Conner Smith October 24, 2012 FYOS 1001

 Estimates the number of technological civilizations that might exist  Detectable extraterrestrial civilizations in the Milky Way galaxy  Used in the SETI program  Devised in 1961 by Frank Drake

“As I planned the meeting, I realized a few day[s] ahead of time we needed an agenda. And so I wrote down all the things you needed to know to predict how hard it's going to be to detect extraterrestrial life. And looking at them it became pretty evident that if you multiplied all these together, you got a number, N, which is the number of detectable civilizations in our galaxy. This, of course, was aimed at the radio search, and not to search for primordial or primitive life forms.” — Frank Drake

 R* is rate of star formation  10 stars/year  ~200 billion stars  Estimates may be as high as 400 billion stars  Confident estimate

 f p = fraction of stars that have planets  0.5  Half of all stars form planets of some type.  We have discovered over 330 exoplanets to date.

 n e = number of planets per star that can support life  ~2 habitable planets per star.  Can include habitable moons around large planets.

 f ℓ = fraction of habitable planets that actually develop life  1.0  The fraction is 1 because life is believed to have arisen on Earth many times.

 f i = fraction of planets with life that actually develop intelligent life  0.01  This fraction could be much lower since intelligence has been on Earth only recently.  Probably the hardest parameter to estimate.

 f c = fraction of civilizations that develop communication  0.01  This fraction could be high, probably 1.0.

 L = length of time that civilization communicates  10,000 years.  Or until civilization destroys itself.  Maybe 10 years (remember the Cold War).  Maybe indefinitely.

 Results using low value estimates  N = 7 × 0.4 × × × 0.1 × 304 = 8 x  Results using low value estimates  N = 7 × 1 × 0.2 × 0.13 × 1 × 1 × 10 9 = 182 million  Fermi paradox

 PBY PBY

 