The thermosphere is the hottest layer of the atmosphere. It extends from 80 kilometers above the surface of the Earth up to 600 kilometers and can heat up to 1,500 degrees Celsius because it’s very sensitive to solar activity. The air is thin and extremely hot, and there are sparse air molecules in this layer.
The sun’s energy heats the thermosphere. This layer receives large amounts of solar energy that increase its temperature. However, even if the temperature is incredibly hot, the air feels cold because the hot molecules are far apart from one another. A region called ionosphere lies within the thermosphere. In this region, the atmosphere’s sparse atoms and molecules are broken apart into ions and electrons (i.e. ionized) by solar radiation.