Drake Equation – Odds of Finding Intelligent Extraterrestrials

Drake Equation
The Drake equation estimated the number of extraterrestrial civilizations in the galaxy capable of communicating with Earth.

The Drake Equation is a formula for estimating the number of extraterrestrial civilization in the Milky Way galaxy capable of communicating with humans. It takes its name from American astronomer and astrophysicist Frank Drake, who proposed the equation in 1961.

  • Frank Drake outlined his equation at the first SETI meeting in 1961.
  • The equation calculates the number of extraterrestrial civilizations capable of communication with us.
  • The purpose of the equation is stimulating thought and discussion about intelligent extraterrestrial life, not actually finding a concrete number.
  • While the Drake Equation estimates the number of intelligent civilizations, it does not address the odds of finding extraterrestrial life.

The Drake Equation and Its Purpose

The Drake Equation is not a hard-and-fast mathematical equation for calculating a singular, definitive answer. Rather, it is an intellectual tool for stimulating dialogue and thought regarding the factors necessary for the existence of extraterrestrial life and the ways we search for it.

The equation is:

N = R* x fp x ne x fl x fi x fc x L


  • N is the number of civilizations in our galaxy capable of communicating with Earth
  • R* is the average number of new stars formed per year in our galaxy
  • fp is the fraction of those stars that have planetary systems
  • ne is the average number of planets per star capable of supporting life
  • fl is the fraction of these planets that actually develop life
  • fi is the fraction of theses planets that develop intelligent life
  • fc is the fraction of civilizations that develop a technology that releases signals of their existence into space
  • L is the length of time these civilizations communicate


Frank Drake first introduced the equation in 1961 during the first scientific meeting on the search for extraterrestrial intelligence (SETI), held at the Green Bank Observatory in West Virginia. Drake’s primary goal condensing the considerations that scientists confront when searching for extraterrestrial life. The purpose of the equation was not calculating a precise value, but promoting a productive discourse on the subject.

These are the original numbers from Drake’s presentation:

  • R* = 10
  • fp = 0.5
  • ne = 2.0
  • fl = 1.0
  • fi = 0.01
  • fc = 0.01
  • L = 10000

Drake’s original estimate was optimistic, suggesting that there between 10 and 10,000 advanced civilizations in the Milky Way. The variables drew from scientific knowledge at the time and Drake’s own assumptions. The equation was a starting point for a conversation.

A Comparison: Drake’s Original and Current Estimates

Today, scientists have a good idea of the value of R* (the number of new stars forming in the galaxy). But, the other values are not known with any degree of certainty. Feeding in modern numbers leads to a wide range of estimates. Based on the Kepler spacecraft’s discovery of numerous exoplanets and our enhanced understanding of cosmic habitability, the number of potentially communicative civilizations could be much larger than Drake’s initial estimate. However, consider the daunting challenges of interstellar communication and the possibly narrow windows for detectable civilization existence. Some estimate place the number of communicating civilization much lower than Drake’s original estimate. Some calculations predict we are alone.

Criticisms and Modifications of the Drake Equation

Critics of the Drake Equation argue that the high levels of uncertainty in its variables render the equation speculative at best and misleading at worst. They contend that the range of potential values is so broad that it makes any meaningful calculation impossible. Others criticize the equation for implicitly assuming that civilizations evolve along a similar path as Earth.

There are modifications to the Drake Equation that improve its usefulness. One such modification is the Seager Equation, proposed by the astrophysicist Sara Seager. The Seager focuses on the search for biosignatures on exoplanets, without the necessity for civilizations having technological capabilities.

The Drake Equation’s Role in the Search for Extraterrestrial Life

Despite its uncertainties and criticisms, the Drake Equation serves a crucial role in our quest to uncover the existence of extraterrestrial life. It guides research and exploration strategies by encouraging scientists to think about the various factors that could lead to the existence of such life. It helps to prioritize scientific endeavors. These include seeking exoplanets, researching extreme life forms on Earth, and developing techniques for detecting signals that might be of extraterrestrial origin.


  • Conselice, Christopher J.; et al. (2016). “The Evolution of Galaxy Number Density at z < 8 and its Implications”. The Astrophysical Journal. 830 (2): 83. doi:10.3847/0004-637X/830/2/83
  • Forgan, D. (2009). “A numerical testbed for hypotheses of extraterrestrial life and intelligence”. International Journal of Astrobiology. 8 (2): 121–131. doi:10.1017/S1473550408004321
  • Morton, Oliver (2002). “A Mirror in the Sky”. In Graham Formelo (ed.). It Must Be Beautiful. Granta Books. ISBN 1-86207-555-7.
  • Rood, Robert T.; James S. Trefil (1981). Are We Alone? The Possibility of Extraterrestrial Civilizations. New York: Scribner. ISBN 0684178427.
  • Vakoch, Douglas A.; Dowd, Matthew F., eds. (2015). The Drake Equation: Estimating the Prevalence of Extraterrestrial Life Through the Ages. Cambridge, UK: Cambridge University Press. ISBN 978-1-10-707365-4.