The Earth's thermosphere - consists of both the ionosphere and the exosphere, which feels cold because of the low density of air at that level. Measurements of air temperature reveal how energetic the measured particles are, but with fewer particles, the thermosphere is unable to effectively transfer heat. Heat may be transferred by direct contact between 2 surfaces; convection from one surface to another or by radiation. Energetic particles in the thermosphere to radiate heat, but the very low density of particles limit the amount of energy available to the zone as a whole, so the radiation remains relatively weak.
