Little green men might shock the secular public. But the Catholic Church would welcome them as brothers.

That's what Vatican chief astronomer and papal science adviser Gabriel Funes explained in a recent article in L'Osservatore Romano, the newsletter of the Vatican Observatory (translated here). His conclusion might surprise nonbelievers. After all, isn't this the same church that imprisoned Galileo for saying that the Earth revolves around the sun? Doesn't the Bible say that God created man – not little green men – in his image?

Indeed, many observers assert that aliens would be bad for believers. Jill Tarter, director of the Center for SETI Research, once wrote that finding intelligent other-worldly life "will be inconsistent with the existence of God or at least organized religions." But such predictions tend to come from outside Christianity. From within, theologians have debated the implications of alien contact for centuries. And if one already believes in angels, no great leap of faith is required to accept the possibility of other extraterrestrial intelligences.

Since God created the universe, theologians say, he would have created aliens, too. And far from being weakened by contact, Christianity would adapt. Its doctrines would be interpreted anew, the aliens greeted with open – and not necessarily Bible-bearing – arms.

"The main question is, 'Would religion survive this contact?'" said NASA chief historian Steven J. Dick, author of The Biological Universe. "Religion hasn't gone away after Copernican theory, after Darwin. They've found ways to adapt, and they'll find a way if this happens, too," Dick says.

The central conundrum posed to Christianity by alien contact would involve the Incarnation – the arrival of Jesus Christ as God's representative on Earth, his crucifixion and the absolution of humanity's sins through his forgiveness.

"It would still be true – but if there are other races and intelligences, then what is the meaning of this visit to our race at that time?" asked Vatican astronomer Guy Consolmagno, who in 2005 penned the booklet Intelligent Life in the Universe?

Some propose that the Earthly incarnation of Jesus some 2,000 years ago redeemed all intelligent creatures, in all places and – since a space-faring race is likely older than us – in all times. Others have suggested that Jesus could take multiple forms.

"Just as Jesus is human like you and I, you would find an alien-specific Jesus," said Pacific Lutheran Theological Seminary professor Ted Peters.

But Peters and others also say that aliens may not have fallen into sin, instead existing in a state of grace, neither having nor needing Jesus. In that case, missionaries would have no call to convert them.

"Would sin be the same on another planet as we conceive of it here? Would there even be sin, or would God be present to that species in a completely different way?" says Richard Randolph, a Kansas City University ethicist.

All this, however, assumes that humanity not only encounters new forms of life but also understands them. Other intelligences may be incomprehensible to us, thus intensifying another doctrinal question: What does it mean to be made, as the Bible proclaims, in God's image?

Many astrotheologians argue that God's image refers to our spiritual nature, with our physical forms being irrelevant. Not everyone, however, agrees.

"If there are aliens, the Bible specifically does not say that they were created in his image," said Mark Conn, pastor of the Noble Hill Baptist Church in Springfield, Missouri. "God created many other intelligent beings on this planet, and they were not created in His image."

Conn's church recently met to discuss the issues posed by extraterrestrial contact, ultimately deciding that "if they're there, they're there. It doesn't change a whole lot."

Unlike Peters, Conn suggested that missionary work may be required, something the aliens may not welcome – especially if, as many postulate, they are technologically superior to humanity and do not have religions of their own.

"Maybe they'll say that they used to need religion but have outgrown it. Some people say that would be a great blow to religion, because if an advanced civilization doesn't need it, why do we?" said Douglas Vakoch, director of interstellar message composition at SETI.

"I don't buy it, though. I think religion meets very human needs, and unless extraterrestrials can provide a replacement for it, I don't think religion is going to go away," he continued. "And if there are incredibly advanced civilizations with a belief in God, I don't think Richard Dawkins will start believing."