exosphere

The exosphere is the outermost layer of Earth's atmosphere, where particles are so spread out that they can drift into space. It begins about 600 kilometers above the surface and extends thousands of kilometers outward. In this region, atoms and molecules, mainly hydrogen and helium, move very slowly and may escape into space. The exosphere acts as a transition zone between our atmosphere and the vacuum of space, playing a key role in how our planet interacts with the universe. Because of its thinness, it contains very few particles, making it quite different from lower atmospheric layers.