GJ 251 and Its Two Known Planets

GJ 251 is a small, cool star 18.2 light-years away with an M3.0V spectral type, meaning it is a red dwarf. Its mass is 0.35 solar masses, its radius is 0.36 solar radii, and its temperature is 3340 K. The star is estimated to be 6.8 billion years old. Two planets are known to orbit it.

Both planets were found using the radial velocity method, which detects the wobble a planet's gravity induces in its star's motion. GJ 251 b, discovered in 2020, has a minimum mass of 3.85 Earth masses and an orbital period of 14.2 days. GJ 251 c, discovered in 2025, has a minimum mass of 3.88 Earth masses and an orbital period of 53.6 days. Minimum mass is a lower bound on a planet's true mass, not an ordinary mass estimate, so each planet's actual mass is at least the stated value. Both planets' minimum masses are larger than Earth's. Among the listed planets, GJ 251 b has the shortest year and the smallest minimum mass, while GJ 251 c has the longest year and the largest minimum mass.