Also, made of green cheese. That implies alien space rats and I do not want to think of the consequences.

Joke aside, the moon has been known to 'ring like a bell' seismically which implies a rigidity to its mass but also suggests hollowness. I wonder how the moon's mass compares to its density and the density to that of solid rock. If the average density is lower, that implies hollowness.

Also, made of green cheese. That implies alien space rats and I do not want to think of the consequences.