The presence of light elements in the metallic cores of the Earth, the Moon, and other rocky planetary bodies has been widely proposed. Carbon is among the top candidates in light of its high cosmic abundance, siderophile nature, and ubiquity in iron meteorites. It is, however, still controversial whether carbon‐rich core compositional models can account for the seismic velocity observations within the Earth and lunar cores. Here, we report the density and elasticity of Fe₉₀Ni₁₀‐3 wt.% C and Fe₉₀Ni₁₀‐5 wt.% C liquid alloys using synchrotron‐based X‐ray absorption experiments and first‐principles molecular dynamics simulations. Our results show that alloying of 3 wt.% and 5 wt.% C lowers the density of Fe₉₀Ni₁₀ liquid by ∼2.9–3.1% at 2 GPa, and ∼3.4–3.6% at 9 GPa. More intriguingly, our experiments and simulations both demonstrate that the bulk moduli of the Fe‐Ni‐C liquids are similar to or slightly higher than those of Fe‐Ni liquids. Thus, the calculated compressional velocities (v_p) of Fe‐Ni‐C liquids are higher than that of pure Fe‐Ni alloy, promoting carbon as a possible candidate to explain the elevated v_p in the Earth's outer core. However, the values and slopes of both density and v_p of the studied two Fe‐Ni‐C liquids do not match the outer core seismic models, suggesting that carbon may not be the sole principal light element in Earth's outer core. The high v_p of Fe‐Ni‐C liquids does not match the presumptive v_p of the lunar outer core well, indicating that carbon is less likely to be its dominant light element.

中文翻译：

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Fe-Ni-C液体在高压下的密度及其对地球和月球液体核的影响

广泛提出了在地球，月球和其他岩石行星体的金属核中存在轻元素的建议。鉴于其高的宇宙丰度，嗜铁性和在陨铁中的普遍存在，碳是最有可能的候选者之一。但是，富碳岩心组成模型是否可以解释地球和月球岩心内的地震速度观测仍存在争议。这里，我们报告Fe的密度和弹性的₉₀镍₁₀ -3重量％的C和Fe ₉₀镍₁₀ -5重量使用基于同步加速器的X射线吸收实验和第一原理分子动力学模拟％C液态合金。我们的结果表明，将3 wt。％和5 wt。％C合金化会降低Fe ₉₀ Ni的密度₁₀液体在2 GPa时约为2.9-3.1％，在9 GPa时约为3.4-3.6％。更有趣的是，我们的实验和模拟都表明，Fe-Ni-C液体的体积模量与Fe-Ni液体的体积模量相似或略高。因此，计算出的纵波速度（v _p的的Fe-Ni-C液体）是比纯Fe-Ni合金的更高，促进碳作为可能的候选解释升高v _p在地球外核。但是，所研究的两种Fe-Ni-C液体的密度和v _p的值和斜率与外核地震模型不匹配，这表明碳可能不是地球外核的唯一主要轻元素。高v _p的Fe‐Ni‐C液体与月球外核心井的推定v _p不匹配，这表明碳不太可能成为其主要的轻元素。