Mercuries Atmosphere

Mercury has only trace (very little) amount of the atmosphere it has. The atmosphere of Mercury is extremely thin; indeed, gas molecules in Mercury's atmosphere collide with the surface of the planet more frequently than they collide with each other; for most purposes Mercury can be considered to lack an atmosphere. The "atmosphere" is primarily composed of oxygen, potassium, and sodium.

The atoms that compose Mercury's atmosphere are continually being lost to space, with the average "lifespan" of a potassium or sodium atom being approximately 3 hours (during the Mercurian day—and only half that at perihelion). The lost atmosphere is continually replenished by several mechanisms; solar wind captured by the planetary magnetic field, vapor produced by micrometeor impacts, direct thermal evaporation of the polar ice, and/or outgassing.