The Seager Equation: A New Perspective on the Search for Extraterrestrial Life


As our technological capabilities grow and our knowledge of the universe expands, our perspective on the search for extraterrestrial life continues to evolve. Over the years, various hypotheses, equations, and concepts have been proposed to address this cosmic question. The Seager Equation, developed by astrophysicist and planetary scientist Professor Sara Seager, offers a fresh approach to our search for life beyond Earth.

The Seager Equation

The Seager Equation is designed to estimate the number of planets with detectable biosignature gases, substances that may indicate the presence of life. Unlike the Drake Equation, which attempts to calculate the number of advanced civilizations with whom we might communicate, the Seager Equation is focused on the broader category of life, including microorganisms and simple life forms, not necessarily civilizations.

The Seager Equation is formulated as:

N = N* · Fq · Fh · Fo · Fl · Fs


  • N is the number of planets with detectable biosignature gases.
  • N* is the number of stars observed. This number is determined by observational constraints, like the lifetime of the mission or the kind of telescope used for observation.
  • Fq is the fraction of stars that are quiet. Quiet stars are optimal for observing transiting planets, as they have less stellar activity that could mask or mimic biosignature gases.
  • Fh is the fraction of stars with planets in the habitable zone. The habitable zone, often referred to as the ‘Goldilocks Zone,’ is the region around a star where conditions might allow liquid water to exist on a planet’s surface.
  • Fo is the fraction of those planets that can be observed. Not all planets are positioned in a way that allows us to detect their biosignatures from Earth.
  • Fl is the fraction of those planets that have life. Life may not exist on all planets, even those within the habitable zone.
  • Fs is the fraction of planets with life where the life produces a detectable biosignature gas. Not all life forms produce gases that we can detect from a distance.

The Impact of the Seager Equation

The Seager Equation represents a significant evolution in our approach to the search for extraterrestrial life. Its focus on biosignature gases broadens the scope of potential discovery from intelligent life forms to any form of life that interacts with its atmosphere.

This equation plays an essential role in guiding the development of new observatories and missions, like the James Webb Space Telescope and the Transiting Exoplanet Survey Satellite (TESS). By quantifying the conditions necessary for detecting biosignature gases, the Seager Equation helps us determine which stars and planets should be our priority targets.

By shifting our focus from intelligent civilizations to all possible life forms, it significantly expands the scope of our search. As we continue to explore the cosmos, the insights offered by the Seager Equation will play an important role in guiding our journey and perhaps, one day, in uncovering signs of life beyond our home planet.

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