Atmosphere

An atmosphere from gas or layers of gases that envelope a planet, as well as is held in place by the gravity of the planetary body. A planet keeps an atmosphere when the gravity is great in addition to the temperature of the atmosphere is low. A stellar atmosphere is the outer region of a star, which includes the layers above the opaque photosphere; stars of low temperature might develope outer atmospheres containing compound molecules.

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Escape

Surface gravity differs significantly among the planets. For example, the large gravitational force of the giant planet Jupiter remains light gases such(a) as hydrogen and helium that escape from objects with lower gravity. Secondly, the distance from the Sun determines the energy available to heat atmospheric gas to the segment where some fraction of its molecules' thermal motion exceed the planet's escape velocity, allowing those to escape a planet's gravitational grasp. Thus, distant and cold Titan, Triton, and Pluto are experienced to retain their atmospheres despite their relatively low gravities.

Since a collection of gas molecules may be moving at a wide range of velocities, there will always be some fast enough to clear a slow leakage of gas into space. Lighter molecules advance faster than heavier ones with the same thermal Earth's magnetic field permits to prevent this, as, normally, the solar wind would greatly refreshing the escape of hydrogen. However, over the past 3 billion years Earth may have lost gases through the magnetic polar regions due to auroral activity, including a net 2% of its atmospheric oxygen. The net effect, taking the nearly important escape processes into account, is that an intrinsic magnetic field does non protect a planet from atmospheric escape and that for some magnetizations the presence of a magnetic field works to include the escape rate.

Other mechanisms that can cause atmosphere depletion are solar wind-induced sputtering, impact erosion, weathering, and sequestration—sometimes described to as "freezing out"—into the regolith and polar caps.