HAT-P-9 is a Sun-like F-type star (about 1.28 solar masses, 6,350 K, 1.34 solar radii), 455 light-years from Earth. HAT-P-9 b is a 0.75-Jupiter-mass companion, with an orbital period of 3.9 days, at 0.053 AU from its star, and an equilibrium temperature near 1,540 K, on an eccentric orbit (e ≈ 0.08), discovered in 2008 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.