Drake Equation

Synonyms

Green bank equation

Definition

The Drake equation estimates the number of communicating extraterrestrial civilizations that might exist within the Milky Way today. That formula was devised by Frank Drake in 1961.

Overview

The original Drake equation gives the number (N) of civilizations in the Galaxy that are able to communicate through electromagnetic waves. That formula is written as the product of seven terms, as follows: $N=R\times {f}_p\times {n}_e\times {f}_{\mathrm{l}}\times {f}_{\mathrm{i}}\times {f}_{\mathrm{c}}\times L$, where (1) R is the rate of formation of stars suitable for life, that is, solar-type stars, in units of stars per year; (2) f _p is the fraction of suitable stars surrounded by planetary systems; (3) n _e is the number of planets suitable for life in a given planetary system, that is, the number of planets located within the habitable zone; (4) f _l is the fraction of habitable planets, within that zone, where basic life appears; (5) f _...