WASP-81 is a Sun-like G-type star (about 1.08 solar masses, 5,870 K, 1.28 solar radii), 399 light-years from Earth. WASP-81 b is a 0.73-Jupiter-mass companion, with an orbital period of 2.7 days, at 0.039 AU from its star, and an equilibrium temperature near 1,623 K, on an eccentric orbit (e ≈ 0.07), 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.