About this world
HD 102117 b is a Neptune-like planet orbiting HD 102117, a yellow, Sun-like star (type G6V) 129 light-years from Earth. It is about 0.76 times the size of Jupiter (its size estimated from its mass), with at least 0.17 Jupiter masses (a minimum, measured by radial velocity). It completes an orbit every 20.8 days at 0.15 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 781 K (508 °C): far too hot for liquid water on its surface. At its size it almost certainly keeps a deep envelope of hydrogen and helium.
It was discovered in 2005 by radial velocity with La Silla Observatory. The star wobbles toward and away from us, Doppler-shifting its spectrum.