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Exosphere facts for kids

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EarthAtmosphereBig
Diagram showing the five primary layers of the Earth's atmosphere: exosphere, thermosphere, mesosphere, stratosphere, and troposphere. The layers are to scale. From the Earth's surface to the top of the stratosphere (50km) is just under 1% of Earth's radius.

The exosphere is the highest and top layer of the Earth's atmosphere. It marks the edge of space.

There are very few molecules in this layer. The lightest atmospheric gases such as hydrogen and helium exist throughout the exosphere. Heavier ones like carbon dioxide and atomic oxygen are near the base.

The molecules collide so rarely, that the idea of atmospheric pressure has little meaning.

There are two borders to the exosphere; the lower boundary and the upper boundary. The lower boundary is about 500-800 km (300-500 miles) above the surface and is called the exobase. It is also called the thermopause because it is in between the exosphere and the thermosphere. The molecules are moving very fast, so the temperature in this zone is estimated to be between 0-1700 degrees Celsius.

The upper boundary of the exosphere starts at the distance where the influence of solar radiation pressure on atomic hydrogen is hihger than that of Earth's gravitational pull. This happens at half the distance to the Moon or somewhere in the neighborhood of 200,000 kilometres (120,000 mi). The exosphere can be seen from space and is called the geocorona. It extends to at least 10,000 kilometres (6,200 mi) from Earth's surface.

See also

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