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.