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$N \approx f_l \times f_i \times f_c \times L$  The first interesting term to analyse is $f_l$. Given the presence of the right conditions, how likely is life to emerge?   The problem is that if life was impossible around stars noone would know it   Our it, and our  existence on Earth can not be used to draw conclusions on how probable is life in the Universe. Even if this probability was extremely low and life existed only on one planet in the Universe we would necessarily be on that planet. %Having one data point, the Earth, doesn't give any statistical information: the solar system could well be an extremely %unlikely, or even unique, place in the Universe. As soon as you ask the question "Are we alone?" it means you are alive %and conscious, i.e. you are in a sweet-spot, and you can not make any claim about how common that might be. Beside the fact that one such place exists.   The cool thing is that, statistically speaking, finding just another place where life can be supportedaround another star  changes everything. And this is where Even finding existing or fossil life on Mars or on one of the moons of Saturn or Jupiter would change completely the picture, as  it gets exciting. would demonstrate that the emergence of life (biogenesis) does not require a very specific environment.  Given %Given  what we know it could well be that the emergence of biological life was an incredibly fortuitous event that only happened %happened  once, here on Earth. But note that finding just another instance of life (existing or fossil) on another planet %planet  or satellite of our solar system would change completely the picture. That would demonstrate that life can easily %easily  emerge when the conditions are approximately right, and it does not require some very special conditions. That's why the exploration of Mars or the moons of Saturn/Jupiter are of paramount importance.