Cosmic dust

Japanese: 宇宙塵 - うちゅうじん（英語表記）cosmic dust

(1) Fine particles of matter scattered throughout space. They come in a variety of sizes, and those found in interstellar space are produced in the atmospheres of low-temperature giant stars and in the gases emitted by novae and supernovae. Many of these particles are about the wavelength of light and cause color excess. Clouds of cosmic dust are observed as dark nebulae. In the solar system, some are produced by the breakup of comets and some appear as meteors. Larger particles are attached to the tails of asteroids, and smaller particles are thought to be connected to gas molecules.
(2) Tiny fragments of meteorites and other celestial bodies that fall to Earth. On land, they are difficult to distinguish because they mix with the soil, but on the deep sea floor, there is little clay transported from the land, and a considerable amount of space dust is mixed into the sediments. In recent years, based on the age and thickness of the sediments on the deep sea floor, it has been discovered that the rate of accumulation is extremely slow, about 1 mm per 1,000 years. In addition, the amount of space dust that falls to Earth has not changed much from tens of thousands of years ago to the present, and it is said that it is about 10,000 tons per day.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

(1) 宇宙空間に散在する微粒物質。大きさは種々で，恒星間にあるものは低温度の巨星の大気，新星や超新星の放出ガス中でつくられ，光の波長程度のものが多く色超過の原因となる。また宇宙塵の雲は暗黒星雲として観測される。太陽系内では，彗星の分解によって生成されるものや，流星として現れるものがある。大きなものは小惑星の末席に連なり，小さな微粒子は気体分子につながるとみられる。
(2) 隕石など地球上に落下する他の天体の微細な破片。陸上では土と混ざって見分けにくいが，深海底では陸地から運ばれる粘土などが少なく，堆積物にはかなりの量の宇宙塵が混ざっている。近年深海底の堆積物の年代と厚さから，その堆積する速さが 1000年に 1mm内外できわめて遅いことがわかった。また，地球上に落下する宇宙塵の量は数万年前から今日まであまり変化がなく，1日 1万t内外という説がある。

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