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Cosmic dust is dust which exists in space. Most cosmic dust particles are between a few molecules to 0.1 µm in size. A smaller fraction of all dust in space consists of larger refractory minerals that condensed as matter left the stars. It is called "stardust" and is included in a separate section below. The dust density in the local interstellar medium of the Local Bubble is approximately 10−6 × dust grain/m3 with each grain having a mass of approximately 10−17 kg.〔("Applications of the Electrodynamic Tether to Interstellar Travel" ) Gregory L. Matloff, Less Johnson, February, 2005〕 Cosmic dust can be further distinguished by its astronomical location: intergalactic dust, interstellar dust, interplanetary dust (such as in the zodiacal cloud) and circumplanetary dust (such as in a planetary ring). In the Solar System, interplanetary dust causes the zodiacal light. Sources of Solar System dust include comet dust, asteroidal dust, dust from the Kuiper belt, and interstellar dust passing through the Solar System. The terminology has no specific application for describing materials found on the planet Earth except for dust that has demonstrably fallen to Earth. By one estimate, as much as 40,000 tons of cosmic dust reaches the Earth's surface every year.〔"(Spacecraft Measurements of the Cosmic Dust Flux )", Herbert A. Zook. 〕 In October 2011, scientists reported that cosmic dust contains complex organic matter ("amorphous organic solids with a mixed aromatic–aliphatic structure") that could be created naturally, and rapidly, by stars. On August 14, 2014, scientists announced the collection of possible interstellar dust particles from the Stardust spacecraft since returning to Earth in 2006. ==Study and importance== Cosmic dust was once solely an annoyance to astronomers, as it obscures objects they wish to observe. When infrared astronomy began, those dust particles were observed to be significant and vital components of astrophysical processes. Their analysis can reveal information about phenomena like the formation of our Solar System. For example, cosmic dust can drive the mass loss when a star is nearing the end of its life, play a part in the early stages of star formation, and form planets. In our Solar System, dust plays a major role in the zodiacal light, Saturn's B Ring spokes, the outer diffuse planetary rings at Jupiter, Saturn, Uranus and Neptune, and comets. The study of dust is a many-faceted research topic that brings together different scientific fields: physics (solid-state, electromagnetic theory, surface physics, statistical physics, thermal physics), fractal mathematics, chemistry (chemical reactions on grain surfaces), meteoritics, as well as every branch of astronomy and astrophysics. These disparate research areas can be linked by the following theme: the cosmic dust particles evolve cyclically; chemically, physically and dynamically. The evolution of dust traces out paths in which the Universe recycles material, in processes analogous to the daily recycling steps with which many people are familiar: production, storage, processing, collection, consumption, and discarding. Observations and measurements of cosmic dust in different regions provide an important insight into the Universe's recycling processes; in the clouds of the diffuse interstellar medium, in molecular clouds, in the circumstellar dust of young stellar objects, and in planetary systems such as our Solar System, where astronomers consider dust as in its most recycled state. The astronomers accumulate observational ‘snapshots’ of dust at different stages of its life and, over time, form a more complete movie of the Universe's complicated recycling steps. The detection of cosmic dust points to another facet of cosmic dust research: dust acting as photons. Once cosmic dust is detected, the scientific problem to be solved is an inverse problem to determine what processes brought that encoded photon-like object (dust) to the detector. Parameters such as the particle's initial motion, material properties, intervening plasma and magnetic field determined the dust particle's arrival at the dust detector. Slightly changing any of these parameters can give significantly different dust dynamical behavior. Therefore one can learn about where that object came from, and what is (in) the intervening medium. 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「cosmic dust」の詳細全文を読む スポンサード リンク
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