Recent seismological studies of the Martian core revealed its relatively low density, suggesting the presence of large amounts of light elements including oxygen and carbon in addition to sulfur. In order to reveal crystallizing solids in the light-element-rich core of Mars, we performed high-pressure melting experiments on Fe-S-O-C alloys at 26–49 GPa using a laser-heated diamond-anvil cell. The liquidus phase relations in the Fe-S-O-C system were determined based on textural and chemical characterizations of recovered samples. The results show that Fe-S-O-C liquids crystallize FeO or FeC in the presence of small amounts of O or C in liquids. Accordingly the liquidus fields of FeS and FeS are small, and the quaternary eutectic point is found to be close to the Fe-FeS binary eutectic point. Under Martian core conditions, S-rich liquids have low liquidus temperatures to crystallize FeO or FeC compared to S-poor liquids. The pressure dependence of liquidus temperatures suggests that crystallization of Mars’ core starts at the center upon cooling. According to the FeO-FeC cotectic surfaces and their liquidus temperatures, an FeO and/or FeC inner core is predicted unless the Martian core remains entirely liquid.

中文翻译：

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火星核心条件下 Fe-S-O-C 合金的熔化实验：火星含 O 和 C 的核心中可能的结构


最近对火星核心的地震学研究揭示了其相对较低的密度，表明除了硫之外还存在大量的轻元素，包括氧和碳。为了揭示富含轻元素的火星核心中的结晶固体，我们使用激光加热金刚石砧池在 26–49 GPa 下对 Fe-S-O-C 合金进行了高压熔化实验。 Fe-S-O-C 体系中的液相线相关系是根据回收样品的结构和化学特征确定的。结果表明，Fe-S-O-C 液体在液体中存在少量 O 或 C 的情况下会结晶出 FeO 或 FeC。因此，FeS和FeS的液相线场较小，并且发现四元共晶点接近于Fe-FeS二元共晶点。在火星核心条件下，与贫硫液体相比，富硫液体的液相线温度较低，无法结晶 FeO 或 FeC。液相线温度的压力依赖性表明，火星核心的结晶在冷却时从中心开始。根据 FeO-FeC 共晶表面及其液相线温度，预测存在 FeO 和/或 FeC 内核，除非火星核心保持完全液态。