This (in addition to cosmic radiation) is why we will probably not have bases on the surface of the moon. We’ll need some mass over our heads to survive.

Mare Tranquillitatis pit solves these problems. And there are likely many more caves that haven't been discovered yet.

https://en.wikipedia.org/wiki/Mare_Tranquillitatis_pit

Are what appear to be concentric wrinkles centered on the impact, artifacts of it? Like it was momentarily fluid and there are ripples on the surface of a lake.

Conchoidal fracture. The particle is probably a piece of obsidian or some other glass-like solid.

It is cool how many researchers around the world are still analyzing moon rocks from Apollo.