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The Drake Equation: Helping Scientists Gauge The Probability Of Extraterrestrial Life

Reid Wiseman
The Milky Way Galaxy as seen from the International Space Station

Last spring scientists discovered three new Earth-sized planets outside of our solar system, raising the question: could intelligent live exist elsewhere?

Some try to answer this question with the Drake Equation, an estimation equation named after astrophysicist Frank Drake, who developed it in 1961.

Estimation equations can be about anything with an unknown answer, but generally take a complex problem and break it down into several smaller questions.

Professor Frederick Walter of Stony Brook University gave an example of an estimation equation by using the upcoming presidential election.

For example, what percentage of Americans are in the country? Of those, how many are over 18? Of the people eligible to vote, how many have registered? Even down to what is the weather going to be like on voting day?

“You are trying to summarize or categorize, place all of the things you don’t know in a number of parameters so when you multiply all of these things together with estimates on all of them, you get a reasonable number.”

Similarly, the Drake Equation starts with the total number of stars in the Milky Way Galaxy and uses half a dozen factors in three groups to estimate how many civilizations exist in total.

“The known knowns are: we know how many stars are in the galaxy…and we’re going to make the assumption that every alien civilization is near a star. They’re on a planet, so we need to know how many stars have planets...and then you can say how many planets are the right distance from the star.” 

The known unknowns are factors that we know we need to know, but we don’t know the exact answer, such as how likely life is to initially develop, or how likely it is to become intelligent.

And finally there are unknown unknowns.

“Is it important that we have a moon, is it important that Jupiter is protecting the Earth from bombardment?”

Some scientists, using the Drake Equation, conclude there could be millions of other civilizations out there, but others will stick to the known data and say that Earth is one of a kind.