An Exploration of Double Diffusive Convection in Jupiter as a Result of Hydrogen-Helium Phase Separation

TL;DR

This paper develops a self-consistent model of Jupiter's internal structure considering helium phase separation and double diffusive convection, revealing the rarity of such models and implications for Jupiter's thermal evolution.

Contribution

It introduces a framework for modeling Jupiter's interior with helium rain and explores the effects of layered convection on its thermal evolution, based on recent simulations.

Findings

Self-consistent models with helium rain are rare.

Layer heights of 0.1-1 km are needed to match Jupiter's luminosity.

No models with oscillatory double diffusive convection were found.

Abstract

Jupiter's atmosphere has been observed to be depleted in helium (Yatm~0.24), suggesting active helium sedimentation in the interior. This is accounted for in standard Jupiter structure and evolution models through the assumption of an outer, He-depleted envelope that is separated from the He-enriched deep interior by a sharp boundary. Here we aim to develop a model for Jupiter's inhomogeneous thermal evolution that relies on a more self-consistent description of the internal profiles of He abundance, temperature, and heat flux. We make use of recent numerical simulations on H/He demixing, and on layered (LDD) and oscillatory (ODD) double diffusive convection, and assume an idealized planet model composed of a H/He envelope and a massive core. A general framework for the construction of interior models with He rain is described. Despite, or perhaps because of, our simplifications made we find that self-consistent models are rare. For instance, no model for ODD convection is found. We modify the H/He phase diagram of Lorenzen et al. to reproduce Jupiter's atmospheric helium abundance and examine evolution models as a function of the LDD layer height, from those that prolong Jupiter's cooling time to those that actually shorten it. Resulting models that meet the luminosity constraint have layer heights of about 0.1-1 km, corresponding to ~10,-20,000 layers in the rain zone between ~1 and 3-4.5 Mbars. Present limitations and directions for future work are discussed, such as the formation and sinking of He droplets.