The Drake Equation

• N=Ns fs fp ne fl fi fc FL

• N = number of communicating civilizations in our Galaxy right now

• Ns= number of stars in the galaxy (2x1011)

• fs = fraction of stars suitable for life (0.05-0.3) [1x1010 - 6x1011]

• fp = fraction of suitable stars with planets (~0.1) [1x109 - 6x1010]

• ne = average number of habitable planets or moons per solar system (0.01-0.5)

• [1x107 - 3x109]

• fl = fraction on which life develops (0.01 - 1.0) [1x105 - 3x109]

• fi = fraction on which intelligence develops (0.001-0.5) [100 - 1.5x109]

• fc = fraction which try to communicate (~0.5) [50 - 7.5x108]

• FL= fraction of the star’s life during which communicative civilization lasts (1x10-8 - 1x10-3)

• 5x10-7 <N< 750,000

Notes: