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Drake Equation

N = RfnFFi FL

The first National Academy of Sciences conference on the detection of extraterrestrial intelligent life was held here October 30 to November 3, 1961. In his opening remarks, Frank Drake proposed the above equation as the agenda for the meeting. The terms have the following meaning

N = number of communicative civilizations in the Galaxy,

R* = rate of solar type star formation in the Galaxy,

fp = fraction of such stars having planetary systems,

ne = average number of planets in the ecosphere of the star,

Fl = fraction of such temperature planets on which life begins,

Fi = fraction of the life starts that evolve intelligence,

Fc = fraction of these that attempt interstellar communication,

L = average longevity of the communicative phase


The factors on the right are essentially unknowns, so N remains a tantalizing mystery. Nevertheless the Drake equation served, and still serves, as a excellent way to categorize our ignorance and thereby stimulate productive discussion and research.


Presented to the National Radio Astronomy Observatory by the SETI Institute, October 1991


Submitted by: Tom Barclay

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