The M-Dwarf GJ 3378 and Its Single Known Planet

GJ 3378 is an M4 V star, a small, cool red dwarf, located 25.2 light-years from us. Its spectral class indicates a main-sequence star, and its measured properties reinforce that picture: it has 0.262 solar masses, 0.275 solar radii, and a temperature of 3340 K. Each of these is smaller or cooler than the corresponding solar value.

One planet has been found around GJ 3378. Named GJ 3378 b, it was detected in 2026 through the radial velocity method, which measures the wobble a planet's gravity induces in its star's motion; repeated wobbles reveal the planet and its orbital period. The planet has a minimum mass of 2.3 Earth masses, larger than Earth's, meaning this is only a lower bound on its true mass. GJ 3378 b orbits its star every 21.5 days.