exosphere
/ˈɛksoʊsfɪr/
noun
- The outermost layer of Earth's atmosphere, where the air is extremely thin and gradually fades into outer space.
- The exosphere is the highest part of our atmosphere, starting about 500 kilometers above the Earth.
- Satellites in low Earth orbit travel just below the exosphere.
- In the exosphere, individual atoms can escape into space without colliding with each other.