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Superadiabaticity in Jupiter and Giant Planet Interiors

Debras, Florian and Chabrier, Gilles and Stevenson, David J. (2021) Superadiabaticity in Jupiter and Giant Planet Interiors. Astrophysical Journal Letters, 913 (2). Art. No. L21. ISSN 2041-8205. doi:10.3847/2041-8213/abfdcc.

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Interior models of giant planets traditionally assume that at a given radius (i.e., pressure) the density should be larger than or equal to the one corresponding to a homogeneous, adiabatic stratification throughout the planet (referred to as the "outer adiabat"). The observations of Jupiter's gravity field by Juno combined with the constraints on its atmospheric composition appear to be incompatible with such a profile. In this Letter, we show that the above assumption stems from an incorrect understanding of the Schwarzschild–Ledoux criterion, which is only valid on a local scale. In order to fulfill the buoyancy stability condition, the density gradient with pressure in a nonadiabatic region must indeed rise more steeply than the local adiabatic density gradient. However, the density gradient can be smaller than the one corresponding to the outer adiabat at the same pressure because of the higher temperature in an inhomogeneously stratified medium. Deep enough, the density can therefore be lower than the one corresponding to the outer adiabat. We show that this is permitted only if the slope of the local adiabat becomes shallower than the slope of the outer adiabat at the same pressure, as found in recent Jupiter models due to the increase of both specific entropy and adiabatic index with depth. We examine the dynamical stability of this structure and show that it is stable against nonadiabatic perturbations. The possibility of such an unconventional density profile in Jupiter further complicates our understanding of the internal structure and evolution of (extrasolar) giant planets.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Debras, Florian0000-0002-3113-4840
Chabrier, Gilles0000-0002-8342-9149
Stevenson, David J.0000-0001-9432-7159
Additional Information:© 2021. The American Astronomical Society. Received 2020 October 16; revised 2021 April 22; accepted 2021 May 3; published 2021 May 28. The authors are thankful to Christoph Mordasini, Jérémy Leconte, and Etienne Jaupart for helpful conversations. We are also grateful to the referee whose detailed report greatly helped us in improving the manuscript. This work was supported by the Programme National de Planetologie (PNP) of CNRS-INSU co-funded by CNES. F.D. thanks the European Research Council (ERC) for funding under the H2020 research & innovation program (grant agreement #740651 NewWorlds).
Funding AgencyGrant Number
Programme National de Planetologie (PNP)UNSPECIFIED
Centre National d'Études Spatiales (CNES)UNSPECIFIED
European Research Council (ERC)740651
Subject Keywords:Planetary interior; Exoplanet structure
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Planetary interior (1248); Exoplanet structure (495)
Record Number:CaltechAUTHORS:20210528-094924854
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Official Citation:Florian Debras et al 2021 ApJL 913 L21
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109300
Deposited By: George Porter
Deposited On:28 May 2021 20:24
Last Modified:16 Nov 2021 19:35

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