^1,2Yanze Su,^1,2Luyuan Xu,^1,2Meng-Hua Zhu
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2024JE008501]
¹State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, China
²CNSA Macau Center for Space Exploration and Science, Macau, China
Published by arrangement with John Wiley & Sons

The composition of lunar samples sheds light on the Moon’s evolutional history. Analyses of Chang’e-5 (CE-5) lunar soils showed <5% of foreign materials, significantly less than numerical predictions (∼10%). To address this inconsistency, we simulated the impact gardening process, accounting for distal ejecta, and tracked the compositional changes in the top 1 m layer at CE-5 landing area over time. Our results show that impact gardening brings deeper local materials to the surface, leading to a mixture that reduces the distal ejecta proportion within the top 1 m layer from which the soils were collected. After 2.0 Gyr of impact gardening, most materials of the top 1 m layer originate from the upper layer (depth <30 m) of local basalts, with distal ejecta as a minor component (∼2.7 vol.%), consistent with CE-5 soils analyses. Our results emphasize the profound influence of impact gardening on the composition of lunar soils.

¹Parsons Levben, ¹Black Benjamin, ²Karunatillake Suniti
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2025.116491]
¹Department of Earth and Planetary Sciences, Rutgers University, 610 Taylor Rd., Piscataway, NJ 08854, United States of America
²Department of Geology and Geophysics, Louisiana State University, E235 Howe Russell Kniffen, Baton Rouge, LA 70803, United States of America
Copyright Elsevier

The sulfur cycle on Mars plays a critical role in shaping its surface and atmospheric chemistry. Mars’ near-surface sulfur inventory largely originated from mantle-derived magmas that erupted during the Noachian, Hesperian, and Amazonian eons. Satellites permit measurements of bulk sulfur in Martian regolith, and rover and meteorite measurements capture snapshots of sulfur in specific samples. However, the concentration of sulfur in Martian magmas prior to degassing, which governs the transfer of interior sulfur to the near-surface, remains uncertain. Because Mars’ mantle may be sulfur-rich, most primary mantle melts are expected to be in equilibrium with residual mantle sulfide. In this work, we therefore use Gamma Ray Spectroscopy (GRS) regional maps of bulk surface chemistry to calculate the sulfur concentration at sulfide saturation (SCSS) for late Noachian through Amazonian Martian magmas. We further consider a range in mantle source sulfur and constraints on degree of melting to account for mantle sulfide exhaustion, in order to estimate sulfur concentrations in primitive melts. We find that the concentration of sulfur in Martian magmas ranged between ~1330 and 4550 ppm S. These results underscore that the GRS sulfur concentration data, from ~15,000 and 29,000 ppm globally, do not represent the sulfur content of primitive basalts, but rather reflect myriad processes that cycled sulfur within the critical zone of exchange between the atmosphere and crust. We define a new metric, the Sulfur Enrichment Index (SEI), that tracks the enrichment in present-day regolith sulfur relative to the original magmatic sulfur concentration in volcanic regions. We show that sulfur release is inefficient for magmas emplaced at >1–2 km depth. Accounting for the total extruded volume of magma from the late Noachian through the Amazonian, our estimates of primary magmatic sulfur concentrations lead to a cumulative yield of ~2–68 × 1019 g of sulfur to the Martian atmosphere from ~3.8 Ga to the present. For comparison, only ~1018–1019 g of sulfur is evident within the upper decimeters of the Martian crust at mid-latitudes. We therefore infer that volcanogenic sulfur, like water, has likely been sequestered within Mars’ crust.