Dwarf planet
Dwarf planets are one of the International Astronomical Union ( IAU) defined in Prague on 24 August 2006 class of celestial bodies in the solar system moving in an orbit around the sun. As the planet they have sufficient mass to achieve the hydrostatic equilibrium ( ie, the shape of a sphere to assume subject to deformation to a spheroid by the self-rotation ). Unlike planets have their orbits but not cleared by other objects. Dwarf planets beyond Neptune's orbit constitute the subclass of Plutoiden.
With Ceres, Pluto, Haumea, Makemake and Eris is currently (2012 ) five celestial bodies are considered dwarf planets. In addition, there are several hundred other objects in the solar system, which may meet the definition of the IAU, but are not officially recognized as a dwarf planet because of missing data.
Definition
The category of dwarf planet is one of three categories, the IAU has set for the solar system. The properties are spread out thereafter on:
The original name " plutons " for a new sub-class of dwarf planets, which run beyond Neptune around the sun, came primarily in the community of geoscientists who already use the term otherwise (see Pluton (geology) ), upon opposition and was discarded. However, the Latin form Plutoiden, a proposal by members of the IAU Committee for naming small celestial bodies, for the time being could not prevail, the first unnamed subclass but was created anyway. In June 2008, the Executive Committee of the IAU has this subclass finally called at its meeting in Oslo with Plutoiden.
Classified dwarf planet
Currently (2012 ) classified five celestial body by the IAU as a dwarf planet. Another overview provides the list of dwarf planets of the solar system.
Dwarf planet in the asteroid belt
Trans-Neptunian dwarf planets ( Plutoiden )
Candidates
Several hundred other objects in the solar system, both in the asteroid belt (about Vesta, Pallas, Hygeia ) and in the trans-Neptunian region ( about Orcus, Quaoar, Sedna or Varuna ) could also fall into the category of dwarf planets. The IAU working on the classification of other dwarf planets. The candidates are guided on a watch list. At present, the present observations for these objects are still not sufficient to be able to ensure that they are in hydrostatic equilibrium.
Criticism
The definition is controversial because critics repeatedly report and interpret the final criterion differently. Thus, the earth, classified as a planet, still about ten thousand objects in their path. Also in Jupiter's orbit are still many objects ( Trojans). The Earth as Jupiter have their orbits yet cleared, because it deals with an the mass ratio of main body remaining bodies in the same orbit. This ratio is so large that the mass fraction of the rest of the body in the orbit of this planet is negligible in today classified as a planet celestial bodies; it is in the case of the earth only 1/1.700.000. The definition refers only to the solar system and not generally on planetary systems. This is also a point of criticism.