Well the method doesn't really work for a game. If you load slot 1, then you have some planets. If you load slot 2 then you have some other random planets. But if you load slot 1 and play it and you have things like player health or items, then you load slot 2, you don't have this health or items it's a different game so it won't be continuous.
It is a complex game, especially if you want it in one layout. Even if you store planet co-ords in an array and spawn the planets again based on these, you also need to store what happens when you enter one of these planets and then load that data too.