The Drake Equation

N = R_* × f_p × n_e × f_l × f_i × f_c × L

Dr. Frank Drake, currently the president of the SETI Institute, developed the above equation as a tool for estimating the number of civilizations that would have the ability to communicate with us. The scientific community uses this equation to examine the factors that go into determining what that estimate may be. The variables are as follows:

N: The number of communicative civilizations
R_*: The rate of formation of suitable stars.
f_p: The fraction of those stars with planets.
n_e: The number of "earths" per planetary system.
f_l: The fraction of those planets where life develops.
f_i: The fraction of life sites where intelligence develops.
f_c: The fraction of planets where technology develops
L: The lifetime of communicating civilizations.

Although recognizing that the probability of receiving a signal from one of these hypothetical civilizations is low, the scientific community has a plan of action in place in case such a signal should ever be detected.

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Last modified: October 1, 1996

Thomas E. Gort