tau Boo is a Sun-like F-type star (about 1.32 solar masses, 6,466 K, 1.43 solar radii), 15.7 light-years from Earth. tau Boo b is a 4.32-Jupiter-mass companion, with an orbital period of 3.3 days, at 0.049 AU from its star, discovered in 1996 via radial velocity. 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. tau Boo b skims its star closer than Mercury orbits the Sun.