The idea I had on how this works is that the entire planets in the space stage are pre-generated. So we can use a lot of computing time to finish simulating a planet for a wanted amount of time (or until an advanced enough species appears), then the planet can be saved and we can include that with the game files. That way we can have well generated (within all the game rules) planets in the space stage, without it taking a really long time to generate when playing the game.