The exosphere is the transition layer between the atmosphere and outer space, from ~600 km to ~10,000 km. Particle density is so low that the mean free path (distance between collisions) exceeds the layer's own scale.
The lightest particles (hydrogen, helium) can reach escape velocity and be lost to space (atmospheric escape). This process explains why Earth has lost most of its original hydrogen. Many geostationary satellites (36,000 km) technically orbit in the exosphere. It has no direct impact on surface weather.