Kepler-1321: A Cool, Small Star with Three Known Worlds

Kepler-1321 is a star located 2510 light-years away, and three planets have been found orbiting it. The star itself has a reported mass estimate of 0.54 solar masses and a reported radius estimate of 0.53 solar radii, both smaller than the Sun's corresponding values. Its reported temperature is 4090 K, cooler than the Sun's, and its age is 4.17 billion years.

The three planets were all detected 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; repeated dips help establish orbital periods. Kepler-1321 b, a Jupiter-like planet, was discovered in 2016. Its orbital period is 11.1 days, and its radius is 4.92 Earth radii, larger than Earth's. Kepler-1321 c, a Super-Earth, was also discovered in 2016. Its orbital period is 2.23 days, and its radius is 2.4 Earth radii, larger than Earth's. Kepler-1321 d, a Neptune-like planet, was discovered in 2021. Its orbital period is 5.72 days, and its radius is 2.63 Earth radii, larger than Earth's.

Among the listed planets, Kepler-1321 c has the shortest year by reported estimates, at 2.23 days, and the smallest radius, at 2.4 Earth radii. Kepler-1321 d has the second-shortest year, at 5.72 days, and the second-smallest radius, at 2.63 Earth radii. Kepler-1321 b has the longest year, at 11.1 days, and the largest radius, at 4.92 Earth radii.