| 词汇 | meteoroid |
| 释义 | meteoroid noun[ C ] uk /ˈmiː.ti.ə.rɔɪd/ us /ˈmiː.t̬i.ə.rɔɪd/ a piece of rock or other matter in space that has not yet entered the earth's atmosphere流星体 Compare meteorite Astronomy albedo Andromeda Aquarius Aries asteroid galactic galaxy Gemini geostationary geosynchronous observatory orbit orbital Orion penumbra substellar sunspot supergiant supermassive supermoon Examples of meteoroidmeteoroid Even clumps of viable bacteria, if they are introduced as micrometre-sized meteoroids, could survive flash heating in the atmosphere. The asteroids, meteoroids and apparently all comets originated in the explosion of planets (or moons). The sputtering model considered here may require significant modification for the case of highly fluffy and porous meteoroids. Second, the time meteoroids have been travelling in space exposed to cosmic rays is relatively short, typically millions of years. This kinetic energy goes into heating the meteoroid and the surrounding atmosphere. Classical work on meteoroid ablation suggests that these particles should be annihilated by atmospheric deceleration. As the evaporation of molecules from the surface of the meteoroid increases, a vapour cloud starts to form around the meteoroid. Heating of the meteoroid by direct impact causes it to lose mass by fragmentation and, as the temperature rises, evaporation and melting of its surface. Two important lines of evidence that meteoroids originated in an explosion are these. The meteoroids are only heated to their maximum temperatures above their equilibrium temperatures for a short period, of the order of seconds. It was found that meteoroids from cometary sources were typically of porous, aggregate compositions with relatively low densities. Sputtering provides a mechanism for the meteoroids to lose a substantial fraction of their momentum and energy without experiencing extreme heating. This may be the reason why some large meteoroids have been observed at lower heights than expected before total ablation occurs. In general, the detailed atmospheric response to the transit of a very hot meteoroid body is a complicated, non-equilibrium problem. The majority of the kinetic energy of a meteoroid is dissipated by these processes, which are collectively known as ablation. These examples are from corpora and from sources on the web. Any opinions in the examples do not represent the opinion of the Cambridge Dictionary editors or of Cambridge University Press or its licensors. |
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