page_title: Dwarf planet
section_title: Population of possible dwarf planets
hierarchical_section_title: Dwarf planet / Population of possible dwarf planets
caption_attribution_description: English: Eights with moon orbits, equally scaled, with earth as a comparison.
context_page_description: A dwarf planet is a planetary-mass object that does not dominate its region of space and is not a satellite. That is, it is in direct orbit of the Sun and is massive enough to be plastic – for its gravity to maintain it in a hydrostatically equilibrious shape – but has not cleared the neighborhood around its orbit of other material. The prototype dwarf planet is Pluto.
  The number of dwarf planets in the Solar System is unknown, as determining whether a potential body is a dwarf planet requires close observation. The half-dozen largest candidates have at least one known moon, allowing determination of their masses. The interest of dwarf planets to planetary geologists is that, being differentiated and perhaps geologically active bodies, they are likely to display planetary geology, an expectation borne out by the 2015 New Horizons mission to Pluto and Dawn mission to Ceres.
  The term dwarf planet was coined by planetary scientist Alan Stern as part of a three-way categorization of planetary-mass objects in the Solar System: classical planets, dwarf planets and satellite planets. Dwarf planets were thus conceived of as a subtype of planet, as the name suggests.
context_section_description: The number of dwarf planets in the Solar system is not known. The three objects under consideration during the debates leading up to the 2006 IAU acceptance of the category of dwarf planet – Ceres, Pluto and Eris – are generally accepted as dwarf planets, including by those astronomers who continue to classify dwarf planets as planets. In 2015, Ceres and Pluto were determined to have shapes consistent with hydrostatic equilibrium (and thus with being dwarf planets) by the Dawn and New Horizons missions, respectively, though there is still some question about Ceres. Eris is assumed to be a dwarf planet because it is more massive than Pluto.
  In order of discovery, these three bodies are:
  Ceres  – discovered January 1, 1801 and announced January 24, 45 years before Neptune. Considered a planet for half a century before reclassification as an asteroid. Considered a dwarf planet by the IAU since the adoption of Resolution 5A on August 24, 2006. Confirmation is pending.
  Pluto ♇ –  discovered February 18, 1930 and announced March 13. Considered a planet for 76 years. Explicitly reclassified as a dwarf planet by the IAU with Resolution 6A on August 24, 2006. Five known moons.
  Eris (2003 UB₃₁₃) – discovered January 5, 2005 and announced July 29. Called the "tenth planet" in media reports. Considered a dwarf planet by the IAU since the adoption of Resolution 5A on August 24, 2006, and named by the IAU dwarf-planet naming committee on September 13 of that year. One known moon.
  Due to the 2008 decision to assign the naming of Haumea and Makemake to the dwarf-planet naming committee and their announcement as dwarf planets in IAU press releases, these two bodies are also generally accepted as dwarf planets:
  Haumea (2003 EL₆₁) – discovered by Brown et al. December 28, 2004 and announced by Ortiz et al. on July 27, 2005. Named by the IAU dwarf-planet naming committee on September 17, 2008. Two known moons.
  Makemake (2005 FY₉) – discovered March 31, 2005 and announced July 29. Named by the IAU dwarf-planet naming committee on July 11, 2008. One known moon.
  Four additional bodies meet the criteria of Brown, Tancredi et al. and Grundy et al. for candidate objects:
  Quaoar (2002 LM₆₀) – discovered June 5, 2002 and announced October 7 of that year. One known moon.
  Sedna (2003 VB₁₂) – discovered November 14, 2003 and announced March 15, 2004.
  Orcus (2004 DW) – discovered February 17, 2004 and announced two days later. One known moon.
  Gonggong (2007 OR₁₀) – discovered July 17, 2007 and announced January 2009. Recognized as a dwarf planet by JPL and NASA in May 2016. One known moon.
  Additional bodies have been proposed, such as Salacia and 2002 MS4 by Brown, or Varuna and Ixion by Tancredi et al. Most of the larger bodies have moons, which enables a determination of their masses and thus their densities, which inform estimates as to whether they could be dwarf planets. The largest TNOs that are not known to have moons are Sedna, 2002 MS₄ and 2002 AW197.
  At the time Makemake and Haumea were named, it was thought that trans-Neptunian objects (TNOs) with icy cores would require a diameter of only perhaps 400 km (250 mi)—about 3% of that of Earth—to relax into gravitational equilibrium. Researchers thought that the number of such bodies could prove to be around 200 in the Kuiper belt, with thousands more beyond.
  This was one of the reasons (keeping the roster of 'planets' to a reasonable number) that Pluto was reclassified in the first place. 
  However, research since then has cast doubt on the idea that bodies that small could have achieved or maintained equilibrium under common conditions.
  Individual astronomers have recognized a number of such objects as dwarf planets or as highly likely to prove to be dwarf planets. In 2008, Tancredi et al. advised the IAU to officially accept Orcus, Sedna and Quaoar as dwarf planets, though the IAU did not address the issue then and has not since. In addition, Tancredi considered the five TNOs Varuna, Ixion, 2003 AZ₈₄, 2004 GV₉, and 2002 AW₁₉₇ to be mostly likely dwarf planets as well. In 2012, Stern stated that
caption: The eight largest TNOs with moons (Pluto, Haumea, Makemake, Eris, Quaoar, Gonggong, Orcus and Salacia), with the Earth to scale. Gonggong is written as its provisional designation, 2007 OR10.
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