The Abdus Salam International Centre for Theoretical Physics, Trieste I-34151, Italy.
Nat Commun. 2011 Feb 8;2:185. doi: 10.1038/ncomms1184.
The interiors of Neptune and Uranus are believed to be primarily composed of a fluid mixture of methane and water. The mixture is subjected to pressures up to several hundred gigapascal, causing the ionization of water. Laboratory and simulation studies so far have focused on the properties of the individual components. Here we show, using first-principle molecular dynamic simulations, that the properties of the mixed fluid are qualitatively different with respect to those of its components at the same conditions. We observe a pressure-induced softening of the methane-water intermolecular repulsion that points to an enhancement of mixing under extreme conditions. Ionized water causes the progressive ionization of methane and the mixture becomes electronically conductive at milder conditions than pure water, indicating that the planetary magnetic field of Uranus and Neptune may originate at shallower depths than currently assumed.
海王星和天王星的内部被认为主要由甲烷和水的流体混合物组成。该混合物承受高达数百 GPa 的压力，导致水的电离。迄今为止，实验室和模拟研究主要集中在各个成分的性质上。在这里，我们使用第一性原理分子动力学模拟表明，混合流体的性质在相同条件下与各成分的性质明显不同。我们观察到甲烷-水分子间斥力在压力下的软化，表明在极端条件下混合增强。电离水导致甲烷的逐步电离，并且混合物在比纯水更温和的条件下变得具有导电性，这表明天王星和海王星的行星磁场可能起源于比目前假设的更浅的深度。
