[geoschmo]

If you put a starting point in a blank sector in the map editor it will create a planet. It will also create one if it can't find a suitable size and atmosphere, as in the case a lot of times if you do a good planet start, especially a multi planet start. But there are cases where it will use an exsisting planet. I'm just not sure of all the logic it goes through to make the decision.

There are also cases where it will change the atmosphere of an existing planet to use it as a homeworld. For example if you place a starting point in a sector that has a planet, but of the wrong atmosphere.