I remember reading in an old Astronomy magazine (1978) about what it would take to terraform the Moon. There article said that the Moon could hold onto an atmosphere for a long time. It was either tens of thousands of years, or tens of millions of years- I don’t remember which. Anyway, what if the Moon had possessed an atmosphere briefly in its past? Liquid water flowing across its surface wouldn’t be out of the question.

I have two problems with the theory of water flowing on the Moon.

1. The Moon’s surface doesn’t show any evidence (I have not seen any) of water. There is evidence that liquid flowed on the Moon, but this liquid was lava.

2. The current theory of Moon formation say that it was very hot at the time of formation. All the volatiles were cooked out and blown away by the Solar Winds. Since then, comets have deposited volatiles on the Moon, but not in the quantities to create a temporary atmosphere.