HD 40307 and Its Five Known Planets

HD 40307 is a K3V star located 42.2 light-years from Earth. Its reported mass is 0.74 solar masses, its radius is 0.72 solar radii, and its temperature is 4830 K, making it smaller, smaller in radius, and cooler than the Sun. The star is estimated to be 2.6 billion years old. Five planets are known to orbit this host.

All five planets were detected by the radial velocity method, which measures the wobble a planet's gravity induces in its star's motion. HD 40307 b, c, and d were announced in 2009, while HD 40307 f and g were announced in 2013. Each planet's minimum mass is a lower bound on its true mass. The minimum masses of all five planets are larger than Earth's.

HD 40307 b has a minimum mass of 4 Earth masses and an orbital period of 4.31 days, the shortest year among the listed planets. HD 40307 c has a minimum mass of 6.6 Earth masses and a period of 9.62 days, the second-shortest. HD 40307 d has a minimum mass of 9.5 Earth masses, the largest among the listed planets, and a period of 20.4 days. HD 40307 f has a minimum mass of 5.2 Earth masses, the second-smallest, and a period of 51.8 days, the second-longest. HD 40307 g has a minimum mass of 7.1 Earth masses, the second-largest, and a period of 198 days, the longest among the listed planets.