About this world
55 Cnc B c is a sub-Neptune orbiting 55 Cnc B, a cool red dwarf (type M4.5V) 40.7 light-years from Earth. It is about 2.2 times the size of Earth (its size estimated from its mass), with at least 5.3 Earth masses (a minimum, measured by radial velocity). It completes an orbit every 33.7 days at 0.13 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 230 K (−43 °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 2025 by radial velocity with Mauna Kea Observatory. The star wobbles toward and away from us, Doppler-shifting its spectrum. 55 Cnc B has 2 known planets; the others are 55 Cnc B b.