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A binary asteroid is a system of two asteroids orbiting their common barycenter. 243 Ida was the first binary asteroid to be identified when the Galileo spacecraft did a flyby in 1993. Since then numerous binary asteroids have been detected. The mass ratio of the two components of a binary system is an important characteristic. Most binary asteroids have a large mass ratio, i.e. a relatively small satellite in orbit around the main component. Systems with a small satellite, or "moon", include 22 Kalliope, 45 Eugenia, 87 Sylvia, 107 Camilla, 121 Hermione, 130 Elektra, 243 Ida, 283 Emma, and 379 Huenna. Some binary systems have a mass ratio near unity, i.e. two components of similar mass. They include 90 Antiope and Hermes. Several theories have been posited to explain the formation of binary-asteroid systems. Recent work suggests that most of them have a significant macro-porosity (a "rubble-pile" interior). The satellites orbiting large main-belt asteroids such as 22 Kalliope, 45 Eugenia or 87 Sylvia could have formed by disruption of a parent body after impact or fission after an oblique impact. Trans-Neptunian binaries may have formed during the formation of the Solar System by mutual capture or three-body interaction. Near-Earth asteroids, which orbit in the inner part of the Solar System, most likely form by spin-up and mass shedding, likely as a result of the YORP effect. A possible explanation for the relatively greater occurrence of binary asteroids near or inside of Earth's orbit was described in the journal Nature (10 June 2008): this work confirms that when solar energy (see YORP effect) spins a “rubble pile” asteroid to a sufficiently fast rate, material is thrown from the asteroid’s equator. This process also exposes fresh material at the poles of the asteroid.〔(Study Puts Solar Spin on Asteroids, their Moons & Earth Impacts ) Newswise, Retrieved 14 July 2008.〕 == See also == * (triple asteroid) * List of minor planets with moons * Yarkovsky–O'Keefe–Radzievskii–Paddack effect (YORP effect) 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「Binary asteroid」の詳細全文を読む スポンサード リンク
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