Today, scientists using data from NASA's Kepler spacecraft announced they'd discovered an eighth planet orbiting a star 2,500 light years away. They've named the planet Kepler-90i after the star it orbits, Kepler-90, which is slightly hotter and more massive than our sun. "This discovery of an eighth planet ties Kepler-90 with our own solar system for having the most known planets," said NASA astrophysicist Paul Hertz during a press conference about the discovery.
Researchers found the exoplanet by re-sifting through four years of data from a Kepler instrument called a photometer, a machine that measures the brightness of stars. Between 2009 and 2013, Kepler took pictures of 200,000 stars every half hour, about 10 pixels per picture. If a star dims and brightens in a repeating cycle, that could mean a planet is orbiting it. And depending on how gradually it dims and how quickly it brightens, you can infer information about the length of its orbit and the size of the planet.