Flexi Says: The exosphere is the layer above the thermosphere. This is the top of the atmosphere. The exosphere has no real upper limit; it just gradually merges with outer space. Gas molecules are very far apart in this layer, but they are really hot. The exact temperature varies with solar activity, from around 700 K (about 427°C) during minimum sunspot activity to 1400 K (about 1127°C) at maximum sunspot activity. However, because the actual particles of gas are very few and far apart, the amount of thermal energy in the exosphere is very low.
