Is our moon's gravitational field strong enough to retain a gaseous envelope and is there a gas with a sufficiently high molecular weight that could be used to create an 'atmosphere' for our moon?

Asked by: David Kronick

Answer

Our moon has what is called a transient atmosphere. There is gas on the moon but it is in such a small quantity that it really doesn't even count as an atmosphere. As to your question, their is no gas that can provide a permanent atmosphere to the moon.

Imagine the moon had an atmosphere similar to Earth's. The sun would heat up the air molecules giving them more kinetic energy This would cause them to move faster, and faster until eventually they would reach escape velocity and leave the planet. The moon's escape velocity is very small, and thus even a small amount of energy will make gas on the moon escape from its gravity.

Even the earth is constantly bleeding gas out into space, we just replenish our air supply through biological processes, and the occasional asteroid impact that brings in new gases.
Answered by: Mike Perkins, Physics/Astronomy Major, Penn State