The tilt of Saturn’s spin axis to its orbit plane is 26N7, while that of Jupiter is only 3N1. We offer an explanation for this puzzling difference owing to gravitational perturbations of Saturn by the planet Neptune. A similarity between the precession period of Saturn’s spin axis and the 1:87 ; 10 yr precession period of Neptune’s slightly inclined orbit plane implicates a resonant interaction...

We argue that the gas giants Jupiter and Saturn were both formed with their rotation axes nearly perpendicular to their orbital planes, and that the large current tilt of the ringed planet was acquired in a post-formation event. We identify the responsible mechanism as trapping into a secular spin-orbit resonance that couples the angular momentum of Saturn’s rotation to that of Neptune’s orbit....