The exosphere is the highest layer of the atmosphere. Together with the ionosphere, it makes up the thermosphere. The exosphere extends to 10,000 km above the Earth's surface. This is the upper limit of our atmosphere. The atmosphere here merges into space in the extremely thin air. Air atoms and molecules are constantly escaping to space from the exosphere. In this region of the atmosphere, hydrogen and helium are the prime components and are only present at extremely low densities. This is the area where many satellites orbit the Earth.