The Moon, or Luna, is a natural body that had been retrofitted into a space station. It is currently divided into a diplomatic zone, similar to how Antarctica is among our nations. There are groups of beings that are very unfriendly to eachother that are a few kilometers apart on the Moon that exist in peace as long as strict protocols are followed. The entire interior of the Moon has been built out by different ET races.
Our Moon was transported into our solar system hundreds of millions of years ago by another race. It was put into orbit around the Earth 64 million years ago. An energetic tether emanating from deep inside the Earth anchors the Moon in its near-perfect circular orbit. Its main purpose was to speed up evolution on Earth following the extinction of the dinosaurs.