What does thermosphere mean?
The thermosphere is the region of Earth's atmosphere above the mesosphere, beginning at roughly 85 kilometres above the surface and continuing outward for several hundred kilometres. It is notable for temperatures that generally rise with altitude, unlike the cooler layers below it. This counterintuitive increase occurs because the sparse gases there absorb highly energetic ultraviolet and X-ray radiation from the Sun. The thermosphere also overlaps with the ionosphere, where solar radiation produces charged particles, and is the region in which many low-orbit satellites travel. References to the thermosphere therefore combine ideas from atmospheric science, spaceflight, auroral physics, and the study of the upper atmosphere. Its name reflects its thermal environment and spherical form. Although sometimes used loosely as a synonym for the upper atmosphere, the word has a more precise meaning: a distinct atmospheric layer distinguished by its altitude, rising temperatures, and ionized particles.
nounThe region of Earth's atmosphere above the mesosphere, beginning at an altitude of roughly 85 kilometres and extending to about 500–1,000 kilometres. Temperatures in this layer generally increase with altitude, and energetic ultraviolet and X-ray radiation produces ions and excited atmospheric particles.
- The thermosphere is the outer region of an atmosphere, especially Earth's, lying above the mesosphere and overlapping with much of the ionosphere.
"Satellites in low Earth orbit pass through the thermosphere, where temperatures can rise dramatically with altitude."
"The thermosphere extends hundreds of kilometres above the surface of the planet."
"Auroras occur mainly in the thermosphere, where energetic particles collide with ions and excited gases."
Used when referring to the thermospheres of multiple planets or atmospheric bodies.
"The thermospheres of Earth and Mars both interact with the solar wind."
The thermosphere gets hotter as you climb: its sparse gases absorb intense solar radiation, turning the layers farthest from the Sun into the atmosphere's hottest region.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does thermosphere come from?
Thermosphere was formed in modern scientific usage by combining thermo-, from Greek thermē meaning “heat,” with sphere, from Greek sphaira meaning “sphere.” The compound follows established English patterns seen in related words such as thermal and thermometer. Its sphere element belongs to the same Greek-derived family as atmosphere and hemisphere, words ultimately based on sphaira.
Related word forms
How thermosphere is actually used
The term is primarily scientific and educational. In discussions of Earth, it is also sometimes used informally to mean the upper atmosphere generally, although the thermosphere is a specific layer.
Easily confused with thermosphere
The stratosphere is the atmospheric layer below the mesosphere and thermosphere, extending roughly from 12 to 50 kilometres above Earth's surface.