About this world
HD 128311 b is a gas giant orbiting HD 128311, an orange dwarf (type K0) 53.3 light-years from Earth. It is about 1.2 times the size of Jupiter (its size estimated from its mass), with at least 1.8 Jupiter masses (a minimum, measured by radial velocity). It completes an orbit every 453 days at 1.1 AU from its star, on a strongly elongated orbit (e = 0.3).
Its equilibrium temperature is about 200 K (−73 °C): too cold for liquid water on its surface. At its size it almost certainly keeps a deep envelope of hydrogen and helium.
It was discovered in 2002 by radial velocity with W. M. Keck Observatory. The star wobbles toward and away from us, Doppler-shifting its spectrum. HD 128311 has 2 known planets; the others are HD 128311 c.