Excerpted from "Brother Astronomer: Adventures of a Vatican Scientist."

Speaking of alien life forms...it's one of those questions that we get asked over and over again, mostly by reporters or people who don't know us very well. The Weekly World News once ran a story headlined "Missionaries for Mars! Vatican Training Astro-Priests to Spread Gospel to Space Aliens!" And deep down, I suspect some people think that's what the Vatican Observatory is really all about.

It isn't.

But still, we get the questions. It's part of a natural connection, one might even say confusion, between the science of looking at distant stars and the philosophy of worrying about the unknown in its many guises. People think we're looking for philosophical answers with our telescopes. What we're actually doing is inspiring philosophical questions.

One crucial question will face Christianity if, or when, extraterrestrial intelligence is discovered. Would aliens need to have their own version of Jesus?

It has been posited that the discovery of life elsewhere in the universe would fundamentally change the way we humans think about ourselves. Maybe; but, to borrow an insight from the historian of science Stephen Dick, I suspect that change has already happened. I really don't think anyone who's aware of the science would be fundamentally changed by the discovery, because nearly everyone expects that it will happen eventually. Probably not in our lifetime; maybe not in the next millennium. But eventually.

Finding any sort of life off planet Earth, either bacteria or extraterrestrials, would pose no problem for religion. Stephen Dick has recently written an excellent popular book on the history of how people through the ages have viewed the possibility of extraterrestrials ("Life on Other Worlds", Cambridge University Press, 1998). He notes that most atheists seem to think discovering extraterrestrial life would be the death of religion; but, in fact, most religious people don't see it that way at all. Indeed, as it happens some of the most prominent scientists currently working on the question of life on Mars are also active churchgoers.

God created the whole universe. There's nothing that makes one place more special than another. Religious people have been able to think in these "cosmic" terms all along, and happily speculated about "other worlds" long before the science fiction crowd had adopted the concept.

But there is one crucial question that will face Christianity if, or when, extraterrestrial intelligence is discovered. That's the question about what the Incarnation means to other species. In other words, would aliens need to have their own version of Jesus?

Do aliens need to be saved? Depends if they are subject to "original sin" or not. The traditional theology of original sin, tracing it back to the origins of the human race, says absolutely nothing about other entities, either way. Once we find other intelligences, we'll be in a better position to expand that theology.

Assuming that original sin, the problem of evil, does face other intelligences, what role does Christian salvation play in their world?

St. Paul's hymns in Colossians 1 and Ephesians 1 make it clear that the resurrection of Christ applies to all creation (".everything in the heavens and everything on earth"). It is the definitive salvation event for the cosmos. Another bit of Biblical evidence is the opening of John's Gospel, who tells us that The Word (which is to say, the Incarnation of God) was present from the beginning; it is part and parcel of the woof and weave of the universe.

Just how this "Word" might be "spoken" to the rest of the intelligent universe, I don't know. But it will be in "words" (that is, events) appropriate to those beings. In any event, good extraterrestrials (ETs), just like good humans, do not need to know about Christ for salvation; that's the tradition of "baptism by desire."

The point there is that, even though the life of Jesus occurred at a specific space-time point, on a particular world line (to put it in general relativity terms), it also was an event that John's Gospel describes as occurring in the beginning-the one point that is simultaneous in all world lines, and so present in all time and in all space. Thus, there can only be one Incarnation-though various ET civilizations may or may not have experienced that Incarnation in the same way that Earth did.

In science we assume that the laws of physics (which we know so imperfectly yet!) are as true everywhere in the universe as they are in our puny little laboratories here on Earth. Likewise, the "laws" of philosophy or theology-that is to say, the essential truths themselves, not to be confused with the formulas our human languages use to try to express these truths-are the same, and true, everywhere.

One of the big advances that St. Aquinas made was to insist, countering other popular philosophers of the thirteenth century, that there was only one Truth-not one truth for religion, another for science. Truth is one, even though our ways of groping for that truth are manifold. So the formulas we use-mathematical, philosophical, or whatever-can be very different, but they all are trying to get to the same place ultimately.

We have no data about other, nonhuman civilizations. They may not even exist; or they may be plentiful. (To insist that "God could not have made other worlds" was declared a heresy back in the thirteenth century-so this even covers alternate or parallel universes!) ETs may not be aware of the idea of an Incarnation, or they may have their own experience of the matter. Their experience may be so alien from ours that even though they have experienced God in their own way, it's an experience that we will never be able to share, nor they share in our experience.

I would suspect, though, that any conscious entity would wonder about the same things we wonder about-origins, meaning, etc.-and, just as we can learn from other cultures here on Earth, I would hope we could learn from other ET cultures.

Inevitably, any interaction with an unfamiliar culture results in some sort of evangelization. I recall my days in the Peace Corps, when kids in rural Africa would start adopting American customs, like wearing blue jeans, just because the Peace Corps teacher at their school wore blue jeans-even when the teacher tried not to influence the students!

So the question of whether or not one should evangelize is really a moot point. Any aliens we find will learn and change from contact with us, just as we will learn and change from contact with them. It's inevitable. And they'll be evangelizing us, too.

If we came across an ET culture that insisted 2+2=5, then we'd have to assume that either what they meant by 5 is what we meant by 4, or that one of us was seriously in error! Obviously we'd want to explore the matter further. "Evangelization" is what I would call this "exploration." We would clearly want to tell ETs what we have learned; we also want to listen to them, to hear what they have learned.

But one thing I know personally I have learned from studying eastern religions is that they have shown me the unique things that other cultures might not have had.for instance, the sense of a universe that is good, a creation of God, worth studying and worth caring for, and that one can come closer to God by immersing one's self in this universe (rather than trying to reject the physical world).

To withhold from an ET civilization a part of us as fundamental to ourselves as our religions-plural-would be dishonest, and certainly it would show no respect for them as equals. The important message that every Christian missionary has carried to each culture is that all people are equal and all of them are heirs to the knowledge of God that has been given to us. Soldiers might conquer them, secular philosophers might treat them as less than human (or, worse, condescend to them as "noble savages"), but the missionary can only accept them as equals.

Frankly, if you think about it, any creatures on any other planets, subject to the same laws of chemistry and physics as us, made of the same kinds of atoms, with an awareness and will recognizably like ours, would be at the very least our cousins in the cosmos. They would be so similar to us in all the essentials that I don't think you'd even have the right to call them aliens.