Editing Planets beyond Neptune (section)

== Discovery of further trans-Neptunian objects ==

{{See also|Kuiper belt#History|l1=History of the Kuiper belt}}
After the discovery of Pluto and Charon, no more [[trans-Neptunian object]]s (TNOs) were found until [[15760 Albion]] in 1992.<ref>{{cite web|author=Minor Planet Center|title=Circular No. 5611 |date= 1992 |url=http://www.cbat.eps.harvard.edu/iauc/05600/05611.html|access-date=2011-07-05|archive-url = https://web.archive.org/web/20080504183122/http://cfa-www.harvard.edu/iau/iauc/05600/05611.html |archive-date = May 4, 2008}}</ref> Since then, thousands of such objects have been discovered. Most are now recognized as part of the [[Kuiper belt]], a swarm of icy bodies left over from the Solar System's formation that orbit near the [[plane of the ecliptic|ecliptic plane]] just beyond Neptune. Though none were as large as Pluto, some of these distant trans-Neptunian objects, such as [[90377 Sedna|Sedna]], were initially described in the media as "new planets".<ref>{{cite news |title= Astronomers discover 'new planet' |work= BBC News |url=http://news.bbc.co.uk/1/hi/sci/tech/3511678.stm |access-date= 2008-06-20 | date=2004-03-15}}</ref>

In 2005, astronomer [[Michael E. Brown|Mike Brown]] and his team announced the discovery of {{mp|2003 UB|313}} (later named {{dp|Eris}} after the Greek goddess of discord and strife), a trans-Neptunian object then thought to be just barely larger than Pluto.<ref>{{cite web|title=Circular No. 8747 |author= Central Bureau for Astronomical Telegrams, International Astronomical Union |url=http://www.cbat.eps.harvard.edu/iauc/08700/08747.html |date= 2006 |access-date= 2011-07-05|archive-url = https://web.archive.org/web/20070205035336/http://www.cfa.harvard.edu/iau/special/08747.pdf |archive-date = February 5, 2007|url-status=dead}}</ref> Soon afterwards, a NASA [[Jet Propulsion Laboratory]] press release described the object as the "tenth planet".<ref>{{cite web |title=NASA-Funded Scientists Discover Tenth Planet |publisher=Jet Propulsion Laboratory |url=http://www.jpl.nasa.gov/news/news-print.cfm?release=2005-126 |date=2005 |access-date=2007-02-22 |url-status=dead |archive-url=https://web.archive.org/web/20110721191652/http://www.jpl.nasa.gov/news/news-print.cfm?release=2005-126 |archive-date=2011-07-21 }}</ref>

Eris was never officially classified as a planet, and the [[IAU definition of planet|2006 definition of planet]] defined both Eris and Pluto not as planets but as dwarf planets because they have not [[clearing the neighbourhood|cleared their neighbourhoods]].<ref name=IAU/> They do not orbit the Sun alone, but as part of a population of similarly sized objects. Pluto itself is now recognized as being a member of the Kuiper belt and the largest dwarf planet, larger than the more massive Eris.

A number of astronomers, most notably [[Alan Stern]], the head of NASA's ''[[New Horizons]]'' mission to Pluto, contend that the IAU's definition is flawed, and that Pluto and Eris, and all large trans-Neptunian objects, such as {{Dp|Makemake}}, {{Dp|Sedna}}, {{Dp|Quaoar}}, {{Dp|Gonggong}} and {{Dp|Haumea}}, should be considered planets in their own right.<ref>{{Cite web |last=Stern |first=Alan |date=September 8, 2006 |title=Unabashedly Onward to the Ninth Planet |url=http://www.spacedaily.com/reports/Unabashedly_Onward_to_the_Ninth_Planet_999.html |access-date=2008-06-25 |website=SpaceDaily.com |publisher=NASA}}</ref> However, the discovery of Eris did not rehabilitate the Planet&nbsp;X theory because it is far too small to have significant effects on the outer planets' orbits.<ref>{{Cite web |last=C. Jewitt |first=David |author-link=David C. Jewitt |date=2021 |title=Dave Jewitt: Planets IX and X |url=http://www2.ess.ucla.edu/~jewitt/kb/planetx.html |access-date=2024-09-11 |website=UCLA - Earth, Planetary & Space Sciences}}</ref>