exosphere

noun

exo·​sphere ˈek-sō-ˌsfir 

: the outer fringe region of the atmosphere of the earth or a celestial body (such as a planet)

exospheric

ˌek-sō-ˈsfir-ik  -ˈsfer- 

adjective

Examples of exosphere in a Sentence

Recent Examples on the Web

The next step is to try and figure out what the composition of the exosphere is, a task ideally suited to the James Webb Space Telescope. — Keith Cooper, Space.com, 5 May 2026

Its thin exosphere offers almost no protection from solar radiation, making this twilight boundary a literal knife-edge of danger. — Kaif Shaikh, Interesting Engineering, 13 Nov. 2025

Orbits of the Earth ultimately decay, as faint traces of the exosphere produce drag, causing a circling object eventually to plunge into the atmosphere and incinerate. — Jeffrey Kluger, Time, 14 Nov. 2025

The Sphere partnership will once again see AMC branding (and partner branding) on the Sphere’s exosphere around Halloween, and this year around the holidays as well. — Alex Weprin, HollywoodReporter, 3 Sep. 2019

Word History

Etymology

exo- + -sphere

First Known Use

1949, in the meaning defined above

Rhymes for exosphere

• atmosphere
• biosphere
• centromere
• chemosphere
• chromosphere
• hemisphere
• hydrosphere
• lithosphere
• mesosphere
• microsphere
• miserere
• mountaineer

Kids Definition

exosphere

noun

exo·​sphere ˈek-sō-ˌsfi(ə)r 

: the outermost region of the atmosphere of the earth or a planet