1) The outermost portion of the Earth's → atmosphere.
Extremely tenuous, it lies above the → ionosphere
from a height of about 500 km, to the edge of
→ interplanetary space.
Fr.: exosphère lunaire
An extremely thin gathering of gas surrounding the → Moon. It is made up of → atoms and → ions generated at the Moon's surface by interaction with → solar radiation, → plasma in the Earth's → magnetosphere, or → micrometeorites.