The exosphere is the outermost layer of Earth's atmosphere, situated above the thermosphere and extending to about 10,000 kilometers (6,200 miles) above the Earth's surface. In this region, the air is extremely thin, and particles are so sparse that they can travel hundreds of kilometers without colliding with one another. The exosphere is where low Earth orbit satellites and the International Space Station operate, and it gradually transitions into outer space. It primarily consists of hydrogen and helium, with trace amounts of other gases.