Light elements are important components that affect the physical and chemical properties and state of the lunar core. Sulfur is probably a dominant candidate. However, the sulfur abundance in the lunar core remains debatable.

Researchers from the Institute of Geochemistry of the Chinese Academy of Sciences (IGCAS) investigated the phase diagram of Fe-S-P ternary system under high-pressure and high-temperature conditions to constrain the abundances of S and P in the lunar core.

They found that S content in solid iron was near negligible and established a relationship of S content in liquid iron. The abundances of S and P were estimated to be 6.08–7.15 wt% and 0.54(1) wt% in the lunar liquid outer core, and 0.05(1) wt% and 0.07(1) wt% in the lunar solid inner core, respectively.

The study was published in Geochimica et Cosmochimica Acta on July 29.

Furthermore, the researchers discussed the formation of the lunar core and demonstrated 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.

This study was supported by the National Natural Science Foundation of China, the Strategic Priority Research Program (B), and the International Partnership Program of the Chinese Academy of Sciences.

Figure 1: Constraints on the (S + P) content (a) in the lunar core and liquidus and adiabatic temperature gradient and freezing regimes (b) of the lunar core (Image by IGCAS)

Figure 2: Evolutionary scenarios of the cooling Fe-S-P lunar core  (Image by IGCAS) 

Contact:
YIN Yuan; ZHAI Shuangmeng
Institute of Geochemistry, the Chinese Academy of Sciences
E-mail: yinyuan@mail.gyig.ac.cn ; zhaishuangmeng@mail.gyig.ac.cn

（By Prof. ZHAI Shuangmeng’s group）