HATS-51 is a Sun-like G-type star (about 1.19 solar masses, 5,758 K, 1.44 solar radii), 390 light-years from Earth. HATS-51 b is a 0.77-Jupiter-mass companion, with an orbital period of 3.3 days, at 0.046 AU from its star, and an equilibrium temperature near 1,553 K, on an eccentric orbit (e ≈ 0.33), discovered in 2017 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.