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How did the Kepler satellite discover planets around other stars?

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artist's conception of Kepler-186f — extraterrestrial intelligence An artist's conception depicts Kepler-186f, the first Earth-sized extrasolar planet found in its star's habitable zone.

The Kepler satellite discovered extrasolar planets by utilizing the transit method, which involves monitoring stars for a slight, periodic dimming in brightness. This dimming occurs when a planet passes in front of its host star from the perspective of the observer, an event that creates a specific light curve indicating the planet's presence.12

To achieve this, the spacecraft used a 95-cm telescope to stare continuously at a single patch of sky, observing more than 100,000 stars simultaneously. Because the transit of a planet—such as Earth passing in front of the Sun—causes an extremely small decrease in brightness (approximately 0.008 percent), the satellite was designed to operate outside of Earth's atmosphere to avoid distortion and to ensure continuous, uninterrupted data collection. The mission focused on identifying planets within or near their stars' habitable zones, where conditions might allow for the existence of liquid water and, potentially, life.1