The exosphere is the outermost layer of Earth's atmosphere, extending from about 500 kilometers to 10,000 kilometers above the surface. It is the least dense layer of the atmosphere and contains extremely low concentrations of gas molecules. The exosphere is where Earth's atmosphere transitions into outer space and is where satellites and other spacecraft orbit the planet. Research in the exosphere primarily focuses on understanding the composition, dynamics, and interactions of the gases and particles found in this region, as well as studying the effects of solar radiation and space weather on this part of the atmosphere.