Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011ess.....2.3701l&link_type=abstract
American Astronomical Society, ESS meeting #2, #37.01
Astronomy and Astrophysics
Astronomy
Scientific paper
While conventional interior models for giant (exo)planets are based on the simplistic assumption of a solid core surrounded by a homogeneous gaseous envelope, we derive new models with an inhomogeneous distribution of heavy elements, i.e. a gradient of composition within these planets. Because such a continuous heavy element gradient impedes large-scale convection, the inner thermal profile of these «semi-convective» planets departs from the traditionally assumed adiabatic one. This yields a slower cooling, thus contraction, than in the fully convective, adiabatic case, possibly providing the missing piece to the puzzle of anomalously inflated Hot Jupiters.
In order to test the viability of this hypothesis, we derive semi-convective, inhomogeneous structure models for Jupiter and Saturn which satisfy all observational constraints (gravitational moments, surface abundances), while being substantially super adiabatic. The larger internal temperature in the semi-convective planet, which implies a larger fraction of heavy elements to counteract the radius increase, leads to metal enrichments up to 30 to 60% larger than previously thought for our gas giants. However, as 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 this latter.
As these new structural and cooling properties directly apply to extrasolar planets, we also examine the efficiency of this «bloating mechanism» by quantifying the impact of the reduced heat flux due to semi-convection on the contraction/cooling of Hot Jupiters. Such a possibility of semi-convective planetary interiors opens a new window on our understanding of giant planet formation, structure and evolution, inside and outside our Solar System.
Chabrier Gilles
Leconte Jérémy
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