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Evidence for a Dichotomy in the Interior Structures of Jupiter and Saturn from Helium Phase Separation

Mankovich, Christopher R. and Fortney, Jonathan J. (2020) Evidence for a Dichotomy in the Interior Structures of Jupiter and Saturn from Helium Phase Separation. Astrophysical Journal, 889 (1). Art. No. 51. ISSN 1538-4357. https://resolver.caltech.edu/CaltechAUTHORS:20200124-135931748

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Abstract

We examine the comparative thermal evolution of Jupiter and Saturn, applying recent theoretical results for helium's immiscibility in fluid metallic hydrogen. The redistribution of helium in their interiors proceeds very differently for the two planets. We confirm that, based on Jupiter's atmospheric helium depletion as observed in situ by the Galileo entry probe, Jupiter's interior helium has differentiated modestly, and we present models reconciling Jupiter's helium depletion, radius, and heat flow at the solar age. Jupiter's recently revised Bond albedo implies a higher intrinsic flux for the planet, accommodating more luminosity from helium differentiation, such that mildly superadiabatic interiors can satisfy all constraints. The same phase diagram applied to the less massive Saturn predicts dramatic helium differentiation, to the degree that Saturn inevitably forms a helium-rich shell or core, an outcome previously proposed by Stevenson & Salpeter and others. The luminosity from Saturn's helium differentiation is sufficient to extend its cooling time to the solar age, even for adiabatic interiors. This model predicts Saturn's atmospheric helium to be depleted to Y = 0.07 ± 0.01, corresponding to a He/H₂ mixing ratio 0.036 ± 0.006. We also show that neon differentiation may have contributed to both planets' luminosity in the past. These results demonstrate that Jupiter and Saturn's thermal evolution can be explained self-consistently with a single physical model, and emphasize that nontrivial helium distributions should be considered in future models for Saturn's internal structure and dynamo.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-4357/ab6210DOIArticle
https://arxiv.org/abs/1912.01009arXivDiscussion Paper
ORCID:
AuthorORCID
Mankovich, Christopher R.0000-0002-4940-9929
Fortney, Jonathan J.0000-0002-9843-4354
Additional Information:© 2020 The American Astronomical Society. Received 2019 September 17; revised 2019 December 12; accepted 2019 December 14; published 2020 January 24. The authors give thanks to the anonymous referee for helpful critiques, and to M. Schöttler for providing the phase diagram data used for this work. This work was supported by NASA through Earth and Space Science Fellowship program grant NNX15AQ62H to C.M., as well as Cassini Participating Scientist program grant NNX16AI43G to J.J.F. Facility: ADS. - Software: emcee (Foreman-Mackey et al. 2013), SciPy (Jones et al. 2001), NumPy (Oliphant 2006), Matplotlib (Hunter 2007).
Funders:
Funding AgencyGrant Number
NASA Earth and Space Science FellowshipNNX15AQ62H
NASANNX16AI43G
Subject Keywords:Jupiter; Saturn; Planetary interior; Planetary structure
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Jupiter (873); Saturn (1426); Planetary interior (1248); Planetary structure (1256)
Record Number:CaltechAUTHORS:20200124-135931748
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200124-135931748
Official Citation:Christopher R. Mankovich and Jonathan J. Fortney 2020 ApJ 889 51
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100905
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:25 Jan 2020 03:31
Last Modified:25 Jan 2020 03:31

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