GJ 1214 is a cool M-dwarf (about 0.18 solar masses, 3,101 K, 0.22 solar radii), 48 light-years from Earth. GJ 1214 b is the archetype sub-Neptune, a nearby mini-Neptune whose flat transmission spectrum hides a high-metallicity or hazy atmosphere. GJ 1214 b is a 8.4-Earth-mass planet, with an orbital period of 1.6 days, at 0.015 AU from its star, and an equilibrium temperature near 567 K, discovered in 2009 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. GJ 1214 b skims its star closer than Mercury orbits the Sun.