When Christianity spread throughout the West, the Ptolemaic system became very widely accepted, and although the Church never issued any formal pronouncement on the question of alien life at least tacitly, the idea was aberrant.
Bishop of Paris, Étienne Tempier, did overturn Aristotle on one point: God could have created more than one world (given His omnipotence). Taking a further step, and arguing that aliens actually existed, remained rare.
Notably, Cardinal Nicholas of Kues speculated about aliens on the Moon and Sun.
William Vorilong also speculated about the existence of humans on alien worlds, but he came to the conclusion that God, although empowered to create them, would choose to not do so.
image: Nuremberg broadsheet tells of an April 14, 1561, aerial battle involving a variety of strange objects — globes, crosses, and tubes — that turned to steam upon hitting the ground (lower right). People viewed the event as a divine warning.