The exosphere is almost a vacuum. This picture shows the Hubble
Space Telescope orbiting Earth in the exosphere. Places that are
lit by sunlight are very hot. Places in the shade are very cold.
Click on image for full size Image courtesy NASA. Temperature in
the Exosphere The exosphere is almost a vacuum. The "air" is
very, very thin there. When air is thin, it doesn't transfer
much heat to objects in the air, even if the air is very, very
hot. One definition scientists use for temperature is the
average speed of the molecules or atoms in a gas. When the
particles are moving very fast, the temperature is hot. When
particles are bouncing around more slowly, the temperature is
cooler. The particles in the exosphere are moving very quickly,
so the temperature there is quite hot. However, the exosphere
would feel quite cold to us. How can that be? Since the "air" is
so thin in the exosphere - it is almost a vacuum - there are
very, very few particles. We feel warmth when particles hit our
skin and transfer heat e