Why does the Moon not have an atmosphere?
The Moon has no atmosphere worth mentioning because it did not have enough mass to keep an atmosphere from quickly escaping into space, and because it is geologically dead so the lost gases are not replenished. The Earth is much more massive than the Moon, so the Earth’s atmosphere leaks into space much more slowly. Also, the Earth is geologically and biologically active, which produces gases to make up for the gases lost to space.
