exosphere

exospherical /ek'seuh sfer"i keuhl, -sfear"-/, exospheric, adj.
/ek"soh sfear'/, n.
the highest region of the atmosphere, where the air density is so low that a fast-moving air molecule is more than 50 percent likely to escape from the atmosphere instead of hitting other molecules.
[1950-55; EXO- + -SPHERE]

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      outermost region of a planet's atmosphere, where molecular densities are low and the probability of collisions between molecules (molecule) is very small. The base of the exosphere is called the critical level of escape (escape velocity) because, in the absence of collisions, lighter, faster-moving atoms such as hydrogen and helium may attain velocities that allow them to escape the planet's gravitational field. Most molecules, however, have velocities considerably lower than the escape velocity, so their rate of escape to outer space is quite low.

      The Earth's exosphere begins about 500 km (300 miles) above the terrestrial surface and extends out through the magnetosphere and beyond to the interplanetary medium. Temperatures in the Earth's exosphere remain constant with altitude, averaging about 1500 K. The Earth's exosphere contains the hydrogen geocorona and the Van Allen radiation belts.

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Universalium. 2010.

Look at other dictionaries:

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  • exosphère — [ ɛgzɔsfɛr ] n. f. • 1951; de exo et (atmo)sphère ♦ Géophys. Partie la plus élevée de l atmosphère (au dessus de 750 km) où les molécules les plus légères échappent à la pesanteur et sont attirées vers l espace intersidéral. ● exosphère nom… …   Encyclopédie Universelle

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  • Exosphere — Earth atmosphere diagram showing the exosphere and other layers. The layers are to scale. From Earth s surface to the top of the stratosphere (50km) is just under 1% of Earth s radius. The exosphere is the uppermost layer of Earth s atmosphere.… …   Wikipedia

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  • Exosphere —    The farthest region of a planet s atmosphere. In this region particles can escape into space. The exosphere of Earth is about 400 km (249 miles) above the surface …   The writer's dictionary of science fiction, fantasy, horror and mythology

  • exosphere — egzosfera statusas T sritis ekologija ir aplinkotyra apibrėžtis Tarpinė zona tarp Žemės atmosferos ir tarpplanetinės erdvės – aukščiausias išorinis atmosferos sluoksnis, prasidedantis virš termosferos (vidutiniškai 600 km aukštyje). atitikmenys:… …   Ekologijos terminų aiškinamasis žodynas

  • exosphere — noun Etymology: International Scientific Vocabulary Date: 1949 the outer fringe region of the atmosphere of the earth or a celestial body (as a planet) • exospheric adjective …   New Collegiate Dictionary

  • exosphere — noun the uppermost layer of a planets atmosphere …   Wiktionary

  • exosphere — n. highest level of the atmosphere …   English contemporary dictionary

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