exosphere

== English == === Etymology === From exo- +‎ -sphere. === Pronunciation === === Noun === exosphere (plural exospheres) the uppermost layer of a planet's atmosphere 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', (Can we date this quote by Cassini Solstice Mission and provide title, author’s full name, and other details?), JPL, Mar. 02, 2012) ==== Derived terms ==== ==== Translations ====