DW: Now among the estimated fifty billion planets in our Milky Way, there are certain to be some earth-like ones. Do you also expect there to be life out there?

Ralf Jaumann: That's a large number and we cannot envisage that we are the only ones, but it's very difficult to figure it out because we are talking about a lot of space in there and enormous time spans.

But you think there is life out there? I mean would we have a chance to recognise it? Would it look like us?

We don't know. No, I don't think so. Because we are the top of this. 99 percent of life on earth are plants and microbes. Not human beings. Human beings don't count for biomass.

Yeah, but they count for us and they count for intelligence. Would life out there be intelligent, do you think?

If there's enough time and the right conditions for evolution, I think yes, it could be.

And it's always based on carbon?

It's based on carbon, on hydrogen, on phosphor, on oxygen and a number of other elements.

And the difficulty will actually be to detect that life. We've heard about Gliese 581 which turned out not to be a planet in the end. So hard will it be to detect life?

A little bit harder than it is to detect the planets. Because the planets are just tiny changes in brightness we can detect, but in order to detect life we have to look into the atmospheres of the planets. We have to see the planets themselves, so we need much better equipment than we have now.

So that would actually be a signal in the light that is emitted by the star and kind of touches the planet?

It's a reflection of the atmosphere and the molecules in the atmosphere, so if we find oxygen in the atmosphere that's probably produced by photosynthesis

I understand. On our Facebook page we also discussed the possibilities of life out there. And most of our viewers also think that there is life out there. Selva Wright asked about the necessary conditions for life to emerge. What about water? Do you need that?

I think water is necessary because water is the medium which really brings molecules together which are the keystones of life. It's the background for the mobility in order to do this. And it's a molecule itself that's able to dissolve rocks. So I think we think we need water and we need the right temperatures so the water is liquid.

So it's not just ice. Frederick Nelson asked whether these worlds might be conquered one day. So what about communication?

I think it's far away. And most of the worlds we've discovered now, which are very close are obviously not populated by intelligent people. If we go further and further, the time to communicate would be longer and longer. And longer and longer means millions of years... so....

Too long to wait for an answer. That's very long. Thanks very much for the talk, Professor Ralf Jaumann.

(Interview: Ingolf Baur)