Evidence for a Dichotomy in the Interior Structures of Jupiter and Saturn from Helium Phase Separation

Abstract

We examine the comparative thermal evolution of Jupiter and Saturn applying recent theoretical results for helium's immiscibility in fluid metallic hydrogen. The redistribution of helium in their interiors proceeds very differently for the two planets. We confirm that based on Jupiter's atmospheric helium depletion as observed in situ by the Galileo entry probe, Jupiter's interior helium has differentiated modestly, and we present models reconciling Jupiter's helium depletion, radius, and heat flow at the solar age. Jupiter's recently revised Bond albedo implies a lower intrinsic flux for the planet, accommodating more luminosity from helium differentiation such that mildly superadiabatic interiors can satisfy all constraints. The same phase diagram applied to the less massive Saturn predicts dramatic helium differentiation to the degree that Saturn inevitably forms a helium-rich shell or core, an outcome previously proposed by Stevenson & Salpeter and others. The luminosity from Saturn's helium differentiation is sufficient to extend its cooling time to the solar age, even for adiabatic interiors. This model predicts Saturn's atmospheric helium to be depleted to Y=0.07+/-0.01, corresponding to a He/H_2 mixing ratio 0.036+/-0.006. We also show that neon differentiation may have contributed to both planets' luminosity in the past. These results demonstrate that Jupiter and Saturn's thermal evolution can be explained self-consistently with a single physical model, and emphasize that nontrivial helium distributions should be considered in future models for Saturn's internal structure and dynamo.

Accepted for publication in ApJ

References in corpus (13)

• Comparing Jupiter interior structure models to Juno gravity measurements and the role of a dilute core
• New models of Jupiter in the context of Juno and Galileo
• Saturn Ring Seismology: Evidence for Stable Stratification in the Deep Interior of Saturn
• Phase separation in hydrogen-helium mixtures at Mbar pressures
• Layered convection as the origin of Saturn's luminosity anomaly
• The Formation of Jupiter's Diluted Core by a Giant Impact
• Jupiter internal structure: the effect of different equations of state
• An Exploration of Double Diffusive Convection in Jupiter as a Result of Hydrogen-Helium Phase Separation
• Convection and Mixing in Giant Planet Evolution
• Models of Saturn's Interior Constructed with Accelerated Concentric Maclaurin Spheroid Method
• Double-diffusive erosion of the core of Jupiter
• The landscape of Saturn's internal magnetic field from the Cassini Grand Finale
• Bayesian Evolution Models for Jupiter with Helium Rain and Double-diffusive Convection

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