Thermosphere

The thermosphere is a warm layer above the mesosphere. In this layer, there is a significant temperature inversion. The few molecules that are present in the thermosphere receive extraordinary amounts of energy from the sun, causing the layer to warm. Though the measured temperature is very hot, if you exposed your skin to the thermosphere, the perceived temperature would be very cold. Because there are so few molecules present, there would not be enough molecules bombarding your body to transfer heat to your skin. Temperature is a measurement of the mean kinetic energy , or average speed of motion, of a molecule, so although there are only a few molecules, each has a huge amount of kinetic energy.

Above the thermosphere is the exosphere. Unlike the layers discussed previously, there is no well defined boundary between the thermosphere and the exosphere (i.e., there is no boundary layer called the thermopause).