An Energy Perspective of Core Erosion in Gas Giant Planets

TL;DR

This paper investigates the energy requirements for eroding heavy element cores in gas giants like Jupiter and Saturn, considering different scenarios and their implications for core survival over billions of years.

Contribution

It provides a quantitative analysis of the energy needed to erode planetary cores, highlighting the dependence on initial conditions and offering insights into core longevity.

Findings

Jupiter can erode a fuzzy core by up to ~10 Earth masses under certain energy assumptions.

Saturn's core is more resistant, with minimal erosion expected.

Core erosion depends strongly on initial temperature and entropy profiles.

Abstract

Juno and Cassini have shown that Jupiter and Saturn likely contain extended gradients of heavy elements. Yet, how these gradients can survive over billions of years remains an open question. Classical convection theories predict rapid mixing and homogenization, which would erase such gradients on timescales far shorter than the planets' ages. To address this, we estimate the energy required to erode both dense and fuzzy cores, and compare it to what the planet can realistically supply. If the entire cooling budget is available to drive mixing, then even a compact core can, in principle, be destroyed. But if mixing is limited to the thermal energy near the core, which is another plausible scenario, the energy falls short. In that case, Jupiter can erode a fuzzy core by up to approximately $10~\mearth$, but a compact one remains intact. Saturn's core is more robust. Even in the fuzzy case, only about $1~\mearth$ is lost, and if the core is compact, erosion is negligible. The outcome depends sensitively on the assumed initial temperature and entropy profiles. Hotter and more superadiabatic interiors are more prone to mixing. We suggest that 3D simulations of convection driven from above, with realistic stratification and enough depth (i.e., many density scale heights) would be of great interest to further constrain the energy budget for core erosion.