WASP-13 is a Sun-like G-type star (about 0.72 solar masses, 5,950 K, 1.37 solar radii), 228 light-years from Earth. WASP-13 b is a 0.36-Jupiter-mass companion, with an orbital period of 4.4 days, discovered in 2009 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 (13.7 Earth radii) indicates a bloated atmosphere heated by intense stellar radiation.