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Title: Planetary Ices and the Linear Mixing Approximation

Abstract

Here, the validity of the widely used linear mixing approximation (LMA) for the equations of state (EOSs) of planetary ices is investigated at pressure–temperature conditions typical for the interiors of Uranus and Neptune. The basis of this study is ab initio data ranging up to 1000 GPa and 20,000 K, calculated via density functional theory molecular dynamics simulations. In particular, we determine a new EOS for methane and EOS data for the 1:1 binary mixtures of methane, ammonia, and water, as well as their 2:1:4 ternary mixture. Additionally, the self-diffusion coefficients in the ternary mixture are calculated along three different Uranus interior profiles and compared to the values of the pure compounds. We find that deviations of the LMA from the results of the real mixture are generally small; for the thermal EOSs they amount to 4% or less. The diffusion coefficients in the mixture agree with those of the pure compounds within 20% or better. Finally, a new adiabatic model of Uranus with an inner layer of almost pure ices is developed. The model is consistent with the gravity field data and results in a rather cold interior ($${T}_{\mathrm{core}}\sim 4000$$ K).

Authors:
ORCiD logo [1]; ORCiD logo [2];  [3]; ORCiD logo [4];  [5];  [5]; ORCiD logo [2]; ORCiD logo [2];  [2]; ORCiD logo [6];  [5]
  1. Univ. Rostock, Rostock (Germany); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  4. Univ. Rostock, Rostock (Germany); Univ. of California, Santa Cruz, CA (United States)
  5. Univ. Rostock, Rostock (Germany)
  6. Univ. of California, Santa Cruz, CA (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1415412
Report Number(s):
LA-UR-17-25748
Journal ID: ISSN 1538-4357; TRN: US1800809
Grant/Contract Number:  
AC52-06NA25396
Resource Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 848; Journal Issue: 1; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; diffusion; equation of state; planets and satellites: composition; planets and satellites: individual (Uranus, Neptune); planets and satellites: interiors

Citation Formats

Bethkenhagen, M., Meyer, Edmund Richard, Hamel, S., Nettelmann, N., French, M., Scheibe, L., Ticknor, Christopher, Collins, Lee A., Kress, Joel David, Fortney, J. J., and Redmer, R. Planetary Ices and the Linear Mixing Approximation. United States: N. p., 2017. Web. doi:10.3847/1538-4357/aa8b14.
Bethkenhagen, M., Meyer, Edmund Richard, Hamel, S., Nettelmann, N., French, M., Scheibe, L., Ticknor, Christopher, Collins, Lee A., Kress, Joel David, Fortney, J. J., & Redmer, R. Planetary Ices and the Linear Mixing Approximation. United States. doi:10.3847/1538-4357/aa8b14.
Bethkenhagen, M., Meyer, Edmund Richard, Hamel, S., Nettelmann, N., French, M., Scheibe, L., Ticknor, Christopher, Collins, Lee A., Kress, Joel David, Fortney, J. J., and Redmer, R. Tue . "Planetary Ices and the Linear Mixing Approximation". United States. doi:10.3847/1538-4357/aa8b14. https://www.osti.gov/servlets/purl/1415412.
@article{osti_1415412,
title = {Planetary Ices and the Linear Mixing Approximation},
author = {Bethkenhagen, M. and Meyer, Edmund Richard and Hamel, S. and Nettelmann, N. and French, M. and Scheibe, L. and Ticknor, Christopher and Collins, Lee A. and Kress, Joel David and Fortney, J. J. and Redmer, R.},
abstractNote = {Here, the validity of the widely used linear mixing approximation (LMA) for the equations of state (EOSs) of planetary ices is investigated at pressure–temperature conditions typical for the interiors of Uranus and Neptune. The basis of this study is ab initio data ranging up to 1000 GPa and 20,000 K, calculated via density functional theory molecular dynamics simulations. In particular, we determine a new EOS for methane and EOS data for the 1:1 binary mixtures of methane, ammonia, and water, as well as their 2:1:4 ternary mixture. Additionally, the self-diffusion coefficients in the ternary mixture are calculated along three different Uranus interior profiles and compared to the values of the pure compounds. We find that deviations of the LMA from the results of the real mixture are generally small; for the thermal EOSs they amount to 4% or less. The diffusion coefficients in the mixture agree with those of the pure compounds within 20% or better. Finally, a new adiabatic model of Uranus with an inner layer of almost pure ices is developed. The model is consistent with the gravity field data and results in a rather cold interior (${T}_{\mathrm{core}}\sim 4000$ K).},
doi = {10.3847/1538-4357/aa8b14},
journal = {The Astrophysical Journal (Online)},
number = 1,
volume = 848,
place = {United States},
year = {2017},
month = {10}
}

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    Works referencing / citing this record:

    Evidence for Crystalline Structure in Dynamically-Compressed Polyethylene up to 200 GPa
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