Kepler-55: A Cool, Dim Star With Five Super-Earths

Kepler-55 is a star located 1890 light-years away. It is 2.34 billion years old and has 0.72 solar masses and 0.68 solar radii, with a temperature of 4510 K. Its reported mass estimate is smaller than the Sun's, as is its radius estimate, and it is cooler than the Sun. Five planets are known to orbit this star, all 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.

All five planets are classified as Super-Earths, a size class that reaches 2.5 times Earth's radius. Kepler-55 b and Kepler-55 c were both discovered in 2012. Kepler-55 b has an orbital period of 27.9 days and a radius of 2.43 Earth radii, while Kepler-55 c has a period of 42.2 days and a radius of 2.21 Earth radii. Among the listed planets, Kepler-55 b has the largest radius, and Kepler-55 c has the second-largest radius and the longest year.

The remaining three planets were discovered in 2014. Kepler-55 d has a period of 2.21 days and a radius of 1.59 Earth radii, giving it the shortest year among the listed planets. Kepler-55 e has a period of 4.62 days, the second-shortest among the listed planets, and a radius of 1.55 Earth radii, the smallest among the listed planets. Kepler-55 f has a period of 10.2 days and a radius of 1.59 Earth radii. Each of the five planets has a reported radius estimate larger than Earth's.