Rotation reduces convective mixing in Jupiter and other gas giants

Abstract

Recent measurements of Jupiter's gravitational moments by the Juno spacecraft and seismology of Saturn's rings suggest that the primordial composition gradients in the deep interior of these planets have persisted since their formation. One possible explanation is the presence of a double-diffusive staircase below the planet's outer convection zone, which inhibits mixing across the deeper layers. However, hydrodynamic simulations have shown that these staircases are not long-lasting and can be disrupted by overshooting convection. In this paper we suggests that planetary rotation could be another factor for the longevity of primordial composition gradients. Using rotational mixing-length theory and 3D hydrodynamic simulations, we demonstrate that rotation significantly reduces both the convective velocity and the mixing of primordial composition gradients. In particular, for Jovian conditions at $t\sim 10^8\mathrm{yrs}$ after formation, rotation reduces the convective velocity by a factor of 6, and in turn, the kinetic energy flux available for mixing gets reduced by a factor of $6^3\sim 200$. This leads to an entrainment timescale that is more than two orders of magnitude longer than without rotation. We encourage future hydrodynamic models of Jupiter and other gas giants to include rapid rotation, because the decrease in the mixing efficiency could explain why Jupiter and Saturn are not fully mixed.

Accepted for publication in the Astrophysical Journal Letters

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Cited by in corpus (8)

• Convective Mixing in Gas Giant Planets with Primordial Composition Gradients
• Evolution of Semi-convective Staircases in Rotating Flows: Consequences for Fuzzy Cores in Giant Planets
• Unraveling the origin of giant exoplanets: Observational implications of convective mixing
• The Evolution of Jupiter and Saturn as a function of the Parameter R${}_{\rho }$
• Penetrative magneto-convection of a rotating Boussinesq flow in $f$-planes
• The impact of rotation on the stochastic excitation of stellar acoustic modes in solar-like pulsators
• An Energy Perspective of Core Erosion in Gas Giant Planets
• 3D Simulations of Convective Entrainment in Gas Giants: Rotation and Decreasing Luminosity as Barriers to Mixing