The importance of gravity field spectrum for icy satellite interior structure determination: the case of Europa with the Europa Clipper mission

A better understanding of the interior structure of icy moons in our Solar System is necessary to answer fundamental questions about their formation, evolution, and habitability. Until now, insights on the interior layering, core structure, and density distribution have been solely derived from global-scale gravity measurements, such as the mass, the moment of inertia (from the degree-2 static gravity field and/or obliquity), and the tidal gravity response. With the upcoming NASA Europa Clipper and ESA JUICE missions, we will obtain reliable estimates of the gravity field of Jupiter’s icy moons to higher degrees (shorter wavelengths).

In this work, we present a new methodology and investigate the efficacy of utilizing the measured gravity field amplitude spectrum as an additional constraint in the inversion of the interior structure of differentiated icy bodies. After introducing and discussing the general methodology, we focus on Europa by considering the anticipated measurement accuracy of the Europa Clipper gravity and radio science investigation. We show that a Bayesian inversion of Europa’s interior that incorporates the measured gravity field spectrum offers much stronger determination of key geophysical parameters related to the interior structure of the body. In particular, it allows reliable constraints on the hydrosphere (ice shell and ocean) thickness, to within 10-20 km uncertainty, while at the same time reliably estimating key characteristics of the core, the silicate mantle, and the ocean floor, which is not possible with the traditional approach. The approach we present offers new sensitivity to the seafloor topography and elastic thickness, and it gives a way of probing the heat flow from the silicate interior. Ultimately, these fundamental constraints will help evaluate the potential for habitability of Europa and its subsurface ocean.

Updating our previous work (Cascioli et al., 2024), we augment the inverse problem with the expected tidal constraints that Europa Clipper will derive, and we assess their beneficial role on the interior structure determination.

 

Cascioli, G., et al. "Leveraging the Gravity Field Spectrum for Icy Satellite Interior Structure Determination: The Case of Europa with the Europa Clipper Mission." The Planetary Science Journal 5.2 (2024): 45.