Kepler-37d is an exoplanet discovered by the Kepler space telescope in February 2013.^[4] It is located 209 light years away,^[5] in the constellation Lyra.^[4] With an orbital period of 39.8 days,^[3] it is the largest of the three known planets orbiting its parent star Kepler-37.^[6]

A 2021 study detected Kepler-37d via radial velocity, finding a mass of about 5.4 M_E,^[3] but a 2023 study instead found an upper limit on its mass of only 2 M_E.^[2] In either case, it is not a rocky planet, but a low-density planet rich in volatiles.

In 2015, a grant was approved to further expand the Sagan Planet Walk by installing a Kepler-37d station on the Moon 384,500 kilometers (238,900 mi) away.^[7][8]

The planet orbits a (G-type) star similar to the Sun, named Kepler-37, orbited by a total of four planets. The star has a mass of 0.80 M_☉ and a radius of 0.79 R_☉. It has a temperature of 5417 K and is 5.66 billion years old. In comparison, the Sun is 4.6 billion years old,^[9] and has a temperature of 5778 K.^[10]

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 9.71. Therefore, it is too dim to be seen with the naked eye.

• List of planets discovered by the Kepler spacecraft