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Most atoms on Earth came from the interstellar dust and gas from which the Sun and Solar System formed. However, in the space science community, "extraterrestrial materials" generally refers to objects now on Earth that were solidified prior to arriving on Earth. In October 2011, scientists reported that one form of extraterrestrial material, cosmic dust, contains complex organic matter ("amorphous organic solids with a mixed aromatic-aliphatic structure") that could be created naturally, and rapidly, by stars. In February 2014, NASA announced a (greatly upgraded database ) for tracking polycyclic aromatic hydrocarbons (PAHs) in the universe. According to scientists, more than 20% of the carbon in the universe may be associated with PAHs, possible starting materials for the formation of life. PAHs seem to have been formed shortly after the Big Bang, are widespread throughout the universe, and are associated with new stars and exoplanets. ==Categories== To date these fall into a small number of broad categories, namely: # Meteorites too large to vaporize on atmospheric entry but small enough to leave fragments lying on the ground # moon rocks brought back by the Apollo and Luna missions # unmelted micrometeorites typically less than 100 micrometres in diameter collected on Earth and in the Earth's stratosphere # specimens returned from space-borne collection missions like NASA's Long Duration Exposure Facility (LDEF) and the Stardust sample return mission. A minor but notable subset of the materials that make up the foregoing collections were also solidified ''outside of our solar system''. These are often referred to as interstellar materials, some of which are also presolar i.e. they predate the formation of our Solar System. Each of these types of material is treated elsewhere. This entry, therefore, is here primarily to consider the relationship between types of extraterrestrial materials on Earth, as well as the types of extraterrestrial material we'd like to have a closer look at. 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「extraterrestrial materials」の詳細全文を読む スポンサード リンク
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