Tilting Jupiter (a bit) and Saturn (a lot) During Planetary Migration

الأصل · EN

We study the effects of planetary late migration on the gas giants obliquities. We consider the planetary instability models from Nesvorny & Morbidelli (2012), in which the obliquities of Jupiter and Saturn can be excited when the spin-orbit resonances occur. The most notable resonances occur when the s₇ and s₈ frequencies, changing as a result of planetary migration, become commensurate with the precession frequencies of Jupiter's and Saturn's spin vectors. We show that Jupiter may have obtained its present obliquity by crossing of the s₈ resonance. This would set strict constrains on the character of migration during the early stage. Additional effects on Jupiter's obliquity are expected during the last gasp of migration when the s₇ resonance was approached. The magnitude of these effects depends on the precise value of the Jupiter's precession constant. Saturn's large obliquity was likely excited by capture into the s₈ resonance. This probably happened during the late stage of planetary migration when the evolution of the s₈ frequency was very slow, and the conditions for capture into the spin-orbit resonance with s₈ were satisfied. However, whether or not Saturn is in the spin-orbit resonance with s₈ at the present time is not clear, because the existing observations of Saturn's spin precession and internal structure models have significant uncertainties.