Kepler186

Kepler-186 is a cool, small star located in the Cygnus region, about 490 light-years from Earth. It has roughly half the radius and mass of the Sun, and a surface temperature around 3,500 to 3,700 kelvin, giving it a redder spectrum than the Sun. The star’s faintness and distance make detailed follow-up measurements challenging.

The Kepler-186 system contains five confirmed exoplanets, designated Kepler-186b, c, d, e, and f. They were detected by the transit method using data from NASA’s Kepler Space Telescope and announced in 2014. The planets vary in size from Earth-sized to somewhat larger, and they orbit relatively close to the star compared with the inner planets of the Solar System. The outermost planet, Kepler-186f, is approximately Earth-sized and lies within the star’s habitable zone, where liquid water could potentially exist under suitable conditions.

Mass measurements for the planets have not been obtained to date; radii are the primary constraints, leaving uncertainties about their compositions and densities. Because the star is small and cool, its habitable zone is much closer in than the Sun’s, so the planets receive stellar flux quite different from Earth’s. Some of the planets, including Kepler-186f, may be tidally influenced by the star due to their proximity, which has implications for climate and potential habitability.

Kepler-186 is notable for hosting one of the first Earth-sized planets found in the habitable zone of a star smaller than the Sun, illustrating that Earth-sized planets in such zones can exist in multi-planet systems around low-mass stars. No atmosphere detections have been reported for any Kepler-186 planet.