What is the Exosphere? - Definition, Facts & Temperature

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  • 0:00 Overview of the Exosphere
  • 0:15 Location
  • 1:50 Composition and Temperature
  • 2:42 Satellites
  • 3:20 Lesson Summary
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Lesson Transcript
Instructor: Katie Chamberlain

Katie has a PhD in Microbiology and has experience preparing online education content in Biology and Earth Science.

The exosphere is one of the layers of the Earth's atmosphere. Check out this lesson to learn the details that define it, such as location and composition.

Overview of the Exosphere

The Earth has five layers in its atmosphere: troposphere, stratosphere, mesosphere, thermosphere, and exosphere. The exosphere is like the icing on the Earth cake. It is the outermost layer.


Below the exosphere, closer to the Earth, is the thermosphere. Above the exosphere is the vast area of interplanetary space. Because the exosphere blends in with interplanetary space, some scientists even think it should not be considered a layer. Maybe someday it can hang out with the ex-planet, Pluto.

It is difficult to pinpoint the exosphere's exact distance from the Earth. The lower boundary where it meets the thermosphere is called the thermopause, or the exobase. This boundary can vary depending on the size of the thermosphere. During sun storms, the thermosphere tends to swell. As a result, the exosphere is further from the Earth. A ballpark estimate puts the lowest point of the exosphere around 500-1,000 km above the Earth's surface.

The outer limit of the exosphere is difficult to define as well. Sometimes the outermost area is defined as a place where hydrogen atoms can still be detected as a glow of scattered UV rays. This region is called the geocorona. The edge of the atmosphere can also be defined as the distance where the force of the Earth's gravity on a hydrogen atom becomes surpassed by the pressure from the sun's radiation. Don't worry if that is confusing. Just know that it is really really far, approximately 190,000 km away.

Composition and Temperature

The composition for the exosphere is much simpler than the rest of the atmosphere. This is because there really isn't any composition. It is practically empty, like a vacuum. There are often hundreds of miles between atoms and they rarely collide.

The temperature is difficult to measure in the exosphere because there are not many atoms. It would feel very cold to us because the air is so thin, but the few atoms up there are actually moving quite fast. They shoot around traveling and pop up from the lower and denser layers of the atmosphere. Sometimes they are just visiting before returning toward the Earth. Other times, they are on their way up and out into space. The Earth loses a bit of atmosphere every year.

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