Kepler Space Telescope

Kepler launched on March 7, 2009, with a single, radical assignment: stare at one patch of 150,000 stars for years and watch for the tiny winks of light that betray a planet crossing its star’s face. It found them by the thousands. Kepler’s census confirmed more than 2,600 exoplanets and revealed that planets outnumber stars in the Milky Way.

Kepler discovered lava worlds, planets orbiting two suns, and rocky planets in habitable zones — statistical proof that potentially Earth-like worlds are common. When failing reaction wheels ended its primary mission in 2013, engineers reinvented it as ‘K2,’ balancing on sunlight pressure to keep hunting until its fuel ran out in 2018. It changed the answer to ‘are there other worlds?’ from maybe to everywhere.