High-pressure and high-temperature experiments for the FeSP ternary system were performed at 3–5 GPa and 1173–1873 K. We systematically investigated the effect of pressure, temperature, and bulk composition on the phase relationships, on the core crystallization sequences, and on the presence of sulfur and phosphorous in the lunar core. Our experimental results indicate that while up to < 1 wt% phosphorus can be dissolved in solid iron in the FeSP ternary system at 3 and 5 GPa, S dissolution in solid iron is near negligible. On the iron rich (S + P < 10 wt%) side of the FeSP phase diagram completely miscible FeSP liquids were observed. Combined with previous experimental results, the relationship of the sulfur content in the liquid metal ($X_S^{\mathit{liquid}}$) and the partitioning coefficient of phosphorus (D_P) between the solid and liquid metal follows an equation of $\mathit{lg}{D}_P=-1.8286-17.87\times \mathit{lg}\left(1-X_S^{\mathit{liquid}}\right).$ Tradeoff between the liquidus of the FeSP system and the (S + P) content of the lunar core well constrain the upper limit of the (S + P) content in the liquid lunar outer core to the concentrations between 8.7 and 13.1 wt%. Using the result of the phosphorus coefficient and our partitioning model, we further assessed the abundances of 6.08–7.15 wt% S, 0.54 ± 0.01 wt% P in the lunar liquid outer core, and 0.05 ± 0.01 wt% S, 0.07 ± 0.01 wt% P in the lunar solid inner core, respectively. Integrating the observed lunar core adiabat and the pressure dependence of the FeSP liquidus temperature, we propose that the solidification regime in the lunar core will switch from bottom-up to top-down once the abundance of (S + P) in the liquid outer core exceeds 3.5 wt% as the core evolves.

Fe SP 三元体系的高压和高温实验是在 3-5 GPa 和1173-1873 K 下进行的。我们系统地研究了压力、温度和体积组成对相关系、核心结晶的影响序列，以及月球核心中硫和磷的存在。我们的实验结果表明，在 3 GPa 和 5 GPa 的 Fe SP 三元体系中，虽然高达 < 1 wt% 的磷可以溶解在固体铁中，但S在固体铁中的溶解几乎可以忽略不计。在 Fe S P 相图的富铁 (S + P < 10 wt%) 侧完全混溶 Fe S观察到P液体。结合以往的实验结果，液态金属中硫含量的关系（$X_{\mathrm{小号}}^{\mathit{液体}}$) 和固体和液体金属之间的磷分配系数 ( D _{P ) 遵循以下方程}$\mathit{lg}{D}_{磷}=-1.8286-17.87\times \mathit{lg}\left(1-X_{\mathrm{小号}}^{\mathit{液体}}\right).$Fe S P 系统液相线和月核的（S + P）含量之间的权衡将液态月球外核中（S + P）含量的上限限制在8.7和13.1 wt％之间的浓度. 利用磷系数的结果和我们的分配模型，我们进一步评估了月球液体外核中 6.08-7.15 wt% S、0.54 ± 0.01 wt% P 和 0.05 ± 0.01 wt% S、0.07 ± 0.01 wt% 的丰度% P 在月球固体内核中，分别。综合观察到的月核绝热条件和 Fe S P 液相线温度的压力依赖性，我们提出一旦液体中 (S + P) 的丰度，月核中的凝固状态将从自下而上转变为自上而下随着地核的演化，外核超过 3.5 wt%。