Thermosphere

The thermosphere extends upwards to altitudes of several hundred kilometres, where temperatures range from 500 K to as high as 2,000 K (Kelvin), depending on the degree of solar activity. The temperatures between day and night vary by hundreds of degrees. The height of the thermopause varies from about 200 to 500 km, again depending on solar activity. Above 500 km temperatures are very difficult to define. Molecules are so widely spaced that they move independently, and there is no reason why their temperatures should be the same.