后钙钛矿中铁的不相容性及超级地球中基底岩浆洋的稳定性

中文摘要 AI 辅助

后钙钛矿预计将主导岩石系外行星固体地幔的大部分，然而在这些压力下，后钙钛矿与硅酸盐熔体之间的铁分配——这控制着结晶岩浆洋的成分演化和浮力——尚未得到约束。我们使用第一性原理分子动力学和热力学积分来计算在150-600 GPa和6000-10000 K条件下，后钙钛矿与(Mg,Fe)SiO$_3$液体之间的Fe-Mg分配系数$K_D$。铁在后钙钛矿中强烈不相容，并随压力增加而加剧。将$K_D$与状态方程相结合，我们发现残余液体的铁富集逆转了固-液密度对比，导致后钙钛矿变得浮力。因此，基底岩浆洋在高达4 M$_{\oplus}$的超级地球系外行星中在引力上是稳定的。

英文摘要

Post-perovskite is expected to dominate much of the solid mantles of rocky exoplanets, yet iron partitioning between post-perovskite and silicate melt, which controls the compositional evolution and buoyancy of crystallizing magma oceans, is unconstrained at these pressures. We use first-principles molecular dynamics and thermodynamic integration to compute the Fe--Mg distribution coefficient $K_D$ between post-perovskite and (Mg,Fe)SiO$_3$ liquid at 150--600~GPa and 6000--10000~K. Iron is strongly incompatible in post-perovskite and becomes increasingly so with pressure. Combining $K_D$ with equations of state, we find that iron enrichment of residual liquid reverses the solid--liquid density contrast, causing post-perovskite to become buoyant. Basal magma oceans are therefore gravitationally stable in super-Earth exoplanets up to 4 M$_{\oplus}$.

发表机构

• University of California, Los Angeles（加州大学洛杉矶分校）

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