Kepler-331: A Distant Star With Three Super-Earths

Kepler-331 is a star located 1,890 light-years away, and three planets orbit it. The star has an age of 3.24 billion years, a mass of 0.74 solar masses, a radius of 0.7 solar radii, and a temperature of 4630 K. Its reported mass and radius estimates are smaller than the Sun's, and its reported temperature is cooler than the Sun's.

All three planets were discovered by transit in 2014. A transit occurs when a planet passes in front of its star from our viewpoint, causing a small dip in observed brightness, and repeated dips help establish orbital periods. Each planet is classified as a Super-Earth, a size class for planets whose radius reaches 2.5 times Earth's radius. All three have reported radius estimates larger than Earth's.

Kepler-331 b has an orbital period of 8.46 days and a radius of 1.82 Earth radii, the second-shortest period and second-smallest radius among the listed planets. Kepler-331 c has an orbital period of 17.3 days and a radius of 1.84 Earth radii, the largest radius and second-shortest year among the listed planets. Kepler-331 d has an orbital period of 32.1 days and a radius of 1.64 Earth radii, the smallest radius and longest year among the listed planets.