This thread will contain several follow up questions, but let me start with the most simple one. Imagine a planet with no atmosphere and a ball in empty space. The ball is dropped on the planet from a certain height and starts bouncing. We ignore friction and consider this to be the fully elastic case. Hence, if I am not mistaken, we are only concerned with energy and momentum conservation. We do _NOT_ ignore that the planet has a high mass compared to the ball, but nevertheless it is not infinite but finite. So my question is, will the ball keep bouncing forever and retain the same height, or will it eventually become "one", hence at rest with the planet, having transferred all it's momentum to the now planet+ball system as "one"?