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| ]'s official status as a planet has been a constant subject of controversy since its discovery since the 1990s, when hundreds of smaller objects were found the area of Pluto. | |||
| ===Omission from museum models=== | |||
| Museum and planetarium directors occasionally would create controversy by omitting Pluto from planetary models of the solar system. Some omissions were intentional; the ] reopened after renovation in ] with a model of 8 planets without Pluto. The controversy made headlines in the media at the time. <ref>http://www.space.com/scienceastronomy/solarsystem/tyson_responds_010202.html</ref> | |||
| ===New discoveries ignite debate=== | |||
| ], ], and ]]] | |||
| Continuing advances in telescope technology allowed for further discoveries of ]s in the 21st century, some of comparable size to that of Pluto. In 2002, ] was discovered, with a 1,280 kilometers diameter, making it a bit more than half the size of Pluto. In 2004, the discoverers of ] placed an upper limit of 1,800 kilometers on its diameter, near Pluto's diameter of 2,320 kilometers. | |||
| On ], ], a ] called {{mpl|2003 UB|313}} (nicknamed "Xena") was announced, which on the basis of its ] and simple ] considerations is assumed to be slightly larger than Pluto. This was the largest object discovered in the solar system since ] in 1846. Discoverers and media initially called it the "tenth planet", although there was no official consensus at the time on whether to call it a planet. Others in the astronomy community considered the discovery to be the strongest argument for reclassifying Pluto as a minor planet. | |||
| The last remaining distinguishing feature of Pluto was now its large moon, ], and its atmosphere; these characteristics are probably not unique to Pluto: several other Trans-Neptunian objects have satellites; and {{mp|2003 UB|313}}'s spectrum suggests that it has a similar surface composition to Pluto, as well as a moon (nicknamed "Gabrielle"), discovered in September 2005. Trans-Neptunian object {{mpl|2003 EL|61}} (nicknamed "Santa") has two moons (one of which is nicknamed "Rudolph") and is the fourth largest TNO behind {{mpl|2003 UB|313}}, Pluto, and {{mpl|2005 FY|9}} (nicknamed "Easterbunny"). | |||
| === IAU 2006 decision === | |||
| {{further| ], ], ]}} | |||
| There are three main conditions for an object to be called a 'planet', according to the IAU resolution in 2006. | |||
| #The object must be in orbit around a star, but not be a star itself. | |||
| #The object must be massive enough to be a sphere by its own gravitational force. More specifically, its own gravity should pull it into a shape of ]. | |||
| #It must have ] around its orbit. | |||
| Pluto fails to meet the third condition<ref>{{cite news|url=http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html|title=IAU 2006 General Assembly: Result of the IAU Resolution votes|publisher=IAU|date=24 August 2006|publisher=IAU}}</ref>, but will act as a prototype for a yet to be named ] of ]s. | |||
| === Impact of the IAU decision === | |||
| The news of Pluto's reclassification by the IAU was met with a mixture of bemusement in the press <ref name="geoff2006b">http://www.nytimes.com/2006/08/24/science/space/25pluto.html?ei=5087&en=cfe4d03207c823f2&ex=1172030400&adxnnl=1&excamp=GGGNpluto&adxnnlx=1156820936-x7vi0zUxIJHoKC1TQ0qrMA | |||
| </ref> alongside stories of an astronomer backlash against the decision.<ref name="geoff2006c">http://space.com/scienceastronomy/060824_planet_definition.html</ref> | |||
| Multiple petitions exist online asking the IAU for reinstatement. | |||
| Alan Stern (leader of the ] "]" mission to Pluto) has derided the IAU decision, stating "the definition stinks, for technical reasons."<ref name="geoff2006a">http://msnbc.msn.com/id/14489259/</ref> Stern's contention is that the new definition should also exclude Earth, Mars, Jupiter and Neptune, all of which share their orbits with asteroids<ref name="newscientistspace">http://www.newscientistspace.com/article/dn9846-new-planet-definition-sparks-furore.html</ref>. | |||
| ===Commemoration as a planet=== | |||
| Pluto is shown as a major planet on the ], an inscription on the space probes '']'' and '']'', launched in the early 1970s. The plaque, intended to give information about the origin of the probes to any alien civilization that might in the future encounter the vehicles, includes a diagram of our solar system, showing nine planets. Similarly, an analog image contained within the ], included on the probes '']'' and '']'', also launched in the 1970s includes data regarding Pluto and again shows it as the ninth planet. | |||
| Elements 92, 93, and 94 are named ], ], and ] respectively after the planets ], ], and Pluto. | |||
| ] | |||
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