Double superionicity in icy compounds at planetary interior conditions

The elements hydrogen, carbon, nitrogen and oxygen are assumed to comprise the bulk of the interiors of the ice giant planets Uranus, Neptune, and sub-Neptune exoplanets. The details of their interior structures have remained largely unknown because it is not understood how the compounds H 2 O, NH 3...

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Bibliographic Details
Published in:Nature communications 2023-11, Vol.14 (1), p.7580-7580, Article 7580
Main Authors: de Villa, Kyla, González-Cataldo, Felipe, Militzer, Burkhard
Format: Article
Language:English
Subjects:
639/33/445/846
704/445/846
Ammonia
Carbon
Conductivity
Extrasolar planets
Heavy nuclei
High pressure
High temperature
Humanities and Social Sciences
Hydrogen
Hydrogen ions
Mathematical models
multidisciplinary
Neptune
Nitrogen
Phase transitions
Planetary interiors
Science
Science (multidisciplinary)
Simulation
Temperature
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Summary:The elements hydrogen, carbon, nitrogen and oxygen are assumed to comprise the bulk of the interiors of the ice giant planets Uranus, Neptune, and sub-Neptune exoplanets. The details of their interior structures have remained largely unknown because it is not understood how the compounds H 2 O, NH 3 and CH 4 behave and react once they have been accreted and exposed to high pressures and temperatures. Here we study thirteen H-C-N-O compounds with ab initio computer simulations and demonstrate that they assume a superionic state at elevated temperatures, in which the hydrogen ions diffuse through a stable sublattice that is provided by the larger nuclei. At yet higher temperatures, four of the thirteen compounds undergo a second transition to a novel doubly superionic state, in which the smallest of the heavy nuclei diffuse simultaneously with hydrogen ions through the remaining sublattice. Since this transition and the melting transition at yet higher temperatures are both of first order, this may introduce additional layers in the mantle of ice giant planets and alter their convective patterns. At high pressures, water and ammonia are known to exhibit superionic states. Here it is shown that many planetary ices (H-C-N-O compounds) exhibit a superionic state, and in some cases, a doubly superionic state, in which multiple elements diffuse simultaneously.
ISSN:2041-1723
2041-1723
DOI:10.1038/s41467-023-42958-0