Editing Trans-Neptunian object (section)

{{Short description|Solar system objects beyond Neptune}}
{{Use dmy dates|date=August 2024}}
{{About|solar system objects beyond Neptune|hypothetical planets| Planets beyond Neptune}}
{{TNO}}

A '''trans-Neptunian object''' ('''TNO'''), also written '''transneptunian object''',<ref>{{Cite web|url=https://www.eso.org/public/images/eso9415a/|title = Transneptunian object 1994 TG2}}</ref> is any [[minor planet]] in the [[Solar System]] that [[orbit]]s the [[Sun]] at a greater average distance than [[Neptune]], which has an orbital [[semi-major axis]] of 30.1 [[astronomical unit]]s (AU).

Typically, TNOs are further divided into the [[Classical Kuiper belt object|classical]] and [[Resonant trans-Neptunian object|resonant]] objects of the [[Kuiper belt]], the [[scattered disc]] and [[detached object]]s with the [[sednoid]]s being the most distant ones.{{refn|The literature is inconsistent in the use of the phrases "scattered disc" and "Kuiper belt". For some, they are distinct populations; for others, the scattered disk is part of the Kuiper belt, in which case the low-eccentricity population is called the "classical Kuiper belt". Authors may even switch between these two uses in a single publication.<ref>McFadden, Weissman, & Johnson (2005). ''Encyclopedia of the Solar System'', footnote p. 584</ref>|group="nb"|name="KB"}} As of February 2025, the [[List of minor planets#Main index|catalog of minor planets]] contains [[List of trans-Neptunian objects|1006 numbered]] and more than [[List of unnumbered trans-Neptunian objects|4000 unnumbered TNOs]].<ref name="MPC-List-TNOs"/><ref name="MPC-List-Cen-and-SDO"/><ref name="TNO-list-Johnstons"/><ref name="JPL-TNO-query-I"/><ref name="JPL-TNO-query-II"/> However, nearly 5900 objects with semimajor axis over 30 AU are present in the MPC catalog, with 1009 being numbered.

The first trans-Neptunian object to be [[Planets beyond Neptune|discovered was Pluto]] in 1930. It took until 1992 to discover a second trans-Neptunian object orbiting the Sun directly, [[15760 Albion]]. The most massive TNO known is [[Eris (dwarf planet)|Eris]], followed by [[Pluto]], {{dp|Haumea}}, {{dp|Makemake}}, and {{dp|Gonggong}}. More than [[Minor-planet moon#Trans-Neptunian objects|80 satellites]] have been discovered in orbit of trans-Neptunian objects. TNOs vary in [[#Colours|color]] and are either grey-blue (BB) or very red (RR). They are thought to be composed of mixtures of rock, [[amorphous carbon]] and volatile ices such as water and [[methane]], coated with [[tholin]]s and other organic compounds.

Twelve minor planets with a semi-major axis greater than 150&nbsp;AU and [[perihelion]] greater than 30&nbsp;AU are known, which are called [[extreme trans-Neptunian object]]s (ETNOs).<ref name="Marcos2014">{{cite journal|author=C. de la Fuente Marcos|author2=R. de la Fuente Marcos|title=Extreme trans-Neptunian objects and the Kozai mechanism: signalling the presence of trans-Plutonian planets|journal=[[Monthly Notices of the Royal Astronomical Society]]|volume=443|issue=1|pages=L59–L63|arxiv=1406.0715|bibcode=2014MNRAS.443L..59D|doi=10.1093/mnrasl/slu084|date=September 1, 2014|doi-access=free }}</ref>