What is the meaning of the exosphere


The Exosphere (from Greek έξο éxo 'Outside, outside' and σφαίρα sphaĩra 'Sphere') represents the outermost layer of the earth's atmosphere. It marks the smooth transition to interplanetary space, but according to the definition of NASA and the Fédération Aéronautique Internationale it is already part of it.

It is part of the heterosphere, i.e. that area of ​​the atmosphere from an altitude of approx. 120 km in which the gases separate and stratify according to their atomic mass. From an altitude of 1000 km only more hydrogen occurs than the lightest gas, this area becomes Geocorona called.[1]

The exosphere connects to the thermosphere and begins (according to various sources) at an altitude between 400 and 1,000 km. Its outer limit is given as around 10,000 km. However, the limit is not precisely defined because the gas density decreases continuously and theoretically never reaches the value zero. All the particles it contains are largely ionized. The exosphere is the only layer of the atmosphere from which gas molecules can leave the earth's gravitational field due to their own speed, as there are so few particles that their braking effect can be neglected. The exosphere is therefore also called Dissipation sphere designated.

The high temperature of over 1000 ° C, which apparently prevails in the exosphere, only relates to the speed of the particles (fast particles correspond to high temperatures). A thermometer would show temperatures below 0 ° C, as the gas density at this altitude is far too low to cause a measurable heat transfer.

Other planets or moons also have an exosphere, for example the planet Mercury, but also the Earth's moon.


  1. ↑ Geokorona at Wissen.de

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