HD 191939 and Its Six Planets

HD 191939 is a G8 V star located 175 light-years away. This Sun-like dwarf hosts six planets, and its reported mass, radius, and temperature are all smaller or cooler than the Sun's: it has 0.92 solar masses, 0.945 solar radii, and a temperature of 5430 K, with an age of 7 billion years.

The three Neptune-like planets were all found by the transit method in 2020. HD 191939 b has a mass of 10 Earth masses, a radius of 3.41 Earth radii, and an orbital period of 8.88 days, the shortest among the listed planets. HD 191939 c has 8 Earth masses, 3.2 Earth radii, and a period of 28.6 days, the second-shortest among the listed planets. HD 191939 d has 2.8 Earth masses, 3 Earth radii, and a period of 38.4 days. Each of these planets is larger and more massive than Earth, with estimated mean densities of 1.39, 1.35, and 0.574 g/cm³ respectively.

The remaining three planets were discovered by radial velocity in 2022. HD 191939 e has a minimum mass of 112 Earth masses and a period of 101 days. HD 191939 g has a minimum mass of 13.5 Earth masses and a period of 284 days, the second-longest among the listed planets. HD 191939 f has a minimum mass of 915 Earth masses and a period of 2900 days, the longest among the listed planets; its minimum mass is roughly 2.88 times Jupiter's mass. Each of these minimum masses is larger than Earth's, and because they are lower bounds, the true masses could be higher.