GJ 338 B is a cool M-dwarf (about 0.64 solar masses, 4,014 K, 0.58 solar radii), 6.3 light-years from Earth. GJ 338 B b is a 10.6-Earth-mass planet, with an orbital period of 24.4 days, at 0.142 AU from its star, on an eccentric orbit (e ≈ 0.11), discovered in 2020 via radial velocity. The planet betrayed itself through the star's reflex motion — a technique that first revealed worlds around Sun-like stars in the 1990s and remains a workhorse of exoplanet discovery. The planet's marked eccentricity suggests past scattering events or perturbations from unseen companions.