TrES-1 is a Sun-like G-type star (about 1.04 solar masses, 5,230 K, 0.85 solar radii), 160 light-years from Earth. TrES-1 b is a 0.84-Jupiter-mass companion, with an orbital period of 3.0 days, discovered in 2004 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 (12.7 Earth radii) indicates a bloated atmosphere heated by intense stellar radiation.