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A planetary body or planetary object is any secondary body in the Solar System that is geologically differentiated or in hydrostatic equilibrium and thus has a planet-like geology: a planet, dwarf planet, or the larger moons and asteroids. In 2002, planetary scientists Alan Stern and Harold Levison proposed the following algorithm to determine whether an object in space satisfies the definition for a planetary body.〔 The body must: # Be low enough in mass that at no time (past or present) can it generate energy in its interior due to any self-sustaining nuclear fusion chain reaction. # Be large enough that its shape becomes determined primarily by gravity rather than mechanical strength or other factors (such as surface tension or rotation rate) in less than a Hubble time, so that the body would on this timescale or shorter reach a state of hydrostatic equilibrium in its interior. This definition excludes brown dwarfs and stars, as well as small bodies such as planetesimals. ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「planetary body」の詳細全文を読む スポンサード リンク
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