Convection and Mixing in Giant Planet Evolution

TL;DR

This paper presents a self-consistent model of heat and material convection in giant planets, revealing how initial composition and internal structure influence their evolution and challenging the assumption of homogeneity.

Contribution

It introduces the first self-consistent calculations of convective transport of heat and material in evolving giant planets, considering various initial conditions and mixing efficiencies.

Findings

Heavy-element cores are not eroded by convection with sharp compositional boundaries.

Outer envelopes become homogeneous if initial compositional gradients exist.

Mixing of injected heavy materials in convective envelopes is highly efficient.

Abstract

The primordial internal structures of gas giant planets are unknown. Often giant planets are modeled under the assumption that they are adiabatic, convective, and homogeneously mixed, but this is not necessarily correct. In this work, we present the first self-consistent calculation of convective transport of both heat and material as the planets evolve. We examine how planetary evolution depends on the initial composition and its distribution, whether the internal structure changes with time, and if so, how it affects the evolution. We consider various primordial distributions, different compositions, and different mixing efficiencies and follow the distribution of heavy elements in a Jupiter-mass planet as it evolves. We show that a heavy-element core cannot be eroded by convection if there is a sharp compositional change at the core-envelope boundary. If the heavy elements are initially distributed within the planet according to some compositional gradient, mixing occurs in the outer regions resulting in a compositionally homogeneous outer envelope. Mixing of heavy materials that are injected in a convective gaseous envelope are found to mix efficiently. Our work demonstrates that the primordial internal structure of a giant planet plays a substantial role in determining its long-term evolution and that giant planets can have non-adiabatic interiors. These results emphasize the importance of coupling formation, evolution, and internal structure models of giant planets self-consistently.