WASP-31 is a Sun-like F-type star (about 1.16 solar masses, 6,302 K, 1.25 solar radii), 384 light-years from Earth. WASP-31 b is a 0.48-Jupiter-mass companion, with an orbital period of 3.4 days, at 0.047 AU from its star, discovered in 2010 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. WASP-31 b skims its star closer than Mercury orbits the Sun.