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Word of the Day Wednesday, June 10, 2026

exosphere

/ɛksəˈsfɪər/ noun · British & US
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What does exosphere mean?

noun

The outermost layer of a planet's atmosphere, extending from the thermosphere to the interplanetary space. It is a very thin layer of gas that surrounds a planet.

Example

"The exosphere of Mars is thought to be composed mostly of carbon dioxide and noble gases."

Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.

Etymologically related

Synonyms for exosphere

Rhymes with exosphere