The term dwarf planet was adopted in 2006 as part of a three-way categorization of bodies orbiting the Sun, brought about by an increase in discoveries of objects farther away from the Sun than Neptune that rivalled Pluto in size, and finally precipitated by the discovery of an even more massive object, Eris The exclusion of dwarf planets from the roster of planets by the IAU has been both praised and criticized; it was said to be the “right decision” by astronomer Mike Brown, who discovered Eris and other new dwarf planets, but has been rejected by Alan Stern who had coined the term dwarf planet in April 1991.
The International Astronomical Union (IAU) currently recognizes five dwarf planets: Ceres; Pluto; Haumea; Makemake; and Eris.Brown criticizes this official recognition: “A reasonable person might think that this means that there are five known objects in the solar system which fit the IAU definition of dwarf planet, but this reasonable person would be nowhere close to correct.”
Another hundred or so known objects in the Solar System are suspected to be dwarf planets. Estimates are that up to 200 dwarf planets will be identified when the entire region known as the Kuiper belt is explored, and that the number may exceed 10,000 when objects scattered outside the Kuiper belt are considered. Individual astronomers recognize several of these and in August 2011 Mike Brown published a list of 390 candidate objects, ranging from “nearly certain” to “possible” dwarf planets. Brown currently identifies ten known trans-Neptunian objects—the four accepted by the IAU plus 2007 OR10, Quaoar, Sedna, Orcus, (307261) 2002 MS4 and Salacia—as “virtually certain”, with another twenty highly likely Stern states that there are more than a dozen known dwarf planets.