The Origin of Jupiter’s Obliquity

Abstract

The origin of the 3.°12 obliquity of Jupiter’s spin axis to its orbit normal is unknown. Improved estimates of Jupiter’s moment of inertia rule out a previously proposed explanation involving a resonance with the precession of the inclined orbit of Uranus. We find that a nonadiabatic crossing of the resonance between Jupiter’s spin precession and the −f 5 + f 6 + g 6 mode could have tilted Jupiter to its present-day obliquity starting from a 0° primordial obliquity. This places constraints on the migration rates of the satellites Ganymede and Callisto.