Kepler Space Telescope

Kepler used the transit method, continuously monitoring the brightness of over 150,000 stars and detecting the tiny, periodic dips in light that occur when a planet passes in front of its host star from Kepler's line of sight. By measuring the depth and timing of these dips, scientists could determine the planet's size and orbital period.

Kepler discovered over 2,600 confirmed exoplanets and identified thousands more candidate planets that await confirmation — accounting for a substantial fraction of all known exoplanets. Many of these planets are in or near their stars' habitable zones, where liquid water could theoretically exist on a rocky surface.

No — Kepler was officially retired by NASA in November 2018 after exhausting the maneuvering fuel needed to maintain its pointing accuracy. Its primary mission ended in 2012 when two of its four reaction wheels failed, but it continued operating in an extended mission called K2 that used solar pressure as a makeshift stabilizer until fuel ran out.

Kepler was launched on March 7, 2009, and during its primary mission it stared continuously at a single field of stars in the constellations Cygnus, Lyra, and Draco. The K2 extended mission observed multiple different fields along the ecliptic plane, allowing Kepler to survey a broader range of star types and galactic environments.