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Convective inhibition with an ocean

Markham, S. and Guillot, T. and Stevenson, D. J. (2022) Convective inhibition with an ocean. Astronomy and Astrophysics, 665 . Art. No. A12. ISSN 0004-6361. doi:10.1051/0004-6361/202243359.

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Aims. In this work we generalize the notion of convective inhibition to apply it to cases where there is an infinite reservoir of condensible species (i.e., an ocean). We propose a new model for the internal structure and thermal evolution of super-Earths with hydrogen envelopes. Methods. We derive the criterion for convective inhibition in a generalized phase mixture from first principles thermodynamics. We then investigate the global ocean case using a water-hydrogen system, for which we have data, as an example. After illustrating the relevant thermodynamics, we extend our arguments to apply to a system of hydrogen and silicate vapor. We then employ a simple atmospheric model to apply our findings to super-Earths and to make predictions about their internal structures and thermal evolution. Results. For hydrogen envelope masses roughly in the range 10⁻³−10⁻¹ M_⊕, convective contact between the envelope and core may shut down because of the compositional gradient that arises from silicate partial vaporization. For envelope hydrogen masses that cause the associated basal pressure to exceed the critical pressure of pure silicate (on the order of a couple kilobars), the base of that envelope and the top of the core lie on the critical line of the two-phase hydrogen-silicate phase diagram. The corresponding temperature is much higher than convective models would suggest. The core is then “supercritical” in the sense that the temperature exceeds the critical temperature for pure silicate. The core then cools inefficiently, with intrinsic heat fluxes potentially comparable to the Earth’s internal heat flux today. Conclusions. This low heat flux may allow the core to remain in a high entropy supercritical state for billions of years, but the details of this depend on the nature of the two-component phase diagram at high pressure, something that is currently unknown. A supercritical core thermodynamically permits the dissolution of large quantities of hydrogen into the core.

Item Type:Article
Related URLs:
URLURL TypeDescription
Guillot, T.0000-0002-7188-8428
Stevenson, D. J.0000-0001-9432-7159
Additional Information:This work has been primarily funded by NASA FINESST grant number 80NSSC19K1520, as well as funding from the CNES postdoctoral program. We would also like to thank Yayaati Chachan for many insightful conversations, and the reviewer for highly constructive feedback.
Funding AgencyGrant Number
NASA Earth and Space Science Fellowship80NSSC19K1520
Centre National d'Études Spatiales (CNES)UNSPECIFIED
Record Number:CaltechAUTHORS:20220916-666087000
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:117031
Deposited By: Olivia Warschaw
Deposited On:25 Oct 2022 21:01
Last Modified:25 Oct 2022 21:02

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