The gravitational imprint of an interior-orbital resonance in Jupiter-Io

Abstract

At mid-mission perijove 17, NASA's Juno mission has revealed a 7σ discrepancy between Jupiter's observed high-degree tidal response and the theoretical equilibrium tidal response, namely the Love number k₄₂. Here, we propose an interpretation for this puzzling disagreement based on an interior-orbital resonance between internal gravity waves trapped in Jupiter's dilute core and the orbital motion of Io. We use simple Jupiter models to calculate a fractional correction Δk₄₂ to the equilibrium tidal response that comes from the dynamical tidal response of a g-mode trapped in Jupiter's dilute core. Our results suggest that an extended dilute core (r≳0.7RJ) produces an interior-orbital resonance with Io that modifies Jupiter's tidal response in Δk₄₂ ∼ −11%, allowing us to fit Juno's k₄₂. In our proposed self-consistent scenario, Jupiter's dilute core evolves in resonant locking with Io's orbital migration, which allows the interior-orbital resonance to persist over geological timescales. This scenario requires a dilute core that becomes smoother or shrinks over time, together with a 24g1 mode (ℓ,m,n=4,2,1) with resonant tidal dissipation reaching Q₄ ∼ 1000. Jupiter's dilute core evolution path and the dissipation mechanism for the resonant ²₄g₁ mode are uncertain and motivate future analysis. No other alternative exists so far to explain the 7σ discrepancy in Juno k₄₂. Our proposed interior-orbital resonance can be tested by Juno observations of k₄₂ tides raised on Jupiter by Europa as obtained at the end of the extended mission (mid 2025), and by future seismological observations of Jupiter's ²₄g₁ mode oscillation frequency.