WASP-21 is a Sun-like G-type star (about 1.01 solar masses, 5,800 K), 258 light-years from Earth. WASP-21 b is a 0.30-Jupiter-mass companion, with an orbital period of 4.3 days, at 0.052 AU from its star, discovered in 2010 via transit. The planet was found when it crossed the face of its star, producing periodic dips in brightness that reveal its size and orbital period to space-based photometry. WASP-21 b orbits well inside Earth's distance from the Sun. The planet's large radius (12.0 Earth radii) indicates a bloated atmosphere heated by intense stellar radiation.