The exosphere (from the Greek ἔξω [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 is defined by NASA and the Fédération Aéronautique Internationale already its part.
The exosphere connects to the thermosphere and begins (according to various sources) at an altitude between 400 km and 1000 km. Its outer limit is given as around 10,000 km. However, the limit is not precisely defined because the gas density continuously decreases and theoretically never reaches zero. Recent studies speak of 630,000 km, which extends far beyond the lunar orbit.
The exosphere is part of the heterosphere , i.e. that area of the atmosphere from an altitude of approx. 120 km in which the gases segregate and stratify according to their atomic mass . From an altitude of 1000 km only hydrogen occurs as the lightest gas, this area is called the geocorona .
All particles contained in the exosphere 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 known as the dissipation sphere .
The high temperature of over 1000 ° C that prevails in the exosphere results from the speed of the particles (fast particles correspond to high temperatures). An ordinary thermometer would not show such high temperatures, however, because the gas density at this altitude is far too low to bring about a measurable heat transfer .
Exosphere with other celestial bodies
- Earth's atmosphere extends to the moon. Retrieved March 6, 2019 .