of the SETI and Extrasolar Planetary Foundations

The Drake Equation was developed in 1961 by Dr. Frank Drake.

It can determine how
many possible intelligent, communicating civilizations there are in our galaxy.

The equation represents the following:

N*represents the number of stars in the Milky Way GalaxyQuestion: How many stars are in the Milky Way Galaxy?Answer: Current estimates are 200 to 400 billion.fpis the fraction of stars that have planets around themQuestion: What percentage of stars have planetary systems?Answer: Current estimates range from 20% to 50%.nenumber of planets per star that are capable of sustaining lifeQuestion: For each star that has a planetary system, how many planets are capable of sustaining life?Answer: estimates range from 1 to 2.flis the fraction of planets innewhere life evolvesQuestion: On what percentage of the planets that are capable of sustaining life does life actually evolve?Answer: Current estimates are 100% (where life can evolve it will) .fiis the fraction offlwhere intelligent life evolvesQuestion: On the planets where life does evolve, what percentage evolves intelligent life?Answer: Estimates are 50% .fcis the fraction offithat communicateQuestion: What percentage of intelligent life forms have the means and the desire to communicate?Answer: 10% to 20%fLis fraction of the planet's life during which the communicating civilizations may surviveQuestion: For each civilization that does communicate, for what

fraction of the planet's life does the civilization survive?

Answer: This is the most vague question. Using the Earth as our model, the expected lifetime

of our Solar System is approximately 10 billion years. Already communication by radio has

been for less than 100 years. How long can our civilization survive without destroy ourselves

as some predict or will we overcome our problems and survive indefinately? If doomsday came

today this figure would be 1/100,000,000th. If we survive for 10,000 more years this figure

would be 1/1,000,000th.When all of these variables are multiplied, we get:

Nc, the number of communicating civilizations in the galaxy.

## Use the Drake Equation Yourself

Calculate the possible number of communicating civilizations within our own galaxy using the Drake Equation.

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