Proxima Centauri b (also called Proxima b or Alpha Centauri Cb) is an exoplanet orbiting in the habitable zone of the red dwarf star Proxima Centauri, which is the closest star to the Sun and part of a triple star system. It is approximately 4.2 light-years (4.0×1013 km) from Earth in the constellation Centaurus, making it and Proxima c the closest known exoplanets to the Solar System. In May 2019, a paper presenting recent Spitzer Space Telescope data concluded that Proxima Centauri b did not transit its sun relative to Earth, and attributed previous transit detections to correlated noise.