Kepler-191 and Its Three Planets

Kepler-191 is a star located 1940 light-years away. It is 4.9 billion years old, has a mass of 0.84 solar masses, a radius of 0.8 solar radii, and a temperature of 5220 K. Its reported mass, radius, and temperature are all smaller or cooler than the Sun's. Three planets orbit this host: Kepler-191 b, Kepler-191 c, and Kepler-191 d.

All three planets were found by the transit method, in which a planet passes in front of its star from our viewpoint and causes a small dip in observed brightness. Kepler-191 b and Kepler-191 c were discovered in 2014, while Kepler-191 d was discovered in 2016.

Kepler-191 b is an Earth-like planet, a size class for worlds within 1.5 times Earth's radius. It has a radius of 1.34 Earth radii and an orbital period of 9.94 days. Among the listed planets, it has the smallest radius and the second-shortest year.

Kepler-191 c is a Super-Earth, a class reaching up to 2.5 times Earth's radius. Its radius is 1.86 Earth radii, and it completes an orbit in 17.7 days. Among the listed planets, it has the second-smallest radius and the longest year.

Kepler-191 d is also a Super-Earth. Its radius of 2.28 Earth radii is larger than Earth's, and it orbits in 5.95 days. Among the listed planets, it has the largest radius and the shortest year.