The Rosetta mission to 67P/Churyumov–Gerasimenko is one of the pinnacles of modern scientific achievement. After a journey of millions of miles, it released its Philae lander which drilled into the surface and is producing fascinating data. One of its findings is that water on earth is unlikely to have come from comets, as scientists had speculated. Another is that there are organic molecules on the comet. Amino acids, the building blocks of proteins, may yet be found.

The mission – and renewed commitments to a manned mission to Mars – has sparked renewed interest in 'space theology'. What if there really is life on other planets? And does the sheer scale of the universe pose problems for believers? Christian Today spoke to Rev Prof David Wilkinson, a theoretical astrophysicist, Methodist minister and Principal of St John's College, Durham, and the author of Science, Religion and the Search for Extra-Terrestrial Intelligence (OUP).

On a scale of one to five, how excited are you by the Rosetta mission?

About a five. It's a 10 because of the technical achievement, which is astonishing. To land something on a body which is four kilometres wide and 6.4 billion kilometres away on a journey that takes 10 years – that inspires a thankfulness for the gift of science, and that we've been given the ability to do science.

The reservation that brings it down to five is that that I don't think the scientific discoveries are as significant as they've been hyped up to be. We've known for some time that amino acids – in some ways the building blocks of life – exist outside the earth. For instance, the Murchison meteorite that landed in 1969 in Australia – on that meteorite we saw amino acids. We know there are lots of organic molecules in the space betwen the stars in clouds of hydrogen which have organic molecules in them, and so it's not surprising if we see complex organic molecules.

What would really be exciting is if we began to see very simple life. The data needs to be processed, but actually they would probably need to have drilled deeper than they were technically able to do.

It is actually conceivable that there might be life on the comet?

That wouldn't surprise us, but at this point we need to be very careful, because when we talk about life, the imagination goes to intelligent life. It's a long way from an amoeba to an accountant. The Universe could be full of very simple life like amoebas and bacteria, but in fact what we're really interested in is intelligent life.

If the universe is full of very basic life, for me as a theologian, that is simply about God's extravagance, God's amazing energy and creativity which we see in the natural world around, to produce a tapestry of amazing life forms. But in a sense that's not a new theological problem. The question is, might there be somewhere where there is intelligent, self-conscious life and that will never happen unless you have planets. But the other dimension that is really hot in the news is that we're beginning to disover planets around distant stars, and I'm finding that more exciting than what we're finding out about comets.

If there are planets, could we ever know anything about them?

We've developed scientific techniques, not only looking for the radio signals that would be a giveaway for intelligent life – so that we might be able to watch their TV programs and listen to their radios – but observational techniques. The successor to the Hubble telescope, the James Webb, is going to be launched in 2017. That can look at planets we've already identified and tell us a little about their atmospheric composition. We could maybe even look for the kind of colours that might be a giveaway for life, for instance how much water there might be in liquid form. That's as well as looking for particular chemicals we know are associated with life, like ammonia, methane and carbon dioxide, and that will allow us to have a better sense scientifically even if we haven't been able to follow the model of the Interstellar movie and go and see these things.

How does the theology get more interesting if there is intelligent life?

The theological questions are about how special human beings are and how free God is to create. In 'Science, Religion and the Search for Extra-Terrestrial Intelligence' I argued that these two themes have been in tension in Christian theology. What's been really interesting is that Christians have been at the forefront of speculation about life on other worlds. There is a simple but powerful argument that says, if God is the sole creator of the universe, God can create life where he likes and how he likes without being constrained by our thinking. Then other Christians came along and said, might intelligent life on other planets undercut the special nature of human beings?

It was those who speculated about life on other planets who won out, and the reason is that, as historian of science Colin Russell pointed out, biblical Christianity defines the special nature of human beings not on the basis that we are at the centre of the universe or alone in the universe: it says we are special because of God's grace. He reaches out to us and forms a relationship with us not because we deserve it, but because he wants to do it. The Greeks associated status with place – in Aristotle's universe we were special because we are the centre of things – but biblical values said, it doesn't matter where we are, doesn't matter if we're alone or not, the thing that makes us special is the gift of relationship that God's given us.

Does this mean that God might have become incarnate on other worlds too?

Here the problem is much more pronounced, though to be honest very few have actually engaged with it. The physicist E A Milne, in the 20th century, talked about how for him the Jesus event was once for all, whether there was other life or not. Milne then said that Christians had to become cosmic missionaries, to take the gospel to all points of the universe. The difficulty in that is that it's such a long journey.

Other Christians said, maybe God becomes incarnate on other worlds – if there are little green women and little green men, maybe God becomes incarnate in little green flesh. The difficulty there, as CS Lewis pointed out in some of his science fiction, is that the incarnation is for two reasons. The first is to show us what God is like; Christians believe God was incarnate in Jesus to reveal his love for us. But the second reason is that Christians believe the incarnation was necessary for redemption and salvation. Lewis said, what if there is a civilisation that was intelligent, conscious of God, in relationship with God, but hadn't fallen? Would they need an incarnation? Personally, I haven't decided on whether there would be one incarnation or many. I just don't think we know enough. We can't be too dogmatic about this.

What would you say to someone who just found it impossible to believe in the signficance of tiny human beings in the vastness of the universe?

That's a question that goes right back to the Psalmist who wrote Psalm 8. There's a partial scientifc answer. That is to say, the universe is so old and so large – you need a universe of over 10 billion years old, and by implication on the Big Bang model that means a very big universe, in order to have the time in the interior of stars to cook the carbon that eventually forms my body.

However, you might say, couldn't the Lord have designed a quicker system to do that? So it may be that you say that human beings are not the only thing that God is interested in. The picture for me in Genesis is of God as the great artist. He throws the stars across the universe, he creates with extravagance and beauty, in a way that is not just about human beings, although we have a special part in this story. His concern is with beauty and wonder and creation for the fun of it. So it becomes a problem if you think that in the purposes of God human beings are the only product of the universe. There's a sense in which God the great artist has enjoyed himself in creation.

But it's a problem if you think about the universe only in scientific terms. Because the answer in Psalm 8, about human beings is, "But you created them, you made them, you gave them responsiblity. Human beings are only given significance by their relationship with God. Otherwise we are just a bit of fluff on the outskirts of a spiral arm in a not too unique galaxy somewhere on the outskirts of space and time. We're given significance because God in his grace has formed a relationship with us. The reason I believe in human significance is that I've seen God in Jesus showing us how special human beings are, by both becoming a human being and dying for me. That's what gives my life significance on a cosmic scale.