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| List of gravitationally rounded objects of the Solar System ： ウィキペディア英語版 |
List of gravitationally rounded objects of the Solar System
In 2006, the International Astronomical Union (IAU) defined a planet as a body in orbit around the Sun that was large enough to have achieved hydrostatic equilibrium and to have cleared the neighbourhood around its orbit.〔 ((orig link ))〕 An object in hydrostatic equilibrium is one that is large enough for its gravity to have overcome its internal rigidity, and so relax into a rounded (ellipsoidal) shape. The practical meaning of "cleared the neighborhood" is that a planet is comparatively massive enough for its gravitation to control the orbits of all objects in its vicinity. By the IAU's definition, there are eight planets in the Solar System. Those objects in orbit around the Sun that have achieved hydrostatic equilibrium but have not cleared their neighborhoods are called dwarf planets, and the remainder are termed small Solar System bodies. In addition, the Sun itself and a dozen or so natural satellites are also massive enough to have achieved hydrostatic equilibrium.〔 Apart from the Sun, these bodies are included in the term ''planetary-mass object'', or ''planemo''. All known planetary-mass objects in the Solar System, as well as the Sun, are listed below, along with a sample of the largest objects whose shape has yet to be accurately determined. The Sun's orbital characteristics are listed in relation to the Galactic Center. All other objects are listed in order of their distance from the Sun.
== Sun ==
The Sun is a G-type main-sequence star. It contains almost 99.9 percent of all the mass in the Solar System.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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