Historical Rules · 1 April 2011
Rule 309.5
Official source text from the 1 April 2011 Rules release
The controller of a face-up plane card is the player designated as the planar controller. Normally, the planar controller is whoever the active player is. However, if the current planar controller would leave the game, instead the next player in turn order that wouldn't leave the game becomes the planar controller, then the old planar controller leaves the game. The new planar controller retains that designation until he or she leaves the game or a different player becomes the active player, whichever comes first.