Good catch. We probably shouldn't have displayed that particular metric (planets lost) since there's no reasonable way for players to save planets. Or it should have been phrased more positively (You're doing awesome, look how many disasters you survived / avoided!).
Technically, if a planet doesn't go into the black hole, it doesn't count against your "planets lost" score. So an extremely dedicated player could try flinging objects at planets to knock them off course. But that'd be a difficult way to play, because you'd be sacrificing your own safety.