HAT-P-54 is an orange K-type dwarf (about 0.65 solar masses, 4,390 K, 0.62 solar radii), 144 light-years from Earth. HAT-P-54 b is a 0.76-Jupiter-mass companion, with an orbital period of 3.8 days, at 0.041 AU from its star, and an equilibrium temperature near 818 K, on an eccentric orbit (e ≈ 0.07), discovered in 2015 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.