CD Cet is a cool M-dwarf (about 0.16 solar masses, 3,130 K, 0.17 solar radii), 8.6 light-years from Earth. CD Cet b is a 4.0-Earth-mass planet, with an orbital period of 2.3 days, at 0.018 AU from its star, and an equilibrium temperature near 464 K, 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. CD Cet b skims its star closer than Mercury orbits the Sun.