The Interior Structure, Composition, and Evolution of Giant Planets

TL;DR

This paper reviews current knowledge on the interior structure, composition, and thermal evolution of giant planets, highlighting uncertainties, recent findings, and implications for both solar system and extrasolar planets.

Contribution

It provides an updated synthesis of interior models, discusses the impact of hydrogen equations of state, and reviews observational constraints from transiting and directly imaged exoplanets.

Findings

Jupiter's core mass uncertainty of 18 Earth masses due to hydrogen EOS variations

Deep envelope metallicities up to 0.95 in Uranus and Neptune suggest eroded cores

Many transiting exoplanets are larger than standard models predict, prompting new explanations.

Abstract

We discuss our current understanding of the interior structure and thermal evolution of giant planets. This includes the gas giants, such as Jupiter and Saturn, that are primarily composed of hydrogen and helium, as well as the "ice giants," such as Uranus and Neptune, which are primarily composed of elements heavier than H/He. The effect of different hydrogen equations of state (including new first-principles computations) on Jupiter's core mass and heavy element distribution is detailed. This variety of the hydrogen equations of state translate into an uncertainty in Jupiter's core mass of 18 M_Earth. For Uranus and Neptune we find deep envelope metallicities up to 0.95, perhaps indicating the existence of an eroded core, as also supported by their low luminosity. We discuss the results of simple cooling models of our solar system's planets, and show that more complex thermal evolution models may be necessary to understand their cooling history. We review how measurements of the masses and radii of the ~50 transiting extrasolar giant planets are changing our understanding of giant planets. In particular a fraction of these planets appear to be larger than can be accommodated by standard models of planetary contraction. We review the proposed explanations for the radii of these planets. We also discuss very young giant planets, which are being directly imaged with ground- and space-based telescopes.