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The ordinary chondrites (sometimes called the O chondrites) are a class of stony chondritic meteorites. They are by far the most numerous group and comprise about 87% of all finds.〔(Natural History Museum, meteorite catalogue )〕 Hence, they have been dubbed "ordinary". The ordinary chondrites are thought to have originated from three parent asteroids, with the fragments making up the H chondrite, L chondrite and LL chondrite groups respectively.〔(NASA (YouTube) – Dr. David Kring – Asteroid Initiative Workshop Cosmic Explorations Speakers Session )〕 ==Origin== It is suspected that they are not representative of typical asteroid parent bodies, but rather of a select few which are advantageously placed to send impact fragments to Earth-crossing orbits. Such positions are e.g. near Kirkwood gaps and/or secular resonances in the main asteroid belt. In fact, only the one rather insignificant asteroid 3628 Božněmcová has been identified to have a spectrum close to the ordinary chondrites. A probable parent body of the H chondrites (comprising about 46% of the ordinary chondrites) is 6 Hebe, but its spectrum is dissimilar due to what is likely a metal impact melt component. It is likely that the ordinary chondrites comprise a detailed sample of but a few select asteroids which happen to have been in the right place at the right time to send many fragments toward Earth at the present moment in solar system history. On the other hand, observations of 243 Ida by the Galileo spacecraft found weathering of Ida's surface, and the reflection spectra of freshly exposed parts of the surface resembled that of OC meteorites, while the older regions matched the spectra of common S-type asteroids. 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「Ordinary chondrite」の詳細全文を読む スポンサード リンク
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