Kepler's Exoplanet Legacy
Natalie Batalha (NASA Ames Research Center)

The scientific community recently celebrated twenty years exploring the diversity of planets and planetary systems orbiting main sequence stars. Today, the discoveries spill into the thousands, and the sensitivity boundaries continue to expand. NASA's Kepler Mission unveiled a galaxy replete with small planets and revealed populations that don't exist in our own solar system. The discovery catalog is sufficient for computing planet occurrence rates as a function of size, orbital period, and host star properties. We've learned that every late-type star has at least one planet, that terrestrial-sized planets are more common than larger planets within 1 AU, and that the nearest, potentially habitable earth-sized planet is likely within 5 pc.

After four years of continuous observations, the Kepler prime mission ended in May 2013 with the loss of a second reaction wheel. Thanks to innovative engineering, the spacecraft gained a second lease on life and emerged as the ecliptic surveyor, K2. In many regards, K2 is a distinctly new mission, not only by pointing at new areas of the sky but also by focusing on community-driven goals that diversify the science yield. For exoplanets, this means targeting bright (V < 13) and low mass (M dwarfs) stars -- the populations harboring planets amenable to dynamical and atmospheric characterization. To date, the mission has executed 9 observing campaigns lasting ~80 days each and has achieved a 6-hour photometric precision of 30 ppm. Dozens of planets have been confirmed, including nearby (< 50 pc) systems on the watch-list for future observing campaigns with the James Webb Space Telescope. While Kepler prime is setting the stage for the direct imaging missions of the future, K2 is easing us into an era of atmospheric characterization.