M ar 2 00 8 Orbital Dynamics Of A Second Planet In HD 17156

In this letter we report the possible existence of a second planet in the transiting extrasolar planet system HD17156 and its interactive dynamics with the previously known planet. The analysis is achieved through the POFP optimization software which is based on a full integration of the system’s multiple-body Newtonian equations of motion. The two-planet solution yields a significantly improved fit to the previously published radial velocities. The two planets are strongly interacting and exchange angular momentum, yet remain stable as they mutually excite orbital eccentricities and periastron advances. Subject headings: planetary systems – celestial mechanics – gravitation – instabilities – methods: N-body simulations – methods: numerical