アポロ17号のサンプルで月の硫黄同位体を新たに発見（Sulfur isotopes in Apollo samples reveal exotic Moon chemistry）

2025-10-06 ブラウン大学

Dottin and co-author Brian Monteleone analyze data from the secondary ion mass spectrometry analysis of Apollo 17 samples.

＜関連情報＞

• https://www.brown.edu/news/2025-10-06/sulfur-isotopes-apollo-samples
• https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024JE008834

月のマントルに存在する内因性かつ異質な硫黄 Endogenous, yet Exotic, Sulfur in the Lunar Mantle

J. W. Dottin III, S. B. Simon, C. K. Shearer, J. Benson, H. Fu, J. S. Boesenberg, B. Monteleone, the ANGSA Science Team
Journal of Geophysical Research:Planets  Published: 10 September 2025
DOI:https://doi.org/10.1029/2024JE008834

Abstract

In situ sulfur isotope analyses of sulfides found in regolith particles from the recently opened Apollo 17 drive tube 73001/2 reveal variable ³⁴S/³²S and ³³S/³²S that range from that of typical lunar basalts to strongly ³⁴S- and ³³S-depleted values (δ³⁴S = −4.1 ± 0.35 to +1.5 ± 0.029; Δ³³S = −2.8 ± 0.48 to −0.1 ± 0.27 (2σ)). All Δ³³S and δ³⁴S data are positively correlated. The correlation indicates mixing between at least two distinct sources of sulfur in the lunar mantle, one of which is associated with photochemically processed sulfur from a gaseous environment (strongly negative Δ³³S). The gaseous precursor and its preservation in endogenous sulfides require that either the sulfur was delivered to the lunar mantle early in its history through unknown processes or it is a remnant of the giant Moon-forming impactor.

Plain Language Summary

The leading hypotheses for the origin of the Moon call for a giant impact event between proto-Earth and a separate impactor (Theia). The efficiency of mixing material among these two planetary bodies remains a subject of debate. Inefficient mixing during this process could leave behind remnants of the composition of the proto-Earth and/or Theia. The sulfur isotope composition of primordial components that survived this impact event could be used to place constraints on early solar nebula chemistry and the distribution of S components throughout the early solar system, as well as the efficiency of mixing during the giant Moon-forming impact event. This study presents anomalous sulfur isotope data from lunar rocks that indicate the presence of either (a) exotic chemistry and crustal recycling during the early evolution of the Moon or (b) material that was not well mixed during the giant Moon-Forming impact event.

Key Points

• Sulfides in regolith particles from the recently opened Apollo 17 drive tube were analyzed for sulfur isotopic and elemental compositions
• Sulfur isotope measurements reveal evidence of multiple lunar mantle sulfur sources
• One mantle source has an unusual sulfur-33 composition that requires delivery during early lunar evolution and inefficient mantle mixing