HD 153557 and Its Three Worlds

HD 153557 is a K0 star located 58.5 light-years away. A spectral type of K0 places it in the cooler, redder part of the classification sequence that runs from M through K, G, F, and A, with the Sun being a G-type star. The star holds a reported mass of 0.73 solar masses, a radius of 0.84 solar radii, and a temperature of 4650 K. Its reported mass estimate is smaller than the Sun's, its reported radius estimate is smaller than the Sun's, and its reported temperature is cooler than the Sun's. Three planets are known to orbit this host.

HD 153557 b was discovered in 2022 by the radial velocity method, which detects the wobble a planet's gravity induces in its star's motion. It has a minimum mass of 20.3 Earth masses, a lower bound on its true mass, and an orbital period of 7.3 days. Among the listed planets, it has the shortest year by reported estimates. HD 153557 c, also found in 2022 by radial velocity, carries a minimum mass of 17.5 Earth masses, larger than Earth's, and completes an orbit in 15.3 days. Among the listed planets, it has the second-shortest year by reported estimates.

HD 153557 d has a reported orbital period of 40700 days. Its ordinary mass estimate is 8730 Earth masses, a figure larger than Earth's and roughly 27.5 times Jupiter's mass. Among the listed planets, it has the longest year by reported estimates. Like its siblings, it was discovered in 2022 through radial velocity measurements.