Kovačević Tanja, González-Cataldo Felipe, Stewart Sarah T, Militzer Burkhard
Department of Earth and Planetary Science, University of California, Berkeley, CA, 94720, USA.
Department of Earth and Planetary Sciences, University of California, Davis, CA, 95616, USA.
Sci Rep. 2022 Jul 29;12(1):13055. doi: 10.1038/s41598-022-16816-w.
Super-Earths and sub-Neptunes are the most common planet types in our galaxy. A subset of these planets is predicted to be water worlds, bodies that are rich in water and poor in hydrogen gas. The interior structures of water worlds have been assumed to consist of water surrounding a rocky mantle and iron core. In small planets, water and rock form distinct layers with limited incorporation of water into silicate phases, but these materials may interact differently during the growth and evolution of water worlds due to greater interior pressures and temperatures. Here, we use density functional molecular dynamics (DFT-MD) simulations to study the miscibility and interactions of enstatite (MgSiO), a major end-member silicate phase, and water (HO) at extreme conditions in water world interiors. We explore pressures ranging from 30 to 120 GPa and temperatures from 500 to 8000 K. Our results demonstrate that enstatite and water are miscible in all proportions if the temperature exceeds the melting point of MgSiO. Furthermore, we performed smoothed particle hydrodynamics simulations to demonstrate that the conditions necessary for rock-water miscibility are reached during giant impacts between water-rich bodies of 0.7-4.7 Earth masses. Our simulations lead to water worlds that include a mixed layer of rock and water.
超级地球和海王星以下的行星是我们星系中最常见的行星类型。预计这些行星中的一部分是水世界，即富含水且氢气含量低的天体。水世界的内部结构被假定为由围绕岩石地幔和铁核的水组成。在小行星中，水和岩石形成不同的层，水在硅酸盐相中融入有限，但由于内部压力和温度更高，这些物质在水世界的生长和演化过程中可能会有不同的相互作用。在这里，我们使用密度泛函分子动力学（DFT-MD）模拟来研究顽火辉石（MgSiO）（一种主要的端元硅酸盐相）与水（H₂O）在水世界内部极端条件下的混溶性和相互作用。我们探索了30至120吉帕的压力范围和500至8000开尔文的温度范围。我们的结果表明，如果温度超过MgSiO的熔点，顽火辉石和水可以以任意比例互溶。此外，我们进行了光滑粒子流体动力学模拟，以证明在质量为0.7 - 4.7个地球质量的富水天体之间的巨大撞击过程中，会达到岩石与水互溶所需的条件。我们的模拟产生了包含岩石和水混合层的水世界。
