About this world
HD 180617 b is a sub-Neptune orbiting HD 180617, a cool red dwarf (type M2.5V) 19.3 light-years from Earth. It is about 3.5 times the size of Earth (its size estimated from its mass), with at least 12 Earth masses (a minimum, measured by radial velocity). It completes an orbit every 106 days at 0.34 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 202 K (−71 °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 2018 by radial velocity with Calar Alto Observatory. The star wobbles toward and away from us, Doppler-shifting its spectrum.