About this world
HD 181720 b is a gas giant orbiting HD 181720, a yellow, Sun-like star (type G1V) 196 light-years from Earth. It is about 1.2 times the size of Jupiter (its size estimated from its mass), with at least 0.4 Jupiter masses (a minimum, measured by radial velocity). It completes an orbit every 2.62 years at 1.9 AU from its star, on a strongly elongated orbit (e = 0.26).
Its equilibrium temperature is about 249 K (−24 °C), which places it in the conservative habitable zone: the band where liquid water could exist on a rocky surface. At its size it almost certainly keeps a deep envelope of hydrogen and helium.
It was discovered in 2009 by radial velocity with La Silla Observatory. The star wobbles toward and away from us, Doppler-shifting its spectrum.