This is an external view of Kepler 10b as depicted by a NASA artist. The planet simmers in this image, likely because it is orbiting its star as much as 20 times closer than Mercury orbits our sun. How has NASA discovered planets such as Kepler 10b? Kepler operates by scanning the brightness of more than 100,000 stars every 30 minutes. The brightness is measured by a photometer, or light meter, which is aboard the Kepler spacecraft. It looks for “tiny winks” or variations in the star’s brightness that occur when an exoplanet passes in front of it.