HN Lib is a cool M-dwarf (about 0.29 solar masses, 3,347 K, 0.30 solar radii), 6.2 light-years from Earth. HN Lib b is a 5.5-Earth-mass planet, with an orbital period of 36.1 days, at 0.142 AU from its star, and an equilibrium temperature near 234 K, 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.