This layer is most effected by the solar wind. Solar wind is stream of charged particles from the Sun. The Earth's magnetic field diverts most of the particles but not all. Some get trapped in belts of radiation called the Van Allen Belts . Others follow the lines of the Earth's magnetic field to the north and south poles.
Some planets only have an exosphere.
The Space Shuttle, some communications satellites, etc. The drag from this small amount of atmosphere effects the orbits. Different answers for terrestrial and gas planets. Most important source of atmosphere is outgassing by volcanic eruptions. Eruptions release trapped gas below crust.