Attacking a planet where you already have tokens would ordinarily make no sense, but I saw a player forced to do so recently because they already had tokens on all 4 planets (the 5th had earlier been blown up).
We did not see anything specifically prohibiting this in the rules, and we looked a little online, but could find nothing. So we decided that the player must choose a planet to attack, and if the defending player had no tokens there then the defender would have to defend with zero tokens, as usual. Winning obviously didn't help the player on offense, but the attack had to happen.
Is this the correct interpretation of the rules, or is a redraw of the destiny pile permitted in situations like this?
In this particular scenario, the player who was forced to attack under these unfavorable circumstances likely would have won if not forced to attack a system where gaining a base was impossible.