Kepler-538 is a Sun-like G-type star (about 0.89 solar masses, 5,534 K, 0.87 solar radii), 156 light-years from Earth. Kepler-538 b is a 12.9-Earth-mass planet, with an orbital period of 81.7 days, at 0.355 AU from its star, and an equilibrium temperature near 417 K, on an eccentric orbit (e ≈ 0.21), discovered in 2016 via transit. The planet was found when it crossed the face of its star, producing periodic dips in brightness that reveal its size and orbital period to space-based photometry. The planet's marked eccentricity suggests past scattering events or perturbations from unseen companions.