thermosphere

A layer of the atmosphere located between the mesosphere and the exosphere. The fourth, counting from the bottom, of the five into which the atmosphere is divided, if we consider its vertical thermal structure. It extends from 80 to about 500-600 km of altitude, although its thickness is variable, sometimes being greater (thermopause). In this layer, air density is very low and it is strongly ionized, due to the action of ultraviolet radiation, gamma rays, and X-rays coming from the sun, which pass through it with barely any attenuation. The layer's name refers to heat (the prefix "thermo-" comes from the ancient Greek θερμός [ thermos ], meaning hot), since throughout it temperature increases with altitude, reaching very high values in its upper part, on the order of 1000-1500°C. During the day, as it is crossed by solar radiation, the rarefied gas making it up can reach considerably higher temperature peaks, of up to 2500°C, although any object located up there - as happens, for example, with the International Space Station - is not heated by contact, since the molecular density is so low that there is no heat conduction.