Scientific American had a brief QnA recently with David Weintraub, author of Religions and Extraterrestrial Life:How will we deal with it?. I should probably get it out of the way that I now hate David, having never met him, for publishing a book that I have been planning to write; although if the statement that "the Eastern Orthodox Church, a branch of Roman Catholicism" is any indication of Weintraub's understanding of theology then I need not worry about the competition. Klingons aside (who we all know are saved by Kahless) it is an important issue. Scientist become increasingly convinced that we will discover alien life in the next few decades, or even years. Personally I think this would be one of the biggest boons to our understanding of God, the Universe, and Everything since Jesus. Of course, it has to be more than just "life." Bacteria on Mars will be exiting, but not theologically significant. For that, we need intelligence. What that intelligence might look like is anyone's, and everyone's, guess; but I doubt we are going to run into any of the bumpy-forehead human analogs with which science fiction is replete. Nor do I think that we are going to run into any intelligent cultures that lack a belief system of some kind.
So what is at stake? From a Christian perspective, the issue is largely one of original sin. Supposedly supported by Romans 6 and other passages, this is the idea that humanity is corrupted in the Fall of Adam and that his sin is transmitted, kind of like sickle cell anemia, from one generation to the next. Christ's work on the cross, by this model, removes the sin stain from the Adamic line for all who believe. The problem then is what do you do if you have an intelligent something that is not a child of Adam? No Father Adam, no work of Christ for you Mr. Martian. While the concept of original sin has been around for centuries in Christianity, there are lots of other ways of understanding Christ's work on the cross, and why humans needed it, with the broader Christian framework of faith. C.S. Lewis, in his Space Trilogy, puts for the idea of variously fallen and unfallen worlds, just one of possibility in the spectrum. In fact, a careful reading of the literature of the Abrahamic Faiths (Christianity, Judaism, and Islam) shows a belief in lots of other intelligences: angels, demons, djinn, etc. These intelligences have been worked into the cosmology of the respective faiths, and accepted. New origins, distant origins, for supra-terrestrial beings will give pause, but not a faith break interruption. As the article mentions, lots of faiths are going to have not the slightest problem with incorporating alien life into their framework, since alien life practically exists already. Anytime such a monumental cultural stress inducer occurs new ways of thinking, new faiths even, will result. Syncretism, as much as we might wish to avoid it, happens. One need not look much further than our own world and history to see that.
I think the bigger problem when (yes, I am of the 'when' camp) we meet an alien civilization is going to purely existential. Humanity has dealt with other intelligent beings in out past, the genetic and fossil records show that. We either out competed them, or we mated with them. When next we see an other mind looking back at us, its not going to be so easy. We are going to question everything. We will test our assumptions about the world we live in, possibly to the point of destruction. Our faith is going to help us, I think, work out the answers.