exosphere
nounUK /ˈɛksəʊsfɪə/ · US /ˈɛksoʊsfɪɚ/
Etymology From exo- + -sphere.
1
the uppermost layer of a planet's atmosphere
2
an extremely thin atmosphere, as on Saturn's moon Dione
- "Scientists weren't even sure Dione would be big enough to hang on to an exosphere" ('Cassini Detects Hint of Fresh Air at Dione', , JPL, Mar. 02, 2012)
- Derived terms
- exospheric