HD 180617 is a cool M-dwarf (about 0.48 solar masses, 3,534 K, 0.48 solar radii), 5.9 light-years from Earth. HD 180617 b is a 12.2-Earth-mass planet, with an orbital period of 106 days, at 0.343 AU from its star, on an eccentric orbit (e ≈ 0.10), discovered in 2018 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.