Rayleigh–Taylor (RT) instability, which occurs when a heavy fluid overlies a light fluid in a gravitational field, is an important scenario for planetary core formation, especially beneath the planetary magma ocean. This process has been discussed based on numerical simulations and experiments using analog materials. However, experiments on the RT instability using the core-forming melt have not been performed at high pressures. In this study, we perform in situ observation of the RT instability of liquid Fe and Fe–Si (Si = 10 and 20 wt. %) alloys under high pressure using a high-power laser-shock technique. The observed perturbation on the Fe–Si surface grows exponentially with time, while there is no obvious growth of perturbations on the Fe in the measured time range. Therefore, the growth rate of the RT instability increases with Si content. The timescale of the initial growth of the RT instability in planetary interiors is likely to be much faster (by more than two orders of magnitude) than the 30–40 × 10⁶ year timescale of planetary core formation.

中文翻译：

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极端条件下液态铁和铁硅合金瑞利-泰勒不稳定性的原位观察：对行星核心形成的影响

Rayleigh-Taylor (RT) 不稳定性，当重流体覆盖在引力场中的轻流体时会发生，是行星核心形成的重要场景，尤其是在行星岩浆海洋之下。这个过程已经基于数值模拟和使用模拟材料的实验进行了讨论。然而，尚未在高压下进行使用成核熔体的 RT 不稳定性实验。在这项研究中，我们在原位执行使用高功率激光冲击技术在高压下观察液态 Fe 和 Fe-Si（Si = 10 和 20 重量％）合金的 RT 不稳定性。观察到的 Fe-Si 表面的扰动随时间呈指数增长，而在测量的时间范围内，Fe 上的扰动没有明显的增长。因此，RT 不稳定性的增长速度随着 Si 含量的增加而增加。行星内部 RT 不稳定性的初始增长的时间尺度可能比行星核心形成的 30-40 × 10 ⁶年时间尺度快得多（超过两个数量级）。