HD 217107 b is an extrasolar planet[2] approximately 65 light-years away from Earth in the constellation of Pisces (the Fish).
It was found by detecting small variations in the radial velocity of the star it orbits, caused by the tug of its gravity.
A study of the radial velocity of HD 217107 carried out in 1998 revealed that its motion along the line of sight varied over a 7.1 day cycle.
The period and amplitude of this variation indicated that it was caused by a planetary companion in orbit around the star, with a minimum mass slightly greater than that of Jupiter.
While most planets with orbital periods of less than 10 days have almost circular orbits, HD 217107 b has a somewhat eccentric orbit, and its discoverers hypothesized that this could be due to the gravitational influence of a second planet in the system at a distance of several astronomical units (AU).