• Exosphere

    Origin

    - + sphere + -

    Full definition of exosphere

    Noun

    exosphere

    (plural exospheres)
    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', Cassini Solstice Mission, JPL, Mar. 02, 2012)
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