The M-Dwarf 55 Cnc B and Its Two Known Planets

55 Cnc B is an M4.5 V star, a small, cool red dwarf, located 40.7 light-years away. Its reported mass is 0.26 solar masses and its reported radius is 0.274 solar radii, both smaller than the Sun's, while its reported temperature of 3290 K is cooler than the Sun's. The star's age is given as a reported lower limit of 10 billion years. Two planets are known to orbit this host.

55 Cnc B b and 55 Cnc B c were both discovered in 2025 by the radial velocity method, which detects the wobble a planet's gravity induces in its star's motion. Each planet has a minimum mass: 3.5 Earth masses for 55 Cnc B b and 5.3 Earth masses for 55 Cnc B c, both larger than Earth's minimum-mass value. Minimum mass is a lower bound on a planet's true mass, distinct from an ordinary mass estimate.

The two planets differ in their years. 55 Cnc B b completes one orbit in 6.8 days, the shortest period among the listed planets, while 55 Cnc B c takes 33.7 days, the longest among them.