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%\item How common are planets?  %\item How common are planets similar to the Earth (Earth-like exoplanets)?  %\end{itemize}  The wealth of data provided by Kepler has revealed an astonishing fact: there is average one planet orbiting every star in the Universe \citep{2013ApJ...764..105S,2012Natur.481..167C}. Just in our Galaxy this means we have 100 billions planets. Since we have about 100 billion galaxies in the Universe, there are about 10,000,000,000,000,000,000,000 =$10^{22}$ planets out there. To put it in the words of W. Borucki, Principal Investigator of the KEPLER satellite: "When you wish upon a star, you are wishing upon a star with planets.    This is fascinating, but still it does not tell too much about the likelihood of extraterrestrial life. For example planests like Jupiter or Mercury are not expected to host life due to their extreme surfae conditions. But it could well be that this is the rule in the Universe and that Earth, with its mild average surface temperature was just a lucky shot of nature. Something that only happened, say, once.