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1. The outermost region of a planet's atmosphere.
2. The outermost region of the earth's atmosphere, lying above the thermosphere and extending thousands of kilometers into space, from which molecules having sufficient velocity can escape the earth's gravitation.
ex′o·spher′ic (-sfîr′ĭk, -sfĕr′-) adj.
(Physical Geography) the outermost layer of the earth's atmosphere. It extends from about 400 km above the earth's surface
the highest region of the atmosphere.
ex`o•spher′ic (-ˈsfɛr ɪk, -ˈsfɪər-) adj.
The outermost region of the Earth's atmosphere, lying beyond the ionosphere and extending indefinitely into space. The air in the exosphere gets thinner and thinner until the lightest particles, such as hydrogen atoms, begin to escape Earth's gravity.
the highest portion of the earth’s atmosphere, from which air molecules can escape into space. Cf. ionosphere.See also: Atmosphere
The outermost layer of the atmosphere of a planet.