In 1961, Frank Drake wrote down an equation for the chance of a contactable alien civilization from another planet in the Milky Way Galaxy. This is known as the Drake Equation (sometimes called the Green Bank equation or the Green Bank Formula). Carl Sagan mentioned the Drake equation often so it that has been mistaken for the 'Sagan equation'.
The equation [change]
The Drake equation states that:
- N = the number of civilizations in our galaxy with which communication might be possible;
- R* = the average rate of star formation per year in our galaxy
- fp = the fraction of those stars that have planets
- ne = the average number of planets that can potentially support life per star that has planets
- fℓ = the fraction of the above that actually go on to develop life at some point
- fi = the fraction of the above that actually go on to develop intelligent life
- fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
- L = the length of time for which such civilizations release detectable signals into space.
- "PBS NOVA: Origins - The Drake Equation". Pbs.org. http://www.pbs.org/wgbh/nova/origins/drake.html. Retrieved 2010-03-07.
- "Space: SETI: Frank Drake Biography". http://www.activemind.com/Mysterious/Topics/seti/biography_drake.html. Retrieved November 17, 2011.