Abstract
Abstract The Juno orbiter has continued to collect data on Jupiter's gravity field with unprecedented precision since 2016, recently reporting a nonhydrostatic component in the tidal response of the planet. At the mid-mission perijove 17, Juno registered a Love number k 2 = 0.565 ± 0.006 that is −4% ± 1% (1σ) from the theoretical hydrostatic k 2 ( hs ) = 0.590 . Here we assess whether the aforementioned departure of tides from hydrostatic equilibrium represents the neglected gravitational contribution of dynamical tides. We employ perturbation theory and simple tidal models to calculate a fractional dynamical correction Δk 2 to the well-known hydrostatic k 2. Exploiting the analytical simplicity of a toy uniform-density model, we show how the Coriolis acceleration motivates the negative sign in the Δk 2 observed by Juno. By simplifying Jupiter’s interior into a coreless, fully convective, and chemically homogeneous body, we calculate Δk 2 in a model following an n = 1 polytrope equation of state. Our numerical results for the n = 1 polytrope qualitatively follow the behavior of the uniform-density model, mostly because the main component of the tidal flow is similar in each case. Our results indicate that the gravitational effect of the Io-induced dynamical tide leads to Δk 2 = − 4% ± 1%, in agreement with the nonhydrostatic component reported by Juno. Consequently, our results suggest that Juno obtained the first unambiguous detection of the gravitational effect of dynamical tides in a gas giant planet. These results facilitate a future interpretation of Juno tidal gravity data with the purpose of elucidating the existence of a dilute core in Jupiter.
Highlights
The interior structure of a planet or star closely corresponds with its origin and evolution story
Our tidal models suggest that the gravity field observed by Juno captured the dynamical tidal response of Jupiter to the gravitational pull of the Galilean satellites
We show that two effects contribute to the dynamical gravity field of tides in Jupiter: the dynamical response of f-modes and the Coriolis acceleration
Summary
The interior structure of a planet or star closely corresponds with its origin and evolution story. Seismology provides the tightest constraints on the interior structure of Earth (Dahlen & Tromp (1998) and ref. Unlike Saturn, Jupiter lacks extensive optically-thick rings with embedded waves that are excited by resonance of ring particle motions with internal normal modes. To ring seismology, Doppler imaging reveals a suggested seismic behavior in Jupiter, limited to radial overtones of pmodes. The current Doppler imaging data resolves the spacing in frequency space of low-order p-modes, providing a loose constraint compatible with simple interior models (Gaulme et al 2011). Future efforts based on similar techniques promise revealing additional information on Jupiter’s seismic behavior. In the current absence of detailed seismological constraints, the Juno orbiter (Bolton et al 2017) emerges as the alternative directed to reveal Jupiter’s interior by employing gravity field measurements of global-scale motions.
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