55 Cancri

55 Cancri (abbreviated 55 Cnc) is a binary star located around 40 light-years away in the constellation Cancer. It has the Bayer designation Rho1 Cancri. The system contains a yellow dwarf star (55 Cancri A) similar to our Sun and a red dwarf (55 Cancri B). The two components are separated by over 1000 times the distance from the Earth to the Sun.

As of 2004, four extrasolar planets are known in orbit around 55 Cancri A. Three of the planets are comparable to Jupiter in mass, while the innermost planet has a mass similar to that of Neptune. The 55 Cancri system was the first known four-planet extrasolar planetary system.

55 Cancri A is ranked 63rd in the list of top 100 target stars for the NASA Terrestrial Planet Finder mission.

(Note: "55 Cancri" is seen more often than "Rho1 Cancri", although the Bayer designation is used by those who feel that they trump Flamsteed numbers in preference. As a matter of fact, they usually do -- Tau Bootis is almost never called "4 Bootis" -- but in this case the superscript in "Rho1" makes the Bayer designation rather cumbersome to use, making "55 Cancri" the more commonly-used name for the star.)