XO-3 is a Sun-like F-type star (about 1.45 solar masses, 6,970 K, 1.52 solar radii), 213 light-years from Earth. XO-3 b is a massive hot Jupiter on a tilted, eccentric orbit, a sign that scattering rather than quiet migration put it there. XO-3 b is a 13.3-Jupiter-mass companion, with an orbital period of 3.2 days, at 0.048 AU from its star, and an equilibrium temperature near 1,890 K, on an eccentric orbit (e ≈ 0.28), discovered in 2007 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.