Kepler-166: A Distant Star With Three Super-Earths

Kepler-166 is a star located 1970 light-years away, and it hosts three planets. The star is 4.47 billion years old, with a mass of 0.88 solar masses and a radius of 0.83 solar radii. Its temperature is 5350 K. Its reported mass and radius estimates are smaller than the Sun's, and its reported temperature is cooler than the Sun's.

All three planets were detected by transit, the 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, and each planet's year is the time it takes to complete one orbit. All three are classified as Super-Earths, a size class that reaches 2.5 times Earth's radius, and each has a reported radius estimate larger than Earth's.

Kepler-166 b was discovered in 2014. Its orbital period is 7.65 days, and its radius is 2.27 Earth radii. Kepler-166 c was also discovered in 2014. It has an orbital period of 34.3 days and a radius of 2.38 Earth radii. Kepler-166 d was discovered in 2016. Its orbital period is 1.55 days, and its radius is 1.73 Earth radii. Among the listed planets, Kepler-166 d has the shortest year by reported estimates and the smallest radius by reported estimates, while Kepler-166 c has the longest year and the largest radius by reported estimates. Kepler-166 b has the second-shortest year by reported estimates and the second-smallest radius by reported estimates.