The Kepler mission was a space observatory launched by NASA in 2009 with the primary goal of discovering Earth-sized exoplanets orbiting other stars. Kepler used the transit method to detect exoplanets, which involves observing the slight dimming of a star as a planet passes in front of it. This method allowed Kepler to discover thousands of exoplanets, providing valuable data on the frequency and distribution of planets in our galaxy. Kepler's observations have significantly advanced our understanding of planetary systems beyond our own and have paved the way for future discoveries in the field of exoplanet research.