> if the ship falls into a heavier planet I would be a genuine paradox if this other planet appeared out of nowhere at some point in the process. That's the ke

> if the ship falls into a heavier planet I would be a genuine paradox if this other planet appeared out of nowhere at some point in the process. That's the key: both the source and the destination mass points have been there all along, and so you must, as usual, take into account all the bodies involved from the very beginning.