Kepler-31 and Its Three Worlds

Kepler-31 is a star located 5430 light-years away, and three planets have been found in orbit around it. The star is 4.17 billion years old and has a reported mass estimate of 1.08 solar masses and a reported radius estimate of 1.2 solar radii. Its reported temperature is 6120 K and is hotter than the Sun's. Its reported mass and radius estimates are both larger than the Sun's.

All three planets were discovered 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-31 b and Kepler-31 c were both discovered in 2011, while Kepler-31 d was discovered in 2014. The planets are Jupiter-like or Neptune-like in size class, meaning their radii exceed 4 times Earth's radius or reach up to 4 times Earth's radius, respectively. Each planet's reported radius estimate is larger than Earth's.

Kepler-31 b is Jupiter-like with a radius of 5.5 Earth radii, the largest among the listed planets. Its year lasts 20.9 days, the shortest among the listed planets. Kepler-31 c, also Jupiter-like, has a radius of 5.3 Earth radii, the second-smallest among the listed planets, and an orbital period of 42.6 days, the second-shortest among the listed planets. It has a reported upper limit of 1493.7 Earth masses.

Kepler-31 d is Neptune-like with a radius of 3.9 Earth radii, the smallest among the listed planets, and its year lasts 87.6 days, the longest among the listed planets. It has a reported upper limit of 2161.244 Earth masses.