What is a Dwarf Planet?
A dwarf planet is a new category of celestial body created by the International Astronomers Union in 2006. It includes celestial bodies massive enough to be spherical, in orbit around the Sun, which are not satellites. The crucial factor dividing a planet from a dwarf planet is that a planet must have succeeded in clearing the area of its orbit from debris and other objects, whereas a dwarf planet has not. When the category of dwarf planet was created, three bodies were immediately classified as such: Ceres, the largest asteroid, now a dwarf planet; Pluto, in the Kuiper belt, demoted from the status of planet; and Eris, a scattered disc object located far beyond the orbit of Pluto. It was the discovery of Eris that partially prompted the International Astronomers Union to more precisely define what they meant by the word “planet.” Despite the name “dwarf planet”, dwarf planets are not considered a subset of planets, but rather in a different category altogether. Objects still smaller t
When the final vote on the definition of “planet” was made, and the eight dominant bodies in the solar system were declared (quite rationally) a class separate from the others, a new class of objects was defined. The “dwarf planets” are all of those objects which are not one of the eight dominant bodies (Mercury through Neptune) yet still, at least in one way, resemble a planet. The best definition heard so far is that a dwarf planet is something that looks like a planet, but is not a planet. The dwarf planets are bodies in the solar system which are large enough to become round due to their own gravitational attraction. Why do astronomers care about round? If you place a boulder in space it will just stay whatever irregular shape it is. If you add more boulders to it you can still have an irregular pile. But if you add enough boulders to the pile they will eventually pull themselves into a round shape. This transition from irregularly shaped to round objects is important in the solar
Explanations of this new class along with a complete list of the likely candidates that meet the criteria for dwarf planethood. • The eight planets An explanation of why astronomers decided that Pluto should no longer be considered a planet and why eight is a good number of planets. • Eris The largest dwarf planet, and the object whose discovery prompted the decision to reclassify all of these objects, including Pluto, as dwarf planets. • A Requiem for Xena A farewell to the former planet formerly known as Xena, now officially known as the dwarf planet named Eris. • 2003 EL61 = Haumea Information about Haumea, a rapidly spinning Pluto-sized football-shaped ice-coated deformed rock in the outer solar system with a family of icy debris around it. • Sedna the first of a new class of objects beyond the Kuiper belt and a fossilized record from the birth of the solar system. • Orcus Pluto’s slightly smaller twin. • Quaoar The first to be discovered (in 2002) of the truly gigantic Kuiper belt
