These distant worlds are called exoplanets: planets that exist outside our solar system. When it does, it dims the star's light ever so slightly, allowing scientists to measure the difference with telescopes. Traces of sodium in its nitrogen-rich atmosphere left their telltale mark on the yellow star's light. Spotlight: Proxima bThe closest known exoplanet to Earth is Proxima b, orbiting Proxima Centauri, a red dwarf star just over four light-years away. For every confirmed exoplanet, there's another point of light in the sky that has been identified as a candidate exoplanet.