The search for life in the universe is one of the most challenging topics of science. It is not a modern topic at all, since more than 100 years ago, it was speculated that on the Moon, there are oceans and seas; on Venus, there are swamps and also Mars is inhabitated. However, now we have the scienti'c background and the scienti'c tools to answer this question and it is also certain that the answer would have deep imp- cations for our culture, philosophy,...