About this world
55 Cnc B b is a super-Earth orbiting 55 Cnc B, a cool red dwarf (type M4.5V) 40.7 light-years from Earth. It is about 1.7 times the size of Earth (its size estimated from its mass), with at least 3.5 Earth masses (a minimum, measured by radial velocity). It completes an orbit every 6.8 days at 0.044 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 395 K (122 °C): too cold for liquid water on its 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 c.