Kepler-221: A Distant Star With Four Known Worlds

Kepler-221 is a star located 1260 light-years away, and four planets have been identified orbiting it. The host star is estimated to be 4.57 billion years old, with a mass of 0.87 solar masses and a radius of 0.82 solar radii. Its reported temperature is 5300 K. The star's reported mass and radius estimates are both smaller than the Sun's, and its reported temperature is cooler than the Sun's.

All four 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. Repeated dips help establish orbital periods, which are the times the planets take to complete one orbit.

Kepler-221 b is a Super-Earth with an orbital period of 2.8 days and a radius of 1.71 Earth radii. Among the listed planets, it has the shortest year and the smallest radius by reported estimates. Its reported radius estimate is larger than Earth's. Kepler-221 c is Neptune-like, with an orbital period of 5.69 days and a radius of 2.93 Earth radii. Among the listed planets, it has the second-shortest year and the largest radius by reported estimates. Its reported radius estimate is larger than Earth's.

Kepler-221 d is also Neptune-like, with an orbital period of 10 days and a radius of 2.73 Earth radii. Among the listed planets, it has the second-longest year and the second-largest radius by reported estimates. Its reported radius estimate is larger than Earth's. Kepler-221 e is Neptune-like as well, with an orbital period of 18.4 days and a radius of 2.63 Earth radii. Among the listed planets, it has the longest year and the second-smallest radius by reported estimates. Its reported radius estimate is larger than Earth's.