Kepler-37 and Its Four Known Planets

Kepler-37 is a star located 208 light-years away. It hosts four known planets, 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. Repeated dips help establish orbital periods. The star is 6 billion years old, has a reported mass estimate of 0.803 solar masses and a reported radius estimate of 0.77 solar radii, and has a reported temperature of 5420 K. Its mass and radius estimates are smaller than the Sun's, and its temperature is cooler than the Sun's.

Kepler-37 b is a Sub-Earth, a size class for planets smaller than Earth. It was discovered in 2013 and has a reported upper limit of 0.79 Earth masses, an orbital period of 13.4 days, and a reported radius estimate of 0.31 Earth radii, smaller than Earth's. Kepler-37 c, also a Sub-Earth discovered in 2013, has a reported upper limit of 1.3 Earth masses, an orbital period of 21.3 days, and a reported radius estimate of 0.755 Earth radii, smaller than Earth's.

Kepler-37 d is a Super-Earth, a size class reaching 2.5 times Earth's radius. Discovered in 2013, it has a reported upper limit of 2 Earth masses, an orbital period of 39.8 days, and a reported radius estimate of 2.03 Earth radii, larger than Earth's. Kepler-37 e was discovered in 2014 and has an orbital period of 51.2 days; no radius or mass is reported for it. Among the listed planets, Kepler-37 b has the shortest year by reported estimates, at 13.4 days, and Kepler-37 e has the longest, at 51.2 days.