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see atmosphereatmosphere
[Gr.,=sphere of air], the mixture of gases surrounding a celestial body with sufficient gravity to maintain it. Although some details about the atmospheres of other planets and satellites are known, only the earth's atmosphere has been well studied, the science of
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(eks -ŏ-sfeer) See atmospheric layers.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



the outer and most rarefied layer of the atmosphere, where the mean free path of the particles is so large that they can be dispersed (diffused) into interplanetary space. The mass of the “air” in the exosphere is close to 10–10 times the mass of the atmosphere. Light gases, such as H and He, are the most quickly dispersed.

The exosphere begins at altitudes of 450 to 800 km, and its upper boundary is several thousand km above the earth’s surface, where the concentration of particles is the same as in interplanetary space. The exosphere consists of ionized gases (plasma), and the ratio of charged particles to neutral particles is close to unity where it begins; in the upper half of the exosphere, the air is almost completely ionized. The lower and middle parts of the exosphere are composed mainly of O and N atoms; with increasing altitude, the relative concentration of light gases, especially ionized hydrogen, grows rapidly. The gas kinetic temperature of the exosphere, which increases somewhat with altitude, is 1500° to 3000° K. An increase in solar activity warms the exosphere and increases its thickness. The magnetic field of the earth, which has an intensity of 0.3 oersted in the lower part of the exosphere and 10–2 to 10–3 oersted at its upper boundary, strongly affects the physical processes within it. The radiation belts of the earth are located for the most part in the exosphere.


Khvostikov, I. A. Fizika ozonosfery i ionosfery. Moscow, 1963.
Risbeth, H., and O. K. Garriott. Vvedenie v fiziku ionosfery. Leningrad, 1975. (Translated from English.)
Akasofu, S. I., and S. Chapmen. Solnechno-zemnaia fizika, part 1. Moscow, 1974. (Translated from English.)


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


An outermost region of the atmosphere, estimated at 300-600 miles (500-1000 kilometers), where the density is so low that the mean free path of particles depends upon their direction with respect to the local vertical, being greatest for upward-traveling particles. Also known as region of escape.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


exosphereclick for a larger image
The upper part of the thermosphere. It is the topmost part of the atmosphere and is approximately 300 to 600 miles (500–1000 km) above the earth's surface. In this region, the atmosphere is extremely tenuous because of high temperature and low density; some of the atoms and molecules escape the earth's gravitational field.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved
References in periodicals archive ?
The results, which provide new evidence about the origin of the lunar exosphere, are consistent with the idea that solar photon-driven processes dominate in supplying exosphere components.
Above starts the exosphere, where the atmosphere (mostly consisting of hydrogen atoms) thins out and merges with interplanetary space.
EXOSPHERE could bid to atone for his Royal Ascot flop in Thursday's Princess of Wales's at Newmarket.
NEWSBOY'S 1-2-3 1 EXOSPHERE 2 DARTMOUTH 3 BEAUTIFUL ROMANCE EXOSPHERE looks exactly the right type to give Sir Michael Stoute an incredible 10th Hardwicke Stakes victory.
The Queen's Dartmouth made all under Ryan Moore in the Ormonde Stakes last time and is another who would be inconvenienced if the race is tactical, but it is perhaps significant that Moore prefers Sir Michael Stoute's Exosphere, who is considered a big danger, this afternoon.
Sir Michael Stoute holds the answers to the Hardwicke Stakes (3.40pm) with Exosphere and Dartmouth both holding big chances of enhancing their trainer's superb record in the race.
Transits also help us understand more about the planet's exosphere which is the thin layer of gases that makes up its atmosphere.
Exosphere (17-2) continued Sir Michael Stoute's excellent run in the Group 2 Jockey Club Stakes.
AYR: 1.25 Shawaahid, 2.00 Priceless, 2.35 Foxtrot Romeo, 3.10 Exosphere, 3.45 GOLDEN STEPS (NAP), 4.20 Finn Class, 4.55 Steel Train, 5.30 Entihaa.
"From a technical perspective, the Grainster Exosphere is one of the largest cloud-based, custom application development projects of all-time."