Dynamical tides in Jupiter as revealed by Juno

TL;DR

Juno's precise gravity measurements reveal a non-hydrostatic tidal response in Jupiter, which we interpret as the gravitational effect of dynamical tides, marking the first such detection in a gas giant.

Contribution

This study models Jupiter's dynamical tides using perturbation theory and simple interior models, explaining the observed deviation in Love number $k_2$ as a dynamical tide effect.

Findings

Dynamical tides cause a -4% correction to Jupiter's Love number $k_2$.

The correction aligns with Juno's measurements, confirming dynamical tides' gravitational influence.

Results support the detection of dynamical tides in a gas giant, aiding future interior structure analysis.

Abstract

The Juno orbiter continues to collect data on Jupiter's gravity field with unprecedented precision since 2016, recently reporting a non-hydrostatic component in the tidal response of the planet. At the mid-mission perijove 17, Juno registered a Love number $k_2=0.565\pm0.006$ that is $-4\pm1\%$ ($1\sigma$) 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 $\Delta k_2$ 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 $\Delta k_2$ observed by Juno. By simplifying Jupiter's interior into a core-less, fully-convective, and chemically-homogeneous body, we calculate $\Delta k_2$ in a model following an $n=1$ polytrope equation of state. Our numerical results for the $n=1$ polytrope qualitatively follow the behaviour 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 $\Delta k_2=-4\pm1\%$, in agreement with the non-hydrostatic 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.