Drake equation

The Drake equation is a well-known example of a model relating the number of detectable extraterrestrial advanced civilizations in the galaxy to quantities with the potential for determination or some degree of estimation. Such a resulting number would be of interest to SETI (search for extraterrestrial intelligence). The equation was formulated by astronomer Frank Drake in 1961.

N = R* × fp × ne × fl × fi × fc × L

where:

• N - the resulting estimate of detectable extraterrestrial advanced civilizations.
• R_* - average rate of star formation in the galaxy.
• f_p - average fraction of those stars with planets.
• n_e - average number of life-supportable planets in such systems, i.e., in the habitable zone and so forth.
• f_l - fraction of those that actively develop life.
• f_i - fraction of those that develop intelligent life.
• f_c - fraction of those that develop technology that can release detectable signals.
• L - length of time for which such systems release detectable signals.