Evolution of Jupiter and Saturn with helium rain

Abstract

Phase separation between hydrogen and helium at high pressures and temperatures leads to the rainout of helium in the deep interiors of Jupiter and Saturn. This process, also known as "helium rain", affects their long-term evolution. Therefore, modelling the evolution and internal structure of Jupiter and Saturn (and giant exoplanets) relies on the phase diagram of hydrogen and helium. In this work, we simulate the evolution of Jupiter and Saturn with helium rain by applying different phase diagrams of hydrogen and helium. We find that consistency between Jupiter s evolution and the Galileo measurement of its atmospheric helium abundance is achieved only if a shift in temperature in the existing phase diagrams is applied (-1250 K, +350 K or -3850 K depending on the used phase diagram). We next use the shifted phase diagrams to model Saturn s evolution and find consistent solutions for both planets. We confirm that demixing in Jupiter is modest while in Saturn, the process of helium rain is significant. We find that Saturn has a large helium gradient and a helium ocean. Saturn s atmospheric helium mass fraction is estimated to be between 0.13 and 0.16. We also investigate how the used hydrogen-helium equation of state and atmospheric model affect the planetary evolution and find that the predicted cooling times can change by several hundred million years. Constraining the level of super-adiabaticity in the helium gradient formed in Jupiter and Saturn remains challenging and should be investigated in detail in future research. We conclude that further explorations of the immiscibility between hydrogen and helium are valuable as this knowledge directly affects the evolution and current-state structure of Jupiter and Saturn. Finally, we argue that measuring Saturn s atmospheric helium content is crucial for constraining Saturn s evolution as well as the hydrogen-helium phase diagram.

Accepted for publication in A&A

References in corpus (13)

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• The Possibility of Hydrogen-Water Demixing in Uranus, Neptune, K2-18b and TOI-270d
• Conditions for radiative zones in the molecular hydrogen envelope of Jupiter and Saturn: The role of alkali metals
• Characterizing Jupiter's interior using machine learning reveals four key structures
• The Evolution of Jupiter and Saturn as a function of the Parameter R${}_{\rho }$
• How Internal Structure Shapes the Metallicity of Giant Exoplanets
• Late gas released in the young Kuiper belt could have significantly contributed to the carbon enrichment of the atmospheres of Neptune and Uranus
• Reassessing planetary composition: Evidence of rock-dominated envelopes in Uranus and Neptune
• First-principles simulation of shocked H-He mixture along the principal Hugoniot
• A data-driven estimate of the protosolar helium mass fraction