Kepler-186: A Cool Dwarf and Its Five Earth-Like Worlds

Kepler-186 is a small, cool red dwarf of spectral type M1, located 579 light-years away. Its reported mass estimate is 0.478 solar masses, and its reported radius estimate is 0.472 solar radii, both smaller than the Sun's. With a reported temperature of 3790 K, it is cooler than the Sun, and it has a reported lower limit of 4 billion years in age. Five planets are known to orbit this star.

All five planets were discovered by transit, the method in which a planet passes in front of its star from our viewpoint and causes a small dip in observed brightness; repeated dips help establish orbital periods. Each is classified as Earth-like, meaning its radius stays within 1.5 times Earth's radius.

Kepler-186 b has the shortest year among the listed planets, 3.89 days, and the smallest radius, 1.07 Earth radii. Kepler-186 c has the second-shortest year, 7.27 days, and a radius of 1.25 Earth radii.

Kepler-186 d has the largest radius among the listed planets, 1.4 Earth radii, and a year of 13.3 days. Kepler-186 e has a radius of 1.27 Earth radii and the second-longest year, 22.4 days. Kepler-186 f has the longest year, 130 days, and a radius of 1.17 Earth radii, the second-smallest among the listed planets. The reported radius estimates for Kepler-186 c, d, e, and f are each larger than Earth's.