Kepler-37d

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

A 2021 study detected Kepler-37d via radial velocity, finding a mass of about, but a 2023 study instead found an upper limit on its mass of only. 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 238900 mi away.

Host star
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 and a radius of 0.79. It has a temperature of 5417 K and is 5.66 billion years old. In comparison, the Sun is 4.6 billion years old, and has a temperature of 5778 K.

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.