If some of the other heavenly bodies are inhabited by human beings, God has not deemed it opportune to reveal this fact to us. Some say, if perhaps there are others inhabited, then these human beings are either in the purely natural state, or there was no case of original sin among them, or if there was, then they were regenerated in some other way than by the Incarnation. There is nothing intrinsically repugnant in all these views. It is difficult to say, however, whether these opinions can be reconciled with the free decree of the Incarnation in its relation to the human race. For revelation speaks of the human race as it exists on this earth.
Whatever is the fact about these gratuitous hypotheses, Christ, as the incarnate Word of God, is the culmination of the whole of creation, and, just as He is the head of the angels, at least as regards accidental grace, so He could be such with reference to human beings who might be living on some of the other heavenly bodies. Concerning these things and many others, we have no knowledge, and there is no need for them to trouble our faith. Some men seem to be of the opinion that on other heavenly bodies perhaps there are rational animals of another species than man. This position, while not verified, should not be rejected as contrary to the Christian faith.
In relation to this, we quickly examine the issue of “space” and our place in it. It must be noted that even if the world were the mathematical center of the universe, this would be no reason why God should choose it for the Incarnation. Thus Christ was not born in Jerusalem, but in Bethlehem. So also St. Augustine was the greatest theologian of his time, and yet he came into the world and taught not at Rome, which was the center of the world, but in Africa.
The mathematical position of a body is a matter of less importance with reference to a supernatural mystery, which infinitely transcends the spatial order. Likewise the possibility of life elsewhere. If we but found bacteria on Mars, we would have our “alien life.” What in this is contrary to the faith? Even those that hold a “literal creation” view cannot and should not hold that Genesis, in speaking of the creation of Earth, thereby rejects the creation of the other planets (it does not mention Mars but no creationist denies that Mars exists or is “unBiblical”) and also possible life on them.