In the early 1960s, Frank Drake put forth an equation that allowed us to make an estimate of the number of spacefaring, intelligent alien civilizations out there — in either our galaxy or the entire observable Universe — at any point in time. he Drake Equation is composed of seven terms. The first six are used to compute the rate at which intelligent civilizations are being created and the final term identifies how long each lasts on average as a broadcasting civilization.
N = The number of civilizations in the Milky Way Galaxy whose electromagnetic emissions are detectable.
R* = The rate of formation of stars suitable for the development of intelligent life.
fp = The fraction of those stars with planetary systems.
ne = The number of planets, per solar system, with an environment suitable for life.
fl = The fraction of suitable planets on which life actually appears.
fi = The fraction of life bearing planets on which intelligent life emerges.
fc = The fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
L = The length of time such civilizations release detectable signals into space. (in case of Earth – starting from ca. 1974).