Why is the exosphere so hot?

The exosphere is extremely hot due to its proximity to the Sun and the high energy of the few particles present at that altitude. Although it has very low density, the particles in the exosphere can reach temperatures exceeding 1,000 degrees Celsius (1,832 degrees Fahrenheit) because they absorb solar radiation and have high kinetic energy. This temperature measurement can be misleading, though, since there are so few particles that heat transfer is minimal, making it feel cold to a spacecraft or satellite passing through.