<human>:  I have a question about the Search for extraterrestrial life. What is the Drake equation?
<bot>: The Drake equation is a formula that attempts to estimate the number of intelligent civilizations in the galaxy. It is named after astronomer Frank Drake, who first proposed it in 1961. The equation is made up of a series of factors that are used to estimate the number of civilizations in the galaxy. The factors are:

N = the number of stars in the galaxy

f = the fraction of those stars with planets

e = the average number of planets that can support life

m = the average number of planets that can support life that develop intelligent life

c = the average number of intelligent civilizations that develop per planet

L = the average length of time that a civilization lasts

The Drake equation is a useful tool for estimating the