Is anybody out there – with a soul?

It is one of the deepest mysteries. Are we alone in the Universe? As we contemplate its majesty from our vantage point of a small, rocky planet circling an ordinary star in a backwater of our very average galaxy, we wonder if intelligent beings born under the light of a different sun also do the same.

Last week a team of US scientists from the University of California, Berkeley, reported in the journal Science that nearly one in four stars like the Sun could have Earth-sized planets capable of supporting alien life. And last month the UN made a little-known Malaysian astrophysicist head of its Office for Outer Space Affairs, to which is designated the task of talking to extraterrestrials if first contact is made. While the Royal Society held a two-day meeting to to work out a "scientific and societal agenda" on extraterrestrial life.

Yet despite this preparation and increasing evidence that other planets could, in theory, support alien life, we have barely searched the stars for it. We know radio signals can travel interstellar distances on little power. So we have used our radio telescopes, like the giant dish at Arecibo in Puerto Rico, to sift through the cosmic static in the hope of finding a signal that stands out as artificial. This way we have probed perhaps a few thousand stars out to a distance of about 100 light years (a light year is 6 million, million miles). So far we have found nothing, which is unsurprising as we do not know how much life there is out there, if any, and our galaxy has some 400 billion stars and stretches 100,000 light years. New dedicated arrays of radio telescopes are coming online to join the search that will enable us to probe deeper. Our cosmic quest is just beginning.

Theoretical physicist and cosmologist Stephen Hawking warned earlier this year that is it ok to search but "a little too risky" for mankind to beam our own messages into space as some have done, arguing that in the absence of any information about what's out there we should be careful. A few retort that we have already alerted local space to our presence because our TV and radio spills out among the stars. Others disagree: our leakage signals will be extraordinary difficult to detect and fade much sooner than was once thought. Best keep quiet.

But what happens if the search is successful and an astronomer picks up the artificial radio signal winking at us from some distant star? Initially we would probably have only very limited information about who sent it, and what they are like. But even so, the very existence of the signal would be profound, telling us one great truth that we are not alone, answering an age-old question and raising many more.

Some believe our civilisation will be shaken to the core by the news. Psychiatrist Carl Jung said that finding a far-more advanced civilisation would leave us "without dreams". Others have said that it will cause a fuss for a while and then, given the vast distance of space between us, it will fade and we will get on with things as normal. That may be the case for most of us, but there are some aspects of society that will never be the same.

We will have to do some readjustment to truly appreciate their alienness. They would be intelligent but without our human mentality. They could have power beyond our imagination, be immortal and almost omnipotent, transcending our history, our morals and our religions. They would not see the universe the way we do, and that would be fascinating to contemplate. As the American physicist Robert Oppenheimer said: "In another world the basic questions may have been asked differently."

When we find aliens, and if we are able to exchange information I would, at first, not be so interested in their scientific discoveries, as much as in what makes them different to us. How did they evolve? What do they look like? How do they organise their society? Do they have morals and a sense of right and wrong? Most of all, do they consider themselves to have souls? Do they have a God? Some religions have seriously considered the implications of finding intelligence in space, others have worked hard to avoid the issue altogether. The fact is it raises troubling questions that strike at the very foundations of some faiths, in particular Christianity.

Islam will welcome them. The Koran actually mentions life from outer space, and some Muslims have said it is the height of conceit to suppose that God created the vastness of the universe just for us to enjoy when we will never see the vast majority of it. Buddhists and Hindus with their philosophy of oneness and unity will have no problem accepting them as part of a cosmic brotherhood of consciousness.

It is Christianity that will find it hardest to adapt. There is a hard line of Christian thought that would deny aliens, however advanced, wise and serene they may appear to be, the same status as us. There is God and the angels, they say, who are spiritual beings without form, there are humans who have a soul and there are the animals. Aliens, because they are not human, are animals and therefore do not have the moral status we have.

Some scholars think aliens have souls. The Vatican astronomer Fr Guy Consolmagno believes they do: "Any entity – no matter how many tentacles it has – has a soul." He also adds that he, for one, would baptise an alien into the Catholic faith if they asked first, implying that once baptised they would be spiritually the same as humans as all souls are equal before God. Indeed, some say that if we found aliens, it would be the Church's duty to convert them, in the same way the Church travelled to the New World to save heathens.

The problem is that in Christian theology mankind and the Earth is privileged. Christians have a personal God and a personal relationship with Jesus. They believe that out of the immensity of space and time, God, the creator of everything, has singled out humans to be saved and has sent his son to redeem us. The question is, therefore, has God done the same for the aliens? Opinion is divided on this troublesome issue.

Padre José Gabriel Funes, director of the Vatican Observatory, said in 2008, "the extraterrestrial is my brother." He believes that in a cosmos with possibly billions of intelligent lifeforms, only humans have been saved and that God's son only came here, in a unique and unrepeatable event. Jesus did not suffer on other worlds. However knowledgeable the aliens may be and however seemingly good and wise they have become, they had not been visited by God's son, who did not die to redeem them. According to Fr Funes, for the aliens to have fellowship with God there will have to be another way. The Catholic commentator Joseph Breig wrote in 1960 that there can be only one incarnation, one mother of God, and only one race into which God has poured his image and likeness.

But from time to time a heretical thought emerges in this hesitant debate. Could God's son have visited other civilisations in space and redeemed them? In 1913 the poet Alice Meynell wondered in what guise the Christ trod the Pleiades, asking if there were a million gospels and a million forms of Jesus amongst the stars.

Whatever the theological status of aliens, the lesson from the cosmos is that we had better get used to being irretrievably lonely. We can search the length and breadth of time and space, search for almost an eternity if we wish, and we will never find another human. We could find remarkable lifeforms, philosopher-kings of space, creatures that have moved beyond the constraints of their biology, vast empires and incredible inventions. We could share in their accumulated wisdom and become demi-gods ourselves. But will we find men? No. Even in our miniscule corner of the cosmos there are far more stars than people.

One day we may converse with an alien. A future Pope and it may discuss questions of faith. But before that takes place, the search itself forces us to finally confront uncomfortable questions about our beliefs. If we are made "in the image and likeness of God", are creatures from the depths of space and who bear us no biological relationship, also made in his image?