Editing Kuiper belt (section)

=== Pluto ===
<!-- Please do not add Eris here. Eris is often called a Kuiper belt object but Wikipedia convention treats it strictly as a scattered disc object -->
{{Main|Pluto}}
The discovery of these large KBOs in orbits similar to Pluto's led many to conclude that, aside from its relative size, [[Pluto]] was not particularly different from other members of the Kuiper belt. Not only are these objects similar to Pluto in size, but many also have [[natural satellites]], and are of similar composition (methane and carbon monoxide have been found both on Pluto and on the largest KBOs).<ref name=beyond/> Thus, just as [[Ceres (dwarf planet)|Ceres]] was considered a planet before the discovery of its fellow [[asteroid]]s, some began to suggest that Pluto might also be reclassified.

The issue was brought to a head by the discovery of [[Eris (dwarf planet)|Eris]], an object in the [[scattered disc]] far beyond the Kuiper belt, that is now known to be 27% more massive than Pluto.<ref>{{cite web |title=Dysnomia, the moon of Eris |author=Mike Brown |work=Caltech |url=http://www.gps.caltech.edu/~mbrown/planetlila/moon/index.html |date=2007 |access-date=14 June 2007 |archive-date=17 July 2012 |archive-url=https://web.archive.org/web/20120717010420/http://www.gps.caltech.edu/~mbrown/planetlila/moon/index.html |url-status=live }}</ref> (Eris was originally thought to be larger than Pluto by volume, but the ''[[New Horizons]]'' mission found this not to be the case.) In response, the [[International Astronomical Union]] (IAU) was forced to [[Definition of planet|define what a planet is]] for the first time, and in so doing included in their definition that a planet must have "[[Clearing the neighborhood|cleared the neighbourhood]] around its orbit".<ref>{{cite web |url=http://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf |title=Resolution B5 and B6 |publisher=International Astronomical Union |date=2006 |access-date=2 September 2011 |archive-date=20 June 2009 |archive-url=https://web.archive.org/web/20090620102000/http://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf |url-status=live }}</ref> As Pluto shares its orbit with many other sizable objects, it was deemed not to have cleared its orbit and was thus reclassified from a planet to a [[dwarf planet]], making it a member of the Kuiper belt.

It is not clear how many KBOs are large enough to be dwarf planets. Consideration of the surprisingly low densities of many dwarf-planet candidates suggests that not many are.<ref name="Grundy2019">{{cite journal |last1=Grundy |first1=W.M. |last2=Noll |first2=K.S. |last3=Buie |first3=M.W. |last4=Benecchi |first4=S.D. |last5=Ragozzine |first5=D. |last6=Roe |first6=H.G. |title=The mutual orbit, mass, and density of transneptunian binary Gǃkúnǁʼhòmdímà ({{mp|(229762) 2007 UK|126}}) |journal=Icarus |date=December 2019 |volume=334 |pages=30–38 |doi=10.1016/j.icarus.2018.12.037 |bibcode=2019Icar..334...30G |s2cid=126574999 |url=http://www2.lowell.edu/users/grundy/abstracts/preprints/2019.G-G.pdf |url-status=live |archive-url=https://web.archive.org/web/20190407045339/http://www2.lowell.edu/~grundy/abstracts/preprints/2019.G-G.pdf |archive-date=2019-04-07 }}</ref> {{dp|Orcus}}, Pluto, [[Haumea]], {{dp|Quaoar}}, and [[Makemake]] are accepted by most astronomers; some have proposed other bodies, such as {{dp|Salacia}}, {{mpl|2002 MS|4}},<ref name="BrownList">Mike Brown, [http://www.gps.caltech.edu/~mbrown/dps.html 'How many dwarf planets are there in the outer solar system?'] {{webarchive |url=https://web.archive.org/web/20111018154917/http://www.gps.caltech.edu/~mbrown/dps.html |date=18 October 2011 }} Accessed 15 November 2013</ref> {{mpl|2002 AW|197}}, and {{dp|Ixion}}.<ref name=Tancredi2008>{{Cite journal |last1=Tancredi |first1=G. |last2=Favre |first2=S. A. |doi=10.1016/j.icarus.2007.12.020 |title=Which are the dwarfs in the Solar System? |journal=Icarus |volume=195 |issue=2 |pages=851–862 |year=2008 |bibcode=2008Icar..195..851T}}</ref>