A new vision of giant planet interiors: Impact of double diffusive convection

¹ École normale supérieure de Lyon, CRAL (CNRS), 46 allée d’Italie, 69007 Lyon, Université de Lyon, France
e-mail: jeremy.leconte@ens-lyon.fr; chabrier@ens-lyon.fr
² School of Physics, University of Exeter, Exeter, UK

Received: 29 July 2011
Accepted: 21 January 2012

Abstract

While conventional interior models for Jupiter and Saturn are based on the simplistic assumption of a solid core surrounded by a homogeneous gaseous envelope, we have derived new models with an inhomogeneous distribution of heavy elements within these planets. Such a compositional gradient hampers large-scale convection that turns into double-diffusive convection, yielding an inner thermal profile that departs from the traditionally assumed adiabatic interior and affecting these planets heat content and cooling history. To address this problem, we have developed an analytical approach to describe layered double-diffusive convection and apply this formalism to solar system gaseous giant planet interiors. These models satisfy all observational constraints and yield values for the metal enrichment of our gaseous giants that are up to 30% to 60% higher than previously thought. The models also constrain the size of the convective layers within the planets. Because the heavy elements tend to be redistributed within the gaseous envelope, the models predict smaller than usual central cores inside Saturn and Jupiter, with possibly no core for the latter. These models open a new window and raise new challenges to our understanding of the internal structure of giant (solar and extrasolar) planets, in particular on how to determine their heavy material content, a key diagnostic for planet formation theories.