de Villa Kyla, González-Cataldo Felipe, Militzer Burkhard
Department of Earth and Planetary Science, University of California, Berkeley, CA, 94720, USA.
Department of Astronomy, University of California, Berkeley, CA, 94720, USA.
Nat Commun. 2023 Nov 21;14(1):7580. doi: 10.1038/s41467-023-42958-0.
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 HO, NH and CH 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.
氢、碳、氮和氧元素被认为构成了冰巨行星天王星、海王星以及海王星以下系外行星内部的大部分物质。它们内部结构的细节在很大程度上仍然未知，因为人们并不了解化合物HO、NH和CH一旦被吸积并暴露于高压和高温下会如何表现和反应。在这里，我们用从头算计算机模拟研究了13种H-C-N-O化合物，并证明它们在高温下会呈现超离子态，其中氢离子通过由较大原子核提供的稳定亚晶格扩散。在更高的温度下，这13种化合物中的四种会经历第二次转变，进入一种新型的双超离子态，其中最小的重原子核与氢离子同时通过剩余的亚晶格扩散。由于这种转变以及在更高温度下的熔化转变都是一级的，这可能会在冰巨行星的地幔中引入额外的层次，并改变它们的对流模式。
