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Matteo Cantiello deleted file Parameters.tex
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\section*{Updating the Drake equation}
$R$, the \textbf{rate of star formation}, tells how many stars are born every year in our Galaxy. This number is about 10 and might seem quite small, but the Galaxy is about 10 billion years old, so plenty of stars have born (and died) in the meanwhile. So $R\approx 10$. It's interesting to note that in 1961, when Drake wrote his equation, this was the only factor known.
$f_p$ Represents the \textbf{average number of planets around a star}.
%We now know that, in average, there is one planet orbiting every star in the Universe. 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". So $f_p \approx$ 1
As we discussed this number is now known: in average, there is one planet orbiting every star in the Universe \citep{2013ApJ...764..105S,2012Natur.481..167C} which means $f_p \approx$ 1
$n_e$ Is the \textbf{fraction of Earth-like planets}.
As from last year we also know this factor! Earth-like planets are very common. Statistically speaking at least 1 in 5 planets around Sun-like stars could potentially support life \cite{Petigura_Howard_Marcy_2013}. $n_e \approx$ 0.2
So the product of the first 3 terms is now well established and is, using a conservative approximation, of order 1.
$N =\underbrace{\overbrace{R}^{\approx10} \times \overbrace{f_p}^{\approx 1} \times \overbrace{n_e}^{\approx 0.2}}_{\sim 1} \times \underbrace{f_l \times f_i \times f_c \times L}_{?}$
We can then simplify the Drake equation and re-write it in its "2014 form" as:
$N \approx f_l \times f_i \times f_c \times L$
