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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.



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.)



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.


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.
References in periodicals archive ?
Using instruments aboard the Japanese lunar orbiter SELENE (also known as Kaguya), Takaaki Tanaka and his team from the Tokyo Institute of Technology, made the first spacecraft-based observations of the lunar exosphere when the Moon was inside Earth's magnetosphere.
This process, called impact vaporization, continually renews the gases in Mercury's exosphere as interplanetary dust and meteoroids rain down on the planet.
Exosphere has been hard at work with the social media platforms, but lacks the big name backers of some recent campaigns.
Range Troposphere Up to 18 km (11 mi) -50[degrees]C to 18[degrees]C Stratosphere 18 to 50 km (31 mi) -50[degrees]C to 0[degrees]C Mesosphere 50 to 85 km (53 mi) -90[degrees]C to 5[degrees]C Thermosphere 85 to 500 km (310 mi) -90[degrees]C to 1,500[degrees]C Exosphere 500 to 9,600 km >500[degrees]C (6,000 mi)
Freedom Grill Inc, a US-based company that designs innovative products and accessories for the tailgating, camping and outdoor activities markets, has completed a merger with Exosphere Aircraft Company (Pink Sheets: EXSA).
Data from the final flyby has revealed the first observations of ion emissions in Mercury's exosphere, or thin atmosphere; new information about the planet's magnetic substorms; and evidence of younger volcanic activity than previously recorded.
He added: "My dad believed in human ingenuity and he believed in mankind's destiny beyond the exosphere.
They further divide the thermosphere into the ionosphere and the exosphere.
The planet's envelope of gas is so thin that the molecules don't generally collide with each other but bounce repeatedly off the surface like rubber balls, forming what planetary scientists call an exosphere.
For further information, please contact: Exosphere Aircraft Company Email: EXSAinformation@Yahoo.
Godolphin's Australian handler John O'Shea continued his strong season by saddling Exosphere to land the Group 2 Run to the Rose Stakes after Magic Hurricane's victory in the Premier's Cup handicap.
The moon has just the barest wisp of an atmosphere, technically called an exosphere because it is so tenuous, which leaves it vulnerable to CME effects.