Spin Dynamics of Extrasolar Giant Planets in Planet–Planet Scattering

Abstract

Abstract Planet–planet scattering best explains the eccentricity distribution of extrasolar giant planets, and past literature showed that the orbits of planets evolve due to planet–planet scattering. This work studies the spin evolution of planets in planet–planet scattering in two-planet systems. Spin can evolve dramatically due to spin–orbit coupling made possible by the evolving spin and orbital precession during the planet–planet scattering phase. The main source of torque to planet spin is the stellar torque, and the planet–planet torque contribution is negligible. As a consequence of the evolution of the spin, planets can end up with appreciable obliquities (the angle between a planet’s own orbit normal and spin axis), with the obliquity distribution peaking at about 10°, and extending to much larger values.