HAT-P-66 is a Sun-like G-type star (about 1.25 solar masses, 6,002 K, 1.88 solar radii), 935 light-years from Earth. HAT-P-66 b is a 0.78-Jupiter-mass companion, with an orbital period of 3.0 days, at 0.044 AU from its star, and an equilibrium temperature near 1,896 K, on an eccentric orbit (e ≈ 0.09), 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.