Exosphere
Exosphere
Exosphere (pronounced: ex-o-sphere) is the outermost layer of the Earth's atmosphere. It starts at an altitude of about 700 km above the Earth and goes up to 10,000 km. The exosphere is primarily composed of extremely low densities of hydrogen, helium and several heavier molecules including nitrogen, oxygen and carbon dioxide closer to the exobase.
Etymology
The term "Exosphere" comes from the Greek words "exo", meaning outside, and "sphaira", meaning sphere. It was first used in the context of Earth's atmosphere in the mid-20th century.
Characteristics
The exosphere is characterized by extremely low density and high temperature. It is the layer where atoms and molecules escape into space. This layer is often referred to as the "upper limit" of the atmosphere. The boundary of the exosphere and outer space is called the exobase or 'critical altitude'.
Related Terms
- Thermosphere: The layer of the Earth's atmosphere directly below the exosphere.
- Ionosphere: A region of the Earth's atmosphere that is ionized by solar radiation and is located within the thermosphere and exosphere.
- Exobase: The lower boundary of the exosphere.
- Atmosphere of Earth: The layer of gases, commonly known as air, that surrounds the Earth and is retained by Earth's gravity.
See Also
External links
- Medical encyclopedia article on Exosphere
- Wikipedia's article - Exosphere
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