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Drake equation: an equation used to discuss the number of intelligent civilizations currently existing in the Milky Way with which humans could communicate ... more

How Many Aliens Are There?

Dr. Frank Drake, astronomer and founder of SETI“What if we could talk to aliens?” In 1961, astronomer Dr. Frank Drake gathered a group of scientists to talk about how many alien civilizations could be living in our galaxy. To help these scientists think, he made a math equation which predicts the number of intelligent alien civilizations in the Milky Way Galaxy.

Scientists can put their own numbers in for each term in the equation. Each number in the equation is just an educated guess, as scientists do not know the real numbers for many of these terms. Even though these numbers are guesses, the equation still gives scientists an idea of how many alien civilizations could possibly exist.


     The Drake Equation is calculated by multiplying the following:

The number of stars made in the milky way.

1)     R* - stars made in the Milky Way galaxy in one year, 


The fraction of stars that have planets2)     Fp - the fraction of stars that have planets,


Fraction of planets where life can exist3)     Ne - the fraction of those planets where life can exist,


Fraction of planets where life exists4)     FL - the fraction of those planets where life does exist,


The number of planets where intelligent life exists5)     FI - the fraction of those planets where intelligent life exists,


The fraction of aliens with intelligent technology6)     FC - the fraction of those intelligent aliens who develop technology that is able to communicate outside of their own planet,


How long an intelligent civilization lasts7)     L - number of years an intelligent, communicating civilization lasts.


R* x FP x Ne x FL x FI x FC x L = the number of intelligent aliens currently living in the Milky Way


Here is an example from one astrobiologist:

1)     R* = 10 (astronomers know roughly 10 stars are made per year)

2)     Fp = 100% (nearly all stars have planets)

3)     N3 = 25% (life can exist in very harsh environments - it would make sense that life could exist on a number of planets)

4)     FL = 100% (if life can exist, it will)

5)     FI = 1% (not all life will become intelligent)

6)     FC = 50% (most intelligent life will be able to invent communication technology such as radio)

7)     L = 1,000,000 years (intelligent life will exist for a long time)

Alien life illustration10 x 100% x 25% x 100% x 1% x 50% x 1,000,000 = 12,500 intelligent alien civilizations which may currently exist. This is just a guess, but shows why some scientists think it will be easy to discover alien life.

It’s also part of why official searches for alien life exist. Beyond thinking of this equation, Dr. Drake is involved in SETI. The Search For Extraterrestrial Intelligence (SETI) Institute studies life in the universe and how it can communicate with us.

Alien illustrations by Megan Joyce. Additional images via Wikimedia Commons. Radio transmission illustration by Quastie.

Illustration of a radio transmission being sent that could be received by extraterrestrial intelligent life.

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