 55 Cancri b was discovered in 1996 by Geoffrey Marcy and R. Paul Butler . It was the fourth known extrasolar planet , excluding pulsar planets . Like the majority of known extrasolar planets , it was discovered by detecting variations in its star 's radial velocity caused by the planet 's gravity . By making sensitive measurements of the Doppler shift of the spectrum of 55 Cancri A , a 15 @-@ day periodicity was detected . The planet was announced in 1996 , together with the planet of Tau Boötis and the innermost planet of Upsilon Andromedae . 
