You can open the English.str file located in the Strings folder in your Sins install path. It contains all the star/planet names, as well as ships, AI factions, and the like. The planet names should be towards the top of the file, and there are a lot of them!

Those'll be in your user path. Go to the options - mods - show mod path in the game, and in the SoaSE folder will be a folder for saves along with the mods.

Make sure you can see them by going to folder options - view - show hidden files/folders.