The outermost region of a planet's atmosphere.
- ‘From the bottom of the exosphere the atmosphere has a thickness of 400 km.’
- ‘With around three hundred plus kilometers to go, we'll be in the exosphere, aka space, in no time at all.’
- ‘Since collisions are negligible above the exobase, the molecules in this region, called the exosphere, move along ballistic trajectories under the action of the earth's gravitational field.’
- ‘The anti-grav lifted the shuttle up into the exosphere, and then, after obtaining permission from Perimeter Traffic Control, the engines kicked in.’
- ‘Then more indicators flashed to life as the ship skimmed the outer exosphere at Mach 27.’