WASP-39 is a Sun-like G-type star (about 0.91 solar masses, 5,485 K, 0.94 solar radii), 214 light-years from Earth. WASP-39 b was the benchmark target for JWST's first exoplanet atmosphere results, including water, carbon dioxide, and sulfur dioxide. WASP-39 b is a 0.28-Jupiter-mass companion, with an orbital period of 4.1 days, at 0.048 AU from its star, and an equilibrium temperature near 1,166 K, discovered in 2011 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-39 b skims its star closer than Mercury orbits the Sun.