The Drake Equation
The probability of life on other planets is a question that has stifled humans since our existence. Whether or not conditions are right somewhere on an extra solar planet for another civilization such as ours to flourish we don't know. All we can to is make assumptions and hypotheses. In 1961 Frank Drake tried to figure out the probability of life on other planets by using a formula, the Drake Equation. N=R*fp*ne*fl*fi*fc*L This equation may seem very difficult to decipher but only consists to plugging in variables.
N = The number of communicative civilizations
The number of civilizations in the Milky Way Galaxy whose radio emissions are
detectable.
R* = The rate
of formation of suitable stars
The rate of formation of stars with a large enough "habitable zone"
and long enough lifetime to be suitable for the development of intelligent life.
fp = The
fraction of those stars with planets
The fraction of Sun-like stars with planets is currently unknown, but evidence
indicates that planetary systems may be common for stars like the Sun.
ne = The
number of "earths" per planetary system
All stars have a habitable zone where a planet would be able to maintain a
temperature that would allow liquid water. A planet in the habitable zone could
have the basic conditions for life as we know it.
fl = The
fraction of those planets where life develops
Although a planet orbits in the habitable zone of a suitable star, other factors
are necessary for life to arise. Thus, only a fraction of suitable planets will
actually develop life.
fi = The
fraction life sites where intelligence develops
Life on Earth began over 3.5 billion years ago. Intelligence took a long time to
develop. On other life-bearing planets it may happen faster, it may take longer,
or it may not develop at all.
fc = The
fraction of planets where technology develops
The fraction of planets with intelligent life that develop technological
civilizations, i.e., technology that releases detectable signs of their
existence into space.
L = The "Lifetime" of communicating
civilizations
The length of time such civilizations release detectable signals into space.
It is only recently that extra solar planets have been discovered. It is possible they have life on them; only time and science will tell.
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N=R*fs*fp*ne*fl*fi*fc*L