Kepler-309 and Its Two Known Planets

Kepler-309 is an M0 V star, a small, cool red dwarf, located 1780 light-years away. Its measured mass is 0.79 solar masses, its radius is 0.73 solar radii, and its temperature is 4740 K. Its reported mass and radius are smaller than the Sun’s, and its reported temperature is cooler than the Sun’s. The star is 3.02 billion years old. Two planets are known to orbit it.

Both planets were discovered by transit in 2014. Kepler-309 b is a Super-Earth with a radius of 1.56 Earth radii, larger than Earth’s, and an orbital period of 5.92 days. Kepler-309 c is Neptune-like, with a radius of 2.51 Earth radii, also larger than Earth’s, and an orbital period of 105 days. Among the listed planets, Kepler-309 b has the shortest year and the smallest radius by reported estimates, while Kepler-309 c has the longest year and the largest radius.