Ray Etherton, via Facebook asked:
Why does the moon have no atmosphere at all?
Ray from Rylstone Australia
We posed this question to Peter Braesicke from the University of Cambridge...
Peter - I think the Moon is just too small. There's not enough gravity there to keep an atmosphere and so, because the Earth is much, much bigger, it is able to keep the atmosphere gravitationally together and so, that's why we enjoy the benefit of the atmosphere.
yes, the mass of the moon is too small. The moon's gravity is too weak to keep gas or even liquid particles on its surface, due to ambient energy coming from the sun and from its core, in particular during its young age when it was very hot. The energy accelerates the particles to speeds beyond the escape velocity.
Actually, the moon does have an atmosphere. See this article from NASA. http://www.nasa.gov/mission_pages/LADEE/news/lunar-atmosphere.html#.VEnKaOeKv6o John Handshoe, Fri, 24th Oct 2014