Drake’s Equation is an equation used to estimate the number of detectable extraterrestrial civilizations in the Milky Way galaxy. Invented by Frank Drake, the founder of SETI.


  • 1011 Stars discovered so far

Fp (0.5) Half the planets in the Milky Way galaxy have stars around them

Ways to detect planets

  • Transit Method: Diming of star due to planet revolving around it
  • Astrometry/ Doppler Spectrometry: Wobbling of star due to planet revolving around it
  • Direct Imaging: Using optical telescope to directly see massive planets around parent stars

***Thanks to Kepler telescope; we can detect smaller planets; earth-like size

Ne (2.0) Based on the distance from the parent star

  • Each star has a particular distance you can be away from it to develop life
  • Called the Habitable Zone (Defined by present of LIQUID WATER) MUST BE LIQUID
  • Based on molar mass (H20) should be a gas at 25C but remains a liquid due to: 1) COHESION (hydrogen bonds-stick together) 2) HIGH HEAT CAPACITY 3) HIGH HEAT OF VAPORIZATION
  • Increase star size= move habitable zone BACK
  • Decrease star size= move habitable zone FORWARD

Fl (1.0)

  • Because all planets capable of forming life will eventually develop life

Fi/Fc (10% for both)

  • Only applicable to planets in habitable zone
  • NOT EASY TO ESTIMATE (This valve is greatly debated)


  • Longer civilization is around, increased likelihood of finding them
  • BUT not how old civilization is; its age is determined by when they first evolved communication
  • We are about 100 years old with communication / (Age of the Universe (10 bya))

Fermi Paradox

The Drake Equation predicts a large amount of intelligent civilizations, however we have found NONE!

Why haven’t we found anyone?

  • Maybe distance is too great
  • Maybe Our technology could be incompatible; we can’t detect each other
  • Maybe NO other civilizations exist
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William Anderson (Schoolworkhelper Editorial Team)
William completed his Bachelor of Science and Master of Arts in 2013. He current serves as a lecturer, tutor and freelance writer. In his spare time, he enjoys reading, walking his dog and parasailing. Article last reviewed: 2022 | St. Rosemary Institution © 2010-2024 | Creative Commons 4.0

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