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The exosphere is almost a vacuum. Objects in the exosphere, like the Hubble Space Telescope (shown here), can be very hot when exposed to scorching sunlight or extremely cold when immersed in shadow.
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Image courtesy NASA.

Temperature in the Exosphere

The exosphere is very nearly a vacuum. The technical definition of the temperature of a gas (even a very thin one) is related to the average speed of particles (atoms and molecules). Since most of the particles in the exosphere are moving very fast, the temperature there is technically quite high. However, objects in the exosphere don't really "feel" much heat from the particles - there are simply too few gas particles, no matter how quickly they fly about, to transfer much heat to the objects they collide with. In general, the exosphere would feel very, very cold to us.

The temperature of most objects (like satellites) in the exosphere depends on whether they are lit by sunlight or are kept dark in shade. Objects lit by the intensely bright sunlight in the exosphere can become very, very hot. However, objects (or parts of objects) in shade tend to get very, very cold.

Last modified April 6, 2009 by Randy Russell.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF