What Are the Characteristics of the Exosphere?

Since the exosphere is the topmost layer of Earth's atmosphere, the air in it is very thin as it slowly fades into outer space. The air in the exosphere has multiple similarities to the vacuum of space, and it is generally characterized by the existence of light atmospheric gases like helium and hydrogen alongside trace amounts of atomic oxygen and carbon dioxide.

Most satellites, including the International Space Station, orbit immediately below or within the exosphere. The exosphere is also the layer where molecules and atoms escape into deep space. The immediate layer before the exosphere is the thermosphere and the boundary that separates the two is known as the thermopause, which is about 375 miles above Earth. Atoms and molecules of atmospheric gases below the exosphere are often in constant collision with each other, but the molecules within the exosphere rarely collide because they are usually hundreds of miles apart. However, despite the huge distance between molecules, the exosphere experiences high temperatures because the molecules within it move at very high velocities.

The only part of the exosphere that is visible from Earth is known as the geocorona. Hydrogen atoms scattered within the geocorona cause it to have a faint glow of radiation.