Kepler-255: A Distant Star with Three Small Worlds

Kepler-255 is a star located 3430 light-years away. It is 4.37 billion years old and has a mass of 0.9 solar masses, a radius of 0.86 solar radii, and a temperature of 5430 K. Its mass, radius, and temperature are all smaller or cooler than the Sun's corresponding values. Three planets are known to orbit this host.

All three planets were found 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-255 b was discovered in 2014 and is a Super-Earth with a radius of 1.55 Earth radii and an orbital period of 5.71 days. Kepler-255 c, also discovered in 2014, is Neptune-like, with a radius of 2.99 Earth radii and an orbital period of 9.95 days. Kepler-255 d was discovered in 2016 and is Earth-like, with a radius of 1.32 Earth radii and an orbital period of 1.05 days. The radii of Kepler-255 c and Kepler-255 d are both larger than Earth's.

Among the listed planets, Kepler-255 d has the shortest year, at 1.05 days, and the smallest radius, at 1.32 Earth radii. Kepler-255 b has the second-shortest year, at 5.71 days, and the second-smallest radius, at 1.55 Earth radii. Kepler-255 c has the longest year, at 9.95 days, and the largest radius, at 2.99 Earth radii.