GJ 180: A Nearby Red Dwarf and Its Three Known Planets

GJ 180 is an M2 star located 38.9 light-years from Earth. Its reported mass is 0.406 solar masses, its reported radius is 0.413 solar radii, and its reported temperature is 3560 K. Each of these estimates is smaller or cooler than the corresponding value for the Sun. Three planets have been identified around this host.

GJ 180 b and GJ 180 c were both discovered in 2014 using the radial velocity method, which detects the gravitational wobble a planet induces in its star's motion. GJ 180 b has a minimum mass of 6.49 Earth masses and an orbital period of 17.1 days, the shortest year among the listed planets. GJ 180 c has a minimum mass of 6.4 Earth masses and an orbital period of 24.3 days, the second-shortest year among the listed planets. Its minimum mass is the smallest of the three. Both minimum masses are larger than Earth's.

GJ 180 d was discovered in 2020, also by radial velocity. Its minimum mass is 7.56 Earth masses, the largest among the listed planets, and also larger than Earth's. Its orbital period is 106 days, the longest year among the listed planets. A minimum mass is a lower bound on a planet's true mass, distinct from an ordinary mass estimate. In every case, the reported values represent lower limits rather than exact figures.