I can't remember exactly, but the moon (Kingu) was either left here from Nibiru when it collided with Tiamat, or it was moved from Mars and dropped here by Nibiru. It's in the Enuma Elish and the Tablets of Enki but I don't remember right now. And the moon was visited by Enki and Marduk at one point so there's no telling how many others visited it or decided to make it a base to watch us.