HATS-39 is a Sun-like F-type star (about 1.38 solar masses, 6,572 K, 1.62 solar radii), 879 light-years from Earth. HATS-39 b is a 0.63-Jupiter-mass companion, with an orbital period of 4.6 days, at 0.060 AU from its star, and an equilibrium temperature near 1,645 K, on an eccentric orbit (e ≈ 0.28), discovered in 2018 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.