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How did the Kepler satellite help find potentially habitable planets?

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Planet TOI 700e — extraterrestrial life An illustration of the Earth-size planet TOI 700e orbiting within the habitable zone of its star. The habitable zone is the area around a star where liquid water, and thus possibly life, can survive on a planet's surface. Its Earth-size sibling, TOI 700d, can be seen in the distance.

The Kepler satellite played a pivotal role in astrobiology by identifying extrasolar planets that reside within their stars' habitable zones—the orbital regions where conditions might allow for liquid water and, potentially, life.1

To achieve this, Kepler utilized the transit method, monitoring over 100,000 stars for the slight, periodic dimming that occurs when a planet passes in front of its host star. Because detecting these transits is exceptionally challenging—requiring high precision and continuous observation—the satellite was placed in a heliocentric orbit to avoid atmospheric distortion and interference from Earth's magnetosphere.1

By staring at a fixed patch of sky in the constellation Cygnus, Kepler successfully discovered thousands of planets, including significant milestones such as:

Kepler-22b: The first planet found within the habitable zone of a Sun-like star.1
Kepler-186f: The first Earth-size planet discovered within its star's habitable zone.1

These findings have been instrumental in helping scientists estimate the prevalence of Earth-like planets and refine our understanding of where life might exist beyond our solar system.1