Drake equation

The Drake equation estimates the number of communicative extraterrestrial civilizations in the Milky Way by multiplying factors for star formation, habitability, life, intelligence, communication, and longevity.

Star formation rate: The number of stars formed in a galaxy per unit of time. It sets the equation’s starting supply of stars capable of hosting planets.
Frank Drake: An American astronomer who formulated the Drake equation and organized the first modern SETI meeting. He introduced the equation as a framework for discussing detectable civilizations.
Search for extraterrestrial intelligence: The scientific search for evidence of intelligent life beyond Earth. The equation was designed to frame estimates relevant to this search.
Great Filter: A proposed barrier that makes the emergence of detectable technological civilizations rare. It offers an explanation for why several Drake factors might be extremely small.
Exoplanet: A planet orbiting a star beyond the Solar System. The equation asks what fraction of stars have planets suitable for life.
Green Bank Conference: A 1961 meeting of scientists that helped establish the modern search for extraterrestrial intelligence. Drake devised the equation while preparing for this meeting.
Project Ozma: Frank Drake’s 1960 search for radio signals from nearby Sun-like stars. It was an early observational effort to find the civilizations the equation describes.
Rare Earth hypothesis: The hypothesis that complex life is uncommon because Earth-like conditions are exceptionally rare. It challenges optimistic assumptions about how often habitable planets produce complex life.
Circumstellar habitable zone: The range around a star where a planet could sustain liquid water on its surface. It offers one way to estimate the fraction of planets with potentially habitable conditions.
N equation: The Drake equation’s estimate of the number of communicative civilizations in the Milky Way. This is the quantity produced by multiplying the equation’s factors.

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