http://www.vaticanobservatory.va/co...--religion--society/faq-science-religion.html
Would the discovery of extraterrestrial intelligence – aliens – affect your faith?
The first and most important fact we have to confront in the whole question of “extraterrestrial intelligence” is this: we don’t know. Of all the planets we’ve found orbiting other stars, it’s not clear if any of them are suitable places for life as we know it. On none of them, nor indeed anywhere closer to us in our own Sun’s system of planets, have we ever found evidence that completely, uncontrovertibly, proves life originated in some place other that just here on Earth. As far as we know for sure, we could be alone.
Fr. Ernan McMullin, a philosophy professor at Notre Dame with a background in physics, has discussed the possible impact on Christian theology of discovering extraterrestrials, and he concludes only that it would certainly inspire theologians to develop new ways of thinking about topics like original sin, the immortality of the soul, and the meaning of Christ’s redemptive act. But, as he points out, there is already a voluminous literature, and hardly a consensus, on these points among theologians even today, without ETs!
Giuseppe Tanzella-Nitti, an astronomer and Opus Dei priest who teaches theology at the Pontifical University of the Holy Cross in Rome, comes to the same conclusion. He has written a lengthy entry on Extraterrestrial Life in the Dizionario Interdisciplinare di Scienza e Fede (The Interdisciplinary Dictionary of Science and Faith, of which he was an editor). But at the end, he concludes by saying (in my translation of his Italian), “the last word on the question of extraterrestrial life will not come from theology, but science. The existence of intelligent life on planets other than the Earth neither rules in, nor rules out, any theological principle. Theologians, like the rest of the human race, will just have to wait and see.”
The mere possibility of intelligent life elsewhere puts a human (or at least, human-like) face on the far better established astronomical observation of the enormity of our universe. For us Catholics, the thoughts that come from contemplating this question, in the absence of any firm answers, should lead us to focus on realizing God’s greatness and His special love for us.