Editing Kuiper belt (section)

== Largest KBOs ==
{{see also|List of the brightest Kuiper belt objects}}
<!-- Please do not add Eris here. Eris is often called a Kuiper belt object but Wiki convention treats it strictly as a scattered disc object -->

Since 2000, a number of KBOs with diameters of between 500 and {{convert|1500|km|0|abbr=on}}, more than half that of Pluto (diameter 2370&nbsp;km), have been discovered. [[50000 Quaoar|Quaoar]], a classical KBO discovered in 2002, is over 1,200&nbsp;km across. {{dp|Makemake}} and {{dp|Haumea}}, both announced on 29 July 2005, are larger still. Other objects, such as [[28978 Ixion]] (discovered in 2001) and [[20000 Varuna]] (discovered in 2000), measure roughly {{convert|600–700|km|0|abbr=on}} across.<ref name=beyond/>

=== 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>

=== Satellites ===
The six largest TNOs ([[Eris (dwarf planet)|Eris]], [[Pluto]], [[225088 Gonggong|Gonggong]], [[Makemake]], [[Haumea]] and [[50000 Quaoar|Quaoar]]) are all known to have satellites, and two of them have more than one. A higher percentage of the larger KBOs have satellites than the smaller objects in the Kuiper belt, suggesting that a different formation mechanism was responsible.<ref>{{cite journal |doi=10.1086/501524 |last1=Brown |first1=M. E. |author-link=Michael E. Brown |last2=Van Dam |first2=M. A. |last3=Bouchez |first3=A. H. |last4=Le Mignant |first4=D. |last5=Campbell |first5=R. D. |last6=Chin |first6=J. C. Y. |last7=Conrad |first7=A. |last8=Hartman |first8=S. K. |last9=Johansson |first9=E. M. |last10=Lafon |first10=R. E. |last11=Rabinowitz |first11=D. L. Rabinowitz |last12=Stomski |first12=P. J. Jr. |last13=Summers |first13=D. M. |last14=Trujillo |first14=C. A. |last15=Wizinowich |first15=P. L. |year=2006 |title=Satellites of the Largest Kuiper Belt Objects |journal=The Astrophysical Journal |volume=639 |issue=1 |pages=L43–L46 |arxiv=astro-ph/0510029 |bibcode=2006ApJ...639L..43B |s2cid=2578831 |url=http://web.gps.caltech.edu/~mbrown/papers/ps/gab.pdf |access-date=19 October 2011 |ref={{sfnRef|Brown Van Dam et al.|2006}} |archive-date=28 September 2018 |archive-url=https://web.archive.org/web/20180928185647/http://web.gps.caltech.edu/~mbrown/papers/ps/gab.pdf |url-status=live }}</ref> There are also a high number of binaries (two objects close enough in mass to be orbiting "each other") in the Kuiper belt. The most notable example is the Pluto–Charon binary, but it is estimated that around 11% of KBOs exist in binaries.<ref>{{cite journal |first1=C.B. |last1=Agnor |first2=D.P. |last2=Hamilton |title=Neptune's capture of its moon Triton in a binary-planet gravitational encounter |journal=Nature |volume=441 |date=2006 |pages=192–4 |url=http://www.astro.umd.edu/~hamilton/research/reprints/AgHam06.pdf |doi=10.1038/nature04792 |pmid=16688170 |issue=7090 |bibcode=2006Natur.441..192A |s2cid=4420518 |access-date=9 July 2010 |archive-date=3 November 2013 |archive-url=https://web.archive.org/web/20131103235809/http://www.astro.umd.edu/~hamilton/research/reprints/AgHam06.pdf |url-status=live }}</ref>