deletions | additions       diff --git a/Intro.tex b/Intro.tex  index 3ce5a6c..93a78e9 100644  --- a/Intro.tex  +++ b/Intro.tex 
...
  This is fascinating, but still it does not tell much about the likelihood of extraterrestrial life. Planets like Jupiter or Mercury are not expected to host life due to their extreme surface conditions. This could well be the rule in the Universe, with Earth being just a lucky shot of nature. The question is then how common are planets that can likely support biological life.  A possible requirement is having a rocky planet in the so called Goldilocks or habitable zone, a range of distances from the host star where surface temperatures are just about right for liquid water to be present. This might well be a restrictive definition of habitability, as life forms might thrive in very different environments from what we are used to. But one has to start somewhere, and liquid water seems to have played a decisive role as a catalyst for biological life on Earth. \\  And here is where it gets very interesting, as just recently we learned that Earth-like planets are indeed very common. Statistically speaking 1 in 5 planets around Sun-like stars could potentially support life \cite{Petigura_Howard_Marcy_2013}. And Sun-like stars are extremely common, resulting in about 10 billion of habitable planets just in the Galaxy and Galaxy. Meaning that the  the closest to us could  potentially be  within 12 light years.\\ %$n_e \approx$ 0.2