Pluto

Pluto
Pluto,   formal designation  134340 Pluto, is the second-most-massive known   dwarf planet  in the   Solar System  (after   Eris) and the tenth-most-massive body observed directly orbiting the   Sun. [h]   <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">Originally classified as the <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  ninth planet<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">from the Sun, Pluto was recategorized as a dwarf planet and <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  plutoid<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">owing to the discovery that it is only one of several large bodies within the <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  Kuiper belt<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">. <sup class="reference" id="cite_ref-wiki-kbo_23-0" style="color:rgb(0,0,0);font-family:sans-serif;line-height:1em;">[i]

<p style="margin-top:0.4em;margin-bottom:0.5em;line-height:19.1875px;color:rgb(0,0,0);font-family:sans-serif;">Like other members of the Kuiper belt, Pluto is composed primarily of rock and ice and is relatively small, approximately one-sixth the mass of the Earth's Moonand one-third its volume. It has an eccentric and highly inclined orbit that takes it from 30 to 49 AU (4.4–7.4 billion km) from the Sun. This causes Pluto to periodically come closer to the Sun than Neptune. As of 2011, it is 32.1 AU from the Sun.<sup class="reference" id="cite_ref-AstDyS-Pluto_24-0" style="line-height:1em;">[15]

<p style="margin-top:0.4em;margin-bottom:0.5em;line-height:19.1875px;color:rgb(0,0,0);font-family:sans-serif;">From its discovery in 1930 until 2006, Pluto was classified as a planet. In the late 1970s, following the discovery of minor planet 2060 Chiron in the outer Solar System and the recognition of Pluto's relatively low mass, its status as a major planet began to be questioned.<sup class="reference" id="cite_ref-ridpath_25-0" style="line-height:1em;">[16]  In the late 20th and early 21st centuries, many objects similar to Pluto were discovered in the outer Solar System, notably the scattered disc object Eris in 2005, which is 27% more massive than Pluto.<sup class="reference" id="cite_ref-hubblesite2007.2F24_26-0" style="line-height:1em;">[17]  On August 24, 2006, the International Astronomical Union (IAU) defined what it means to be a "planet" within the Solar System. This definition excluded Pluto as a planet and added it as a member of the new category "dwarf planet" along with Eris and Ceres.<sup class="reference" id="cite_ref-BBC-Akwagyiram_2005-08-02_27-0" style="line-height:1em;">[18]  After the reclassification, Pluto was added to the list of minor planets and given the number 134340.<sup class="reference" id="cite_ref-Spahr_2006-09-07_28-0" style="line-height:1em;">[19] <sup class="reference" id="cite_ref-Shiga_2006-09-07_29-0" style="line-height:1em;">[20]  A number of scientists hold that Pluto should continue to be classified as a planet, and that other dwarf planets should be added to the roster of planets along with Pluto.<sup class="reference" id="cite_ref-Gray_2008-08-10_30-0" style="line-height:1em;">[21] <sup class="reference" id="cite_ref-31" style="line-height:1em;">[22]

<p style="margin-top:0.4em;margin-bottom:0.5em;line-height:19.1875px;color:rgb(0,0,0);font-family:sans-serif;">Pluto has five known moons, the largest being Charon, discovered in 1978, along with Nix and Hydra, discovered in 2005,<sup class="reference" id="cite_ref-Sicardy2006_32-0" style="line-height:1em;">[23]  and the provisionally named S/2011 (134340) 1, discovered in 2011,<sup class="reference" id="cite_ref-Nasa-Hubble-Pluto_moon_33-0" style="line-height:1em;">[24]  and S/2012 (134340) 1, discovered in 2012.<sup class="reference" id="cite_ref-Showalter_6-1" style="line-height:1em;">[5]  "Vulcan" and "Cerberus" are proposed names, by popular vote, for the newly discovered moons.<sup class="reference" id="cite_ref-AP-20130225_34-0" style="line-height:1em;">[25]  Pluto and Charon are sometimes described as a binary system because the barycenter of their orbits does not lie within either body.<sup class="reference" id="cite_ref-Olkin_2003_35-0" style="line-height:1em;">[26] However, the IAU has yet to formalise a definition for binary dwarf planets, and as such Charon is officially classified as a moon of Pluto.<sup class="reference" id="cite_ref-IAU_Pluto_36-0" style="line-height:1em;">[27]