Dynamical tides in the Jovian System as revealed by Juno

Abstract:

Seismology has been a successful discipline in revealing the interior structure of many compact bodies such as Earth, Saturn, the Sun and even other distant stars. Yet, Jupiter, the most massive planet in the Solar System, remains opaque to seismological techniques as it does not have the optically thick rings that Saturn has nor the luminosity required for asteroseismology. In the absence of seismological constraints, the gravitational signature of global-scale motions allows for the following promising alternative. Since 2016, the Juno orbiter has been collecting data on Jupiter’s gravity field with unprecedented precision, recently detecting a 3-sigma non-hydrostatic component in the tidal response of the planet to the gravitational pull from Io. Here we evaluate if Jupiter is capable of producing a dynamical tide whose amplitude is detectable by Juno. Ultimately, we are interested on using the information contained in the amplitude of the dynamical tide to inform answers to fundamental questions about the origin and evolution of Jupiter: Does Jupiter have a core? What is the extension of Jupiter’s core? Is Jupiter’s core solid or diluted? Our analysis is based on estimating corrections to the hydrostatic k₂ using a theory of linear and small perturbations. We evaluate corrections to the hydrostatic k₂ from the dynamical tide in a planetary model with a fully-convective interior, an interior with a convective envelope overlapping an evanescent central region, and an interior with a dilute core represented by a stratified region with static stability. Each correction is calculated using simple theoretical models of planetary interiors. Preliminary results show that the gravitational pull from Io leads to a dynamical tide with a correction to k₂ comparable to the non-hydrostatic signal detected by Juno. These preliminary results suggest that Juno may have obtained the first clear detection of dynamical tides ever made in a gas giant planet.