About this world
HN Lib b is a sub-Neptune orbiting HN Lib, a cool red dwarf (type M4.0V) 20.4 light-years from Earth. It is about 2.2 times the size of Earth (its size estimated from its mass), with at least 5.5 Earth masses (a minimum, measured by radial velocity). It completes an orbit every 36.1 days at 0.14 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 234 K (−39 °C), which places it in the conservative habitable zone: the band where liquid water could exist on a rocky surface. By the "cosmic shoreline", it has likely held on to an atmosphere.
It was discovered in 2023 by radial velocity with Calar Alto Observatory. The star wobbles toward and away from us, Doppler-shifting its spectrum.