Gl 378 is a cool M-dwarf (about 0.56 solar masses, 3,879 K, 0.56 solar radii), 15.0 light-years from Earth. Gl 378 b is a 13.0-Earth-mass planet, with an orbital period of 3.8 days, at 0.039 AU from its star, and an equilibrium temperature near 830 K, on an eccentric orbit (e ≈ 0.11), discovered in 2019 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.