Editing Definition of planet (section)

=== Pluto ===
{{main|Planets beyond Neptune}}
The long road from planethood to reconsideration undergone by [[Ceres (dwarf planet)|Ceres]] is mirrored in the story of [[Pluto]], which was named a planet soon after its discovery by [[Clyde Tombaugh]] in 1930. Uranus and Neptune had been declared planets based on their circular orbits, large masses and proximity to the ecliptic plane. None of these applied to Pluto, a tiny and icy world in a region of [[gas giant]]s with an orbit that carried it high above the [[ecliptic]] and even inside that of Neptune. In 1978, astronomers discovered Pluto's largest moon, [[Charon (moon)|Charon]], which allowed them to determine its mass. Pluto was found to be much tinier than anyone had expected: only one-sixth the mass of Earth's Moon.  However, as far as anyone could yet tell, it was unique. Then, beginning in 1992, astronomers began to detect large numbers of icy bodies beyond the orbit of Neptune that were similar to Pluto in composition, size, and orbital characteristics. They concluded that they had discovered the hypothesized [[Kuiper belt]] (sometimes called the Edgeworth–Kuiper belt), a band of icy debris that is the source for "short-period" comets—those with orbital periods of up to 200 years.<ref>{{cite journal | author=Weissman, Paul R. | title=The Kuiper Belt|  bibcode=1995ARA&A..33..327W|doi = 10.1146/annurev.aa.33.090195.001551 | year=1995 | journal=Annual Review of Astronomy and Astrophysics | volume=33 | pages=327–357 }}</ref>

Pluto's orbit lays within this band and thus its planetary status was thrown into question.  Many scientists concluded that tiny Pluto should be reclassified as a minor planet, just as Ceres had been a century earlier. [[Michael E. Brown|Mike Brown]] of the [[California Institute of Technology]] suggested that a "planet" should be redefined as "any body in the Solar System that is more massive than the total mass of all of the other bodies in a similar orbit."<ref>{{cite web | author=Brown, Mike. | title=A World on the Edge | work=[[NASA]] Solar System Exploration | url=http://solarsystem.nasa.gov/scitech/display.cfm?ST_ID=105 | access-date=May 25, 2006 | url-status=dead | archive-url=https://web.archive.org/web/20060427091759/http://solarsystem.nasa.gov/scitech/display.cfm?ST_ID=105 | archive-date=April 27, 2006 }}</ref> Those objects under that mass limit would become minor planets. In 1999, [[Brian G. Marsden]] of [[Harvard University]]'s [[Minor Planet Center]] suggested that Pluto be given the [[minor planet number]] 10000 while still retaining its official position as a planet.<ref name=comet>{{cite web
  |title=Is Pluto a giant comet?
  |publisher=Central Bureau for Astronomical Telegrams
  |url=http://www.icq.eps.harvard.edu/ICQPluto.html
  |access-date=July 3, 2011}}</ref><ref>{{cite news|title=Xena becomes Eris&nbsp;– Pluto reduced to a number|author=Kenneth Chang|work= New York Times|url=http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2006/09/15/MNGS8L67LJ1.DTL|access-date=June 18, 2008|date=September 15, 2006}}</ref> The prospect of Pluto's "demotion" created a public outcry, and in response the [[International Astronomical Union]] clarified that it was not at that time proposing to remove Pluto from the planet list.<ref>{{cite web |year=1999 |title=The Status of Pluto:A clarification |work=[[International Astronomical Union]], Press release |url=http://www.bio.aps.anl.gov/~dgore/fun/PSL/Pluto19990203.txt |access-date=May 25, 2006 |url-status=dead |archive-url=https://web.archive.org/web/20060923202926/http://www.bio.aps.anl.gov/~dgore/fun/PSL/Pluto19990203.txt |archive-date=September 23, 2006 }} [http://www.bio.aps.anl.gov/ Copy kept] {{Webarchive|url=https://web.archive.org/web/20081005210115/http://www.bio.aps.anl.gov/ |date=October 5, 2008 }} at the [[Argonne National Laboratory]].</ref><ref>{{cite web|year=1999 |author=Witzgall, Bonnie B. |title=Saving Planet Pluto |work=Amateur Astronomer article |url=http://www.asterism.org/newsletter/l9904-3.htm |access-date=May 25, 2006 |url-status=dead |archive-url=https://web.archive.org/web/20061016080949/http://www.asterism.org/newsletter/l9904-3.htm |archive-date=October 16, 2006 }}</ref>

The discovery of several other [[trans-Neptunian object]]s, such as [[50000 Quaoar|Quaoar]] and [[90377 Sedna|Sedna]], continued to erode arguments that Pluto was exceptional from the rest of the trans-Neptunian population. On July 29, 2005, Mike Brown and his team announced the discovery of a trans-Neptunian object confirmed to be more massive than Pluto,<ref>{{cite web | year=2006 | author=Brown, Mike | title=The discovery of 2003 UB313, the 10th planet.| work= California Institute of Technology| url=http://www.gps.caltech.edu/~mbrown/planetlila/ | access-date=May 25, 2006}}</ref> named [[136199 Eris|Eris]].<ref>{{cite web | year=2005 |author1=M. E. Brown |author2=C. A. Trujillo |author3=D. L. Rabinowitz | title=DISCOVERY OF A PLANETARY-SIZED OBJECT IN THE SCATTERED KUIPER BELT| work= The American Astronomical Society.| url=http://www.gps.caltech.edu/%7Embrown/papers/ps/xena.pdf | access-date=August 15, 2006}}</ref>

In the immediate aftermath of the object's discovery, there was much discussion as to whether it could be termed a "[[tenth planet]]". NASA even put out a press release describing it as such.<ref>{{cite web|title=NASA-Funded Scientists Discover Tenth Planet|work=Jet Propulsion Laboratory|url=http://www.nasa.gov/vision/universe/solarsystem/newplanet-072905.html|year=2005|access-date=February 22, 2007|archive-date=March 19, 2015|archive-url=https://web.archive.org/web/20150319203306/http://www.nasa.gov/vision/universe/solarsystem/newplanet-072905.html|url-status=dead}}</ref> However, acceptance of Eris as the tenth planet implicitly demanded a definition of planet that set Pluto as an arbitrary minimum size. Many astronomers, claiming that the definition of planet was of little scientific importance, preferred to recognise Pluto's historical identity as a planet by "[[grandfathering]]" it into the planet list.<ref>{{cite web|title=Topic&nbsp;— First Mission to Pluto and the Kuiper Belt; "From Darkness to Light: The Exploration of the Planet Pluto"|author= Bonnie Buratti|work=Jet Propulsion Laboratory|url=http://www.jpl.nasa.gov/events/lectures/nov05.cfm|year=2005|access-date=February 22, 2007}}</ref>