CoRoT-21 is a Sun-like F-type star (about 1.29 solar masses, 6,200 K, 1.95 solar radii). CoRoT-21 b is a 2.26-Jupiter-mass companion, with an orbital period of 2.7 days, at 0.042 AU from its star, discovered in 2012 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. CoRoT-21 b skims its star closer than Mercury orbits the Sun.