exosphere Hear it!

exosphere definition

☆ exo·sphere (eks′ō sfir′, eks′ə-)

noun

the outermost portion of a planet's, esp. the earth's, atmosphere, consisting of a hot layer of light atoms often moving at escape velocity

Etymology: exo- + sphere

Webster's New World College Dictionary Copyright © 2009 by Wiley Publishing, Inc., Cleveland, Ohio.
Used by arrangement with John Wiley & Sons, Inc.

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