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As I mentioned in a \href{https://www.authorea.com/10997/}{previous post}, we now know that there There  is on average one planet orbiting every star in the Universe \citep{2013ApJ...764..105S, 2012Natur.481..167C}. If this comes as an exciting news, you might wanna have a look at the \href{https://www.authorea.com/10997/}{previous post}.  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. But how many of these planets are hosting life? And in particular,\textbf{ how many planets host intelligent life we might be able to communicate with}? In order to estimate the number of technological civilizations that might exist among the stars, in 1961 Frank Drake proposed the following simple equation