Editing Planets beyond Neptune (section)

===Probability===

Even without gravitational evidence, Mike Brown, the discoverer of Sedna, has argued that Sedna's 12,000-year orbit means that probability alone suggests that an Earth-sized object exists beyond Neptune. Sedna's orbit is so eccentric that it spends only a small fraction of its orbital period near the Sun, where it can be easily observed. This means that unless its discovery was a freak accident, there is probably a substantial population of objects roughly Sedna's diameter yet to be observed in its orbital region.<ref name="Mike" /> Mike Brown noted that
{{blockquote|Sedna is about three-quarters the size of Pluto. If there are sixty objects three-quarters the size of Pluto [out there] then there are probably forty objects the size of Pluto ... If there are forty objects the size of Pluto, then there are probably ten that are twice the size of Pluto. There are probably three or four that are three times the size of Pluto, and the biggest of these objects ... is probably the size of Mars or the size of the Earth.<ref name="wgbh">{{Cite web |last=Brown |first=Michael |date=11 April 2007 |title=Pluto and the outer solar system |url=http://forum.wgbh.org/wgbh/forum.php?lecture_id=3710 |url-status=dead |archive-url=https://web.archive.org/web/20080103202810/http://forum.wgbh.org/wgbh/forum.php?lecture_id=3710 |archive-date=2008-01-03 |access-date=2008-07-13 |series=Lowell Lectures in Astronomy |publisher=Museum of Science, Boston / WGBH |place=Boston, MA}}</ref><ref>{{cite AV media |first=Mike |last=Brown |date=August 2008 |title=Pluto, Eris, and the dwarf planets of the outer solar system |type=academic talk |publisher=Smithsonian |time=50ᵐ |url=https://www.youtube.com/watch?v=WHNO079G1i8&t=3135 |url-status=live |access-date=2 January 2019 |archive-url=https://ghostarchive.org/varchive/youtube/20211114/WHNO079G1i8 |archive-date=2021-11-14 |via=[[YouTube]]}}{{cbignore}} The argument about dwarf planet sizes beyond Neptune is 50ᵐ into his talk. The WGBH link doesn't work; view on YouTube.</ref><ref>{{cite web |title=Planet 10? Another Earth-size world may lurk in the outer solar system |date=22 June 2017 |website=[[Space.com]] |url=https://www.space.com/37295-possible-planet-10.html}}</ref>}}

However, Brown notes that even though it might approach or exceed Earth in size, should such an object be found it would still be a "dwarf planet" by the current definition, because it would not have cleared its neighbourhood sufficiently.<ref name=wgbh/>