The exosphere is a thin, atmosphere-like volume surrounding a planet or natural satellite where molecules are gravitationally bound to that body, but where the density is so low that the molecules are essentially collision-less. In the … See more

Mercury, Ceres and several large natural satellites, such as the Moon, Europa, and Ganymede, have exospheres without a denser atmosphere underneath, referred to as a surface boundary exosphere. Here, molecules are ejected on elliptic trajectories See more

The most common molecules within Earth's exosphere are those of the lightest atmospheric gases. Hydrogen is present throughout the exosphere, with some helium, carbon dioxide, and atomic oxygen near its base. Because it can be hard to define the … See more

• Aeronomy
• Extraterrestrial atmospheres
• Extraterrestrial skies
• List of natural satellites See more

If the atmosphere of a celestial body is very tenuous, like the atmosphere of the Moon or that of Mercury, the whole atmosphere is considered exosphere.
The Exosphere of Mercury
Many hypotheses exist about the formation of the … See more

• Prölss, Gerd W. (2012) [2004]. Physics of the Earth's Space Environment: An Introduction. Translated by Michael Keith Bird. Springer. See more