HATS-31 is a Sun-like F-type star (about 1.27 solar masses, 6,050 K, 1.87 solar radii), 774 light-years from Earth. HATS-31 b is a 0.88-Jupiter-mass companion, with an orbital period of 3.4 days, at 0.048 AU from its star, and an equilibrium temperature near 1,823 K, on an eccentric orbit (e ≈ 0.23), discovered in 2016 via transit. The inner world is a hot Jupiter — a gas giant hugging its star at a fraction of Mercury's distance — a class that forced astronomers to rethink how giant planets form and migrate inward.