Kepler-78 is an orange K-type dwarf (about 0.78 solar masses, 5,058 K, 0.75 solar radii), 124 light-years from Earth. Kepler-78 b is an Earth-sized lava world with both mass and radius measured, on an 8.5-hour orbit. Kepler-78 b is a 1.7-Earth-mass planet, with an orbital period of 8.5 hours, at 0.009 AU from its star, and an equilibrium temperature near 2,223 K, discovered in 2013 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. Kepler-78 b skims its star closer than Mercury orbits the Sun.