Drake Equation - Blog Posts

The Drake Equation

In 1961, following an early SETI experiment using radio telescopes called Project Ozma, astronomer Frank Drake arranged a historic meeting at the National Radio Astronomy Observatory in Green Bank, West Virginia. The ten attendees - among them a young Carl Sagan - discussed the feasibility and methodology of detecting extraterrestrial civilizations using radio astronomy. They formulated the Drake Equation - a rough, speculative means of estimating the possible number of current technologically-advanced civilizations in the galaxy. 

N = the number of advanced extraterrestrial civilizations potentially detectable by radio signals in the Milky Way Galaxy.   

Depending on the values used for each variable, N can work out to be hundreds of thousands or more, or very few. 

R* = Rate of new star formation. 

One estimate is 7 stars per year.

Fp = Percentage of stars with planetary systems around them.

New solar systems are being discovered every year. 

Ne = Number of planets per star system capable of sustaining life. 

Depending upon the temperature, type, and size of the star, the habitable zone of a planet for Earth-like life may be nearer or further from its star. Based on our own solar system, we might guess 1 or 2.

Fl = Fraction of those planets upon which life appears. 

How many of those habitable planets upon which life has developed is difficult to estimate. In our own solar system, it’s at least 1 - there is a good chance that at one point, life developed on Mars, though traces of it have yet to be found.

Fi = Fraction of those planets where intelligent life appears.

Estimates vary wildly. We know it’s happened at least once here on Earth. As ‘intelligence’ is subjective, it may be that it has developed in other non-human, communicating species, like whales. 

Fc = Fraction of those societies that develop advanced communication technology and send signals into space.

Intentional or unintentional, other civilizations might transmit identifiable signals into outer space that modern Earth technology could pick up.

L = Lifetime of communicative civilizations. 

Do technologically-capable civilizations inevitably self-destruct, or can they last forever? This is an immensely uncertain question. We’ve been communicating with radio waves for fewer than 100 years, with the long-term survival of our species and our status as ‘technological’ uncertain.