any minor planet in the Solar System that orbits the Sun at a greater average distance (semi-major axis) than Neptune, 30 astronomical units (AU). Twelve minor planets<ref name="count" group=nb>2003 SS422 is excluded from the count because it has an observation arc of only 76 days and hence its semi-major axis is not securely known.</ref> with a semi-major axis greater than 150 AU and perihelion greater than 30 AU are known, which are called extreme trans-Neptunian objects (ETNOs).<ref name="Marcos2014">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref>

The first trans-Neptunian object to be discovered was Pluto in 1930. It took until 1992 to discover a second trans-Neptunian object orbiting the Sun directly, (15760) 1992 QB1. As of July 2015 over 1,650 trans-Neptunian objects appear on the Minor Planet Center's List Of Transneptunian Objects.<ref name=TNOs>IAU Minor Planet Center List Of Transneptunian Objects</ref><ref name="jpl-TNOs"/> Of these TNOs, 1471 have a perihelion further out than Neptune (30.1 AU).<ref name="perihelion30au"/> As of November 2009, two hundred of these have their orbits well-enough determined that they have been given a permanent minor planet designation.<ref name=TNOs/><ref>List of Centaurs and Scattered Disc objects</ref>

The largest known trans-Neptunian object is Pluto, followed by Eris, Makemake, 2007 OR10 and Haumea. The Kuiper belt, scattered disk, and Oort cloud are three conventional divisions of this volume of space,<ref name=Remo>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> though treatments vary and a few objects such as Sedna do not fit easily into any division.Unknown extension tag "ref"

Trans-Neptunian object sections
Intro   History    Distribution and classification    Notable trans-Neptunian objects   Putative trans-Neptunian objects of planetary size  Physical characteristics   See also  Notes  References   External links  

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