Characterization of Icy Moon Hydrospheres Through Joint Inversion of Gravity and Magnetic Field Measurements

Abstract

Several bodies in the outer solar system are believed to host liquid water oceans underneath their icy surfaces. Knowledge of the hydrosphere properties is essential for understanding and assessing their habitability. We introduce a methodology based on Bayesian inference that enables a robust characterization of the hydrosphere through the combination of gravity and magnetic induction data. The interior models retrieved are consistent with the geophysical observations, leading to probability distributions for the relevant interior properties. We apply this joint inversion approach to constrain Europa's hydrosphere with gravity and magnetic field measurements acquired by the Galileo mission. Our results indicate that the combination of these datasets allows simultaneous constraints on the ice shell and ocean thickness, enhancing our knowledge of the hydrosphere structure. This methodology is valuable for synergistic interior science investigations of several missions in development or in planning, including Europa Clipper, JUICE and the Uranus Orbiter and Probe.

Leveraging the Gravity Field Spectrum for Icy Satellite Interior Structure Determination: The Case of Europa with the Europa Clipper Mission

“…This fact is particularly interesting considering that Europa Clipper will also measure the tidal response and magnetic field of the body. The tidal response (tidal potential and deformation combined) provides observability to the ice shell thickness and rigidity (Wahr et al 2006;Mazarico et al 2023), while the magnetic induction measurement provides sensitivity to the ocean thickness and to a lesser extent to the ice shell thickness (Biersteker et al 2023;Petricca et al 2023). Both these methods require some model assumptions.…”

Gravity Investigation to Characterize Enceladus's Ocean and Interior

“…This Bayesian inversion enables the exploration of the parameter space with the goal of matching the statistical distribution of the observations (e.g., mass, MoI, tidal Love number). Previous studies used this methodology to investigate the internal structure of celestial bodies (e.g., Khan et al 2007;Matsuyama et al 2016Genova et al 2019Drilleau et al 2021;Petricca et al 2023), enabling significant constraints from the deep interior to the outer shell.…”

“…To properly map the parameter space and to reduce the dependence of the inversion results on the initial model, 20 independent and distinct chains are generated. The convergence of the chains is tested with the Gelman-Rubin criterion (Gelman & Rubin 1992) by selecting a threshold for the potential scale reduction factor (PSRF) of 1.01 (for details see Petricca et al 2023). Each chain is iterated until ∼50,000 models are accepted.…”

Joint analysis of JUICE and Europa Clipper tracking data to study the Jovian system ephemerides and dissipative parameters

“…Therefore, the accuracy achievable on both Re(k 2 ) and Im(k 2 ) by JUICE and Europa Clipper may be sufficient to confirm the presence of a liquid ocean. However, a detailed characterization of the internal structure of Europa, including ocean density and ice shell thickness and rigidity, would require a global inversion of all available measurements, including tidal Love numbers k 2 and h 2 , static gravity field, topography, and magnetic induction (Wahr et al 2006;Durante et al 2019;Petricca et al 2023).…”