LHS 3154 is a cool M-dwarf (about 0.11 solar masses, 2,861 K, 0.14 solar radii), 15.8 light-years from Earth. LHS 3154 b is a 13.2-Earth-mass planet, with an orbital period of 3.7 days, at 0.023 AU from its star, on an eccentric orbit (e ≈ 0.08), discovered in 2023 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. LHS 3154 b skims its star closer than Mercury orbits the Sun.