Kepler-338 and Its Four Planets

Kepler-338 is a star 1800 light-years away with four planets. The host star is 4.79 billion years old, has a reported mass estimate larger than the Sun's at 1.2 solar masses, a reported radius estimate larger than the Sun's at 1.78 solar radii, and a reported temperature hotter than the Sun's at 6000 K.

All four planets were discovered in 2014 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-338 b is a Super-Earth with a radius of 2.44 Earth radii, larger than Earth's, and an orbital period of 13.7 days, the second-shortest among the listed planets. Kepler-338 c is a Super-Earth with a radius of 2.34 Earth radii, larger than Earth's, and an orbital period of 24.3 days, the second-longest among the listed planets. Kepler-338 d is Neptune-like, with a radius of 3 Earth radii, larger than Earth's, and an orbital period of 44.4 days, the longest among the listed planets.

Kepler-338 e is a Super-Earth with a radius of 1.56 Earth radii, the smallest of the four and larger than Earth's, and an ordinary mass of 8.5 Earth masses, also larger than Earth's. Its mean density is 12.3 g/cm³, 2.24 times Earth's, and its orbital period of 9.34 days is the shortest among the listed planets.

Size classifications compare radius with Earth's: a Super-Earth reaches 2.5 times Earth's radius, while a Neptune-like planet reaches 4 times. An orbital period is the time a planet takes to complete one orbit: its year.