The exosphere is the farthest layer of the atmosphere. It lies on top of the thermosphere. The exosphere starts at about 1,000 km above the surface of the Earth, but we don’t know exactly where it ends because it fades into outer space.
Some scientists disagree on whether the exosphere is even a part of the Earth’s atmosphere or not. To be a part of the atmosphere, a layer must have air particles. The air particles in the exosphere are so far apart that it feels like outer space.
Satellites can orbit the Earth within the exosphere, and some orbit even lower in the thermosphere. According to NASA, “A satellite is a moon, planet, or machine that orbits a planet or star.” People have put machine satellites into orbit around the Earth to learn more about the planet and to support television and cellular communication.
Gas particles within the exosphere will move in a straight line until they gradually fall back to Earth. They do not collide with each other very often because there are so few of them. Sometimes, gas particles with a lot of energy will actually fly out of Earth’s atmosphere into space. This means that Earth’s atmosphere has a slow leak as these particles leave the atmosphere. It is so slow that it won’t affect us, but scientists are studying it to learn more about the atmospheres of other planets.