Layered convection as the origin of Saturn's luminosity anomaly

Abstract

As they keep cooling and contracting, Solar System giant planets radiate more energy than they receive from the Sun. Applying the first and second principles of thermodynamics, one can determine their cooling rate, luminosity, and temperature at a given age. Measurements of Saturn's infrared intrinsic luminosity, however, reveal that this planet is significantly brighter than predicted for its age. This excess luminosity is usually attributed to the immiscibility of helium in the hydrogen-rich envelope, leading to "rains" of helium-rich droplets. Existing evolution calculations, however, suggest that the energy released by this sedimentation process may not be sufficient to resolve the puzzle. Here, we demonstrate using planetary evolution models that the presence of layered convection in Saturn's interior, generated, like in some parts of Earth oceans, by the presence of a compositional gradient, significantly reduces its cooling. It can explain the planet's present luminosity for a wide range of configurations without invoking any additional source of energy. This suggests a revision of the conventional homogeneous adiabatic interior paradigm for giant planets, and questions our ability to assess their heavy element content. This reinforces the possibility for layered convection to help explaining the anomalously large observed radii of extrasolar giant planets.

arXiv commentPublished in Nature Geoscience. Online publication date: April 21st, 2013. Accepted version before journal editing and with Supplementary Information

References in corpus (13)

• On the Luminosity of Young Jupiters
• Is tidal heating sufficient to explain bloated exoplanets? Consistent calculations accounting for finite initial eccentricity
• Shock Compression of Deuterium and the Interiors of Jupiter and Saturn
• A new vision on giant planet interiors: the impact of double diffusive convection
• The Heavy Element Masses of Extrasolar Giant Planets, Revealed
• On the Anomalous Radii of the Transiting Extrasolar Planets
• Heat transport in giant (exo)planets: a new perspective
• Phase Separation in Giant Planets: Inhomogeneous Evolution of Saturn
• Rocky core solubility in Jupiter and giant exoplanets
• Self-Consistent Model Atmospheres and the Cooling of the Solar System's Giant Planets
• Phase separation in hydrogen-helium mixtures at Mbar pressures
• A new model for mixing by double-diffusive convection (semi-convection): I. The conditions for layer formation
• Turbulent mixing and layer formation in double-diffusive convection: 3D numerical simulations and theory

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