HD 118203 and Its Two Worlds

HD 118203 is a K0 IV star located 301 light-years away. It is 5.25 billion years old and hosts two planets. Its reported mass is 1.22 solar masses, its radius is 2.03 solar radii, and its temperature is 5790 K. The star's reported mass estimate is larger than the Sun's, and its reported radius estimate is larger than the Sun's.

The first planet, HD 118203 b, was discovered in 2005 by the radial velocity method, which detects the wobble a planet's gravity induces in its star's motion. It is a Jupiter-like planet with a mass of 680 Earth masses and a radius of 12.8 Earth radii. Its orbital period is 6.13 days, and its mean density is 1.8 g/cm³, 0.326 times Earth's. Among the listed planets, HD 118203 b has the shortest year and the smallest reported mass.

The second planet, HD 118203 c, was discovered in 2024, also by radial velocity. It has a mass of 3750 Earth masses and an orbital period of 5100 days. Among the listed planets, HD 118203 c has the longest year and the largest reported mass.