Group 7 Dwarf Planets

about 30 percent smaller than earth's moon,pluto is now considered a dwarf planet, class of orbiting bodies that includes eris,ceres and perhaps nearly a dozen other bodies. pluto orbits the kuiper belt,a region of the solar systemt extenting beyond the planets and thought to be origin of many coments.

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A dwarf planet, as defined by the International Astronomical Union (IAU), is a celestial body in direct orbit of the Sun[1] that is massive enough that its shape is controlled by gravitational forces rather than mechanical forces (and thus an ellipsoid in shape), but has not cleared its neighboring region of other objects.[2][3] More explicitly, it is a planetary-mass object—having sufficient mass to overcome its compressive strength and achieve hydrostatic equilibrium—but not a satellite.

The term dwarf planet was adopted in 2006 as part of a three-way categorization of bodies orbiting the Sun,[1] brought about by an increase in discoveries of trans-Neptunian objects that rivaled Pluto in size, and finally precipitated by the discovery of an even more massive object, Eris.[4] This classification states that bodies large enough to have cleared the neighbourhood of their orbit are defined as planets, while those that are not massive enough to be rounded by their own gravity are defined as small Solar System bodies. Dwarf planets come in between. 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 Mike Brown,[5][6][7] who discovered Eris and the other new dwarf planets accepted by the IAU, but has been rejected by Alan Stern,[8][9] who had coined the term dwarf planet in 1990.[10]

The IAU currently recognizes five dwarf planets in the Solar System: Ceres, Pluto, Haumea, Makemake, and Eris.[11] However, only two of these bodies, Ceres and Pluto, have been observed in enough detail to demonstrate that they fit the definition. Eris has been accepted as a dwarf planet because it is more massive than Pluto. The IAU subsequently decided that unnamed trans-Neptunian objects with an absolute magnitude brighter than +1 (and hence a mathematically delimited minimum diameter of 838 km)[12] are to be named under the assumption that they are dwarf planets.[13] The only two such objects known at the time, Makemake and Haumea, went through this naming procedure and were declared to be dwarf planets.

It is suspected that at least another fifty known objects in the Solar System are dwarf planets. Estimates are that up to 200 dwarf planets may be found when the entire region known as the Kuiper belt is explored, and that the number might be as high as 2,000 when objects scattered outside the Kuiper belt are considered.[14] Mike Brown published in August 2011 his own list of 390 candidate objects, organized in categories from "nearly certainly" to "possibly" meeting the IAU's criteria, along with his classification methodology.[15] Brown identifies nine known objects – the five mentioned plus 2007 OR10, Sedna, Quaoar, and Orcus – as "virtually certain",[16] with another two dozen highly likely,[16] and there are probably a hundred or so such objects in total.[16]

The classification of bodies in other planetary systems with the characteristics of dwarf planets has not yet been addressed.[17]

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