HD 2638 is an orange K-type dwarf (about 0.77 solar masses, 5,186 K, 0.94 solar radii), 55.0 light-years from Earth. HD 2638 b is a 0.42-Jupiter-mass companion, with an orbital period of 3.4 days, at 0.040 AU from its star, discovered in 2005 via radial velocity. 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. HD 2638 b skims its star closer than Mercury orbits the Sun.