For more on what the future holds in this field of research, we talk to Professor Heike Rauer, a planetary researcher at the German Aerospace Center (DLR)
DW: There are 500 million habitable planets in our cosmic neighborhood. How long will it take till we discover life out there?
Heike Rauer: It will still take a bit because we don't really know if they are habitable. We think every second star out there has a planet, but we don't know yet if they have life.
Are you sure we will discover it some day? Is there anything like aliens or maybe just green slime? What do you expect?
I personally believe that life did not only form on earth and if there is life out there and it it a bit similar to earth, then we have a good chance of finding it.
Could you imagine anything else in a completely different form, from the type of life we have?
Life has to follow the biological and chemical principles, so it will probably be more or less like we find it on earth. And if it is very different - to be honest - we wouldn't find it, because we wouldn't know how to identify it.
What are the signals you are looking for to detect life?
If you wanted to detect modern life on earth you would look for oxygen. If you want to detect life on the early earth, where life formed, you would probably look for methane. So you are looking for key molecules which are very abundant in the atmosphere and that we can find in spectra of planets.
It is probably very interesting to find more and more exoplanets. But what are the real insights you can get for research - maybe also about our own solar system?
What we learned is, that other solar systems we discovered so far are very different from our solar system. We have for example a big gas planet like Jupiter but with an orbit of only a day around the sun - several thousand degrees hot. We have found planets ten times the mass of earth. What we have not found is a planetary system identical to the solar system and this is not because it is not out there. It is because technically the past missions and even the Kepler mission could not find it.
The earth is not exceptional?
The earth is probably not exceptional. But we still have the challenge to find a so-called second earth - a planet that is similar to earth. That is why we are planning new missions to follow Kepler.
Is there actually a chance to get Kepler back into operation?
No, they will use Kepler for other purposes but for planetary search unfortunately not. In Europe we are now planning a new mission to follow Kepler and complete the task.
Tell us more about it - how will you proceed?
What we want to do is follow the technique that Kepler uses, but have a much wider field of view, scan one million stars and find hundreds of small, earth-like planets. These planets will be around stars which are so bright that then for these stars we can look for these spectroscopic signals and see if they have an atmosphere and if they have life.
So we can hope?
Yes, we can hope.
What is the time schedule?
If we get these missions, we will find these planets in the next decade. But to find life on them will take a few more decades, I am afraid.