K2-31 is a Sun-like G-type star (about 0.91 solar masses, 5,280 K, 0.78 solar radii), 111 light-years from Earth. K2-31 b is a 1.77-Jupiter-mass companion, with an orbital period of 1.3 days, at 0.022 AU from its star, discovered in 2016 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. K2-31 b skims its star closer than Mercury orbits the Sun.