Kepler-186 is a cool M-dwarf (about 0.48 solar masses, 3,788 K, 0.47 solar radii), 580 light-years from Earth. Kepler-186 f was the first Earth-sized planet found in a habitable zone, outermost of five planets around a red dwarf. Kepler-186f, the outermost planet, was the first Earth-radius world found in a star's habitable zone when the system was announced in 2014, though its cooler host star makes conditions quite different from Earth. Kepler-186 b is a planet with 1.1 Earth radii, with an orbital period of 3.9 days, at 0.034 AU from its star, discovered in 2014 via transit. Mutual gravitational tugs between the planets can slowly reshape their orbits, preserving clues to the system's assembly.