TrES-4 is a Sun-like F-type star (about 1.08 solar masses, 6,200 K, 1.66 solar radii), 516 light-years from Earth. TrES-4 b is a 0.78-Jupiter-mass companion, with an orbital period of 3.6 days, discovered in 2007 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. The planet's large radius (18.0 Earth radii) indicates a bloated atmosphere heated by intense stellar radiation.