So... what would happen if you destroyed ALL the planets, then tried to rebuild one?
Early Versions of the game (maybe just beta Versions) allowed for no-atmosphere gas giants but the community soon noticed how silly that was ("Sir! We have detected a large mass!" "Onscreen! ... umm... there's nothing there, Lieutenant!" "Yes sir, but according to stellar cartography there's SUPPOSED to be a planet around here SOMEWHERE!"
)