K2-233 and Its Three Planets

K2-233 is a K3 star located 220 light-years away. It is 0.36 billion years old, with a mass of 0.8 solar masses, a radius of 0.745 solar radii, and a temperature of 4950 K. The star’s reported mass and radius estimates are smaller than the Sun’s, and its reported temperature is cooler than the Sun’s. Three planets orbit this host.

K2-233 b, K2-233 c, and K2-233 d were all discovered by transit in 2018. K2-233 b is an Earth-like planet with a mass of 2.4 Earth masses, a radius of 1.32 Earth radii, and an orbital period of 2.47 days. Its mean density is 5.82 g/cm³, 1.06 times Earth's. K2-233 c is also Earth-like, with a mass of 4.6 Earth masses, a radius of 1.27 Earth radii, and an orbital period of 7.06 days. Its mean density is 12.3 g/cm³, 2.24 times Earth's. K2-233 d is a Super-Earth with a mass of 10.3 Earth masses, a radius of 2.36 Earth radii, and an orbital period of 24.4 days. Its mean density is 4.3 g/cm³, 0.781 times Earth's.

Among the listed planets, K2-233 b has the shortest year by reported estimates, K2-233 c has the second-shortest year by reported estimates, and K2-233 d has the longest year by reported estimates. K2-233 c has the smallest radius by reported estimates, K2-233 b has the second-smallest radius by reported estimates, and K2-233 d has the largest radius by reported estimates. K2-233 b has the smallest reported mass, K2-233 c has the second-smallest reported mass, and K2-233 d has the largest reported mass. The reported radius estimates for K2-233 b, K2-233 c, and K2-233 d are all larger than Earth’s, and the reported mass estimates for all three are also larger than Earth’s.