TOI-2109 is a Sun-like F-type star (about 1.45 solar masses, 6,540 K, 1.70 solar radii), 262 light-years from Earth. TOI-2109 b is one of the shortest-period giant planets known, an ultra-hot Jupiter orbiting in about 16 hours. TOI-2109 b is a 5.02-Jupiter-mass companion, with an orbital period of 16.1 hours, at 0.018 AU from its star, and an equilibrium temperature near 3,646 K, discovered in 2021 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.