Poor Mercury. Since its formation, Mercury has substantially shrunk. It gets hit by more meteors than any other planet in the Solar System, and its “atmosphere” is so thin it doesn’t even deserve the name. Scientists call it an exosphere instead.
What little air Mercury has comes from several sources. Volatile chemicals seep out of the planet’s crust through a process called outgassing. In addition, those meteor impacts kick up plenty of dust particles. Mercury even gets some spare hydrogen and helium from the Sun.
But the Sun giveth and the Sun taketh away. The constant pressure of solar radiation blows most of Mercury’s gaseous materials away.
Mercury’s gravity and weak magnetic field hold some of the planet’s exosphere in place, but not enough. Just another reason why nobody wants to live on Mercury.
Atmosphere of Mercury from Universe Today.
The Planet Mercury Has a Comet Like Tail from Watts Up With That?