The Seager Equation: The Search For Life

Posted by Henry Paterson | September 9, 2013 1


Thousands of years ago, our nearest celestial neighbor, the Moon was believed to be inhabited. We have since learned it is not. Hundreds of years ago we discovered several of the stars in our night sky were actually planets, and speculation grew.  Percival Lowell popularized the idea that Mars, our next neighbor to the outer reaches of the solar system was inhabited by a race starved for water who built canals for the purpose of irrigation and supplying their civilization. While life may have existed there once, briefly, alas it has not harbored life in our lifetime (if ever) beyond perhaps a few lingering bacteria.

Venus, Jupiter, Mercury, even the Sun has had it’s speculative inhabitants. Now we send our surrogate eyes and ears to our nearest neighbors and find cold and forbidding desolations or hot and violent land or cloudscapes. While we have not yet ruled out potential for extremeophiles living in the ice cloaked oceans of places like Europa, we still have only speculation in those areas.

Only decades ago we discovered the first planet orbiting a Main Sequence star, Pegasi 51. While we are not yet able to make detailed enough observations of those planets to determine if they are capable of supporting life, we can make many educated guesses based on what we understand of the life and environments we know. We have found a few planets we believe capable of supporting life.

We continue to make advances in exploring the stars, we continue to hope to find life in orbit around one of those stars. No matter how you look at it, it seems like the more we learn about the universe around us, the further away the potential for life to exist becomes. At the same time the potential places for life is expanding.

How do we resolve that seeming contradiction? In 1961, Frank Drake formulated an equation of pure variables to estimate the number of civilizations that might exist.

The Drake equation:

The equation is usually written:

R* = the average rate of star formation in our galaxy
fp = the fraction of those stars that have planets

We continue to revise our estimates of a few of these factors with our searches of the local galaxy.

Now there is a new equation, refined by exo-planet hunter Sara Seager,

Sara Seager, expert planet hunter. Credit: MIT

using our current understanding to help us narrow down the possibilities. Not so much looking for civilizations, as Drake’s equation does, but merely life.



N = the number of planets with detectable signs of life
N* = the number of stars observed
FQ = the fraction of stars that are quiet
FO = the fraction of those planets that can be observed
FL = the fraction that have life
FS = the fraction on which life produces a detectable signature gas


The fact remains that the Seager equation is also only a string of variables to which we apply guesswork. But our guesswork is getting better as we continue to observe.

Seager was interviewed at Astrobiology Magazine

Q: What was the inspiration behind this equation?


I wanted to explain that we have a new search in progress. We’ll use TESS [the Transiting Exoplanet Survey Satellite] to find rocky planets transiting small stars. Then we’ll use the James Webb Space Telescope to observe the atmospheres of those planets, during transits or secondary eclipses. The punchline here is that if we’re really lucky and everything works in our favor, we will be able to infer signs of life on those planets. We have a shot—I’d call it a remote shot—of finding life within the next decade.

Q: Is your approach specific to intelligent life as well?


You can read the full interview at Astrobiology Magazine

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Henry Paterson

Editor at GhostTheory

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  • Steven White

    Just amazing, I’m speechless.