^1,2Rachel Y. Sheppard, ³Jessica M. Weber, ⁴Laura E. Rodriguez, ³Cathy Trejo, ⁵Elisabeth M. Hausrath, ³Laura M. Barge
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2025.116769]
¹Planetary Science Institute, Tucson, AZ, USA
²Institut d’Astrophysique Spatiale, Université Paris-Saclay, CNRS, Orsay, France
³NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
⁴Lunar and Planetary Institute/USRA, Houston, TX, USA
⁵University of Nevada Las Vegas, Las Vegas, NV, USA
Copyright Elsevier

The high mobility of Li allows it to be used as a tracer for groundwater processes, recording past aqueous conditions. On Earth, a relationship has been noted in multiple field sites between clay mineral abundances and elevated Li in bedrock. Observations from the Curiosity MSL mission at Gale crater on Mars showed a high-clay mineral and high-Li area near the Vera Rubin ridge (VRR) and Glen Torridon region, suggesting Li was perhaps substituting into clay minerals as was seen in these terrestrial field settings. However, the process of this substitution has not been examined in the laboratory using non-field samples, especially not with Mars-relevant mineralogy. To investigate this open question in the laboratory using Mars-relevant regolith and clay minerals, we conducted continuous flow packed-bed reactor experiments to test whether clay minerals affect the Li concentration of Mars regolith simulant MGS-1 during aqueous alteration. The mechanism for Li sorption was also investigated by conducting experiments with clays mixed with glass beads and investigating changes in other elements alongside Li via laser-induced breakdown spectroscopy (LIBS). We tested four dioctahedral clay minerals (kaolinite, illite, nontronite, mixed layer illite/smectite) and two trioctahedral clay minerals (talc, saponite) and found that both talc and illite are capable of increasing the amount of Li sorbed compared to MGS-1 simulant when exposed to Li-bearing groundwater. For MGS-1, the glass beads, and the clay minerals (talc, illite) the primary mechanism appears to be Li substitution for Mg, Al, and K, respectively. This has implications for ongoing Mars missions as well as astrobiology, specifically relating to understanding habitability of areas on Mars and identifying aqueous environments for future mission concepts.

¹Siyu Li, ^1,2Yingnan Zhang, ^1,2Ziwei Wang, ^1,2Bing Yang, ^1,2Liping Qin
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.08.006]
¹Deep Space Exploration Laboratory/State Key Laboratory of Lithospheric and Environmental Coevolution, University of Science and Technology of China, Hefei 230026, China
²CAS Center for Excellence in Comparative Planetology, Hefei 230026, China
Copyright Elsevier

Space weathering alters the chemical and isotopic compositions of the lunar surface, potentially obscuring insights into the formation and evolution of the Moon and terrestrial planets. The contribution of micrometeorite bombardment to the space weathering process, however, is poorly understood. In this study, the Ni isotopic composition of the Chang’e-5 regolith from different depths of a drilling core was studied to examine both the meteoritic addition and evaporation within the local regolith. The Chang’e-5 lunar drill core samples exhibit significantly elevated Ni abundances and higher δ60Ni values (0.54–1.06 ‰) compared to lunar basalt samples (0.18 ± 0.01 ‰), indicating preferential loss of isotopically light Ni due to impact-induced evaporation of high-Ni-content impactors. Notably, the δ60Ni values decrease significantly with depth, while Ni content remains unchanged, suggesting that continuous micrometeorite bombardment, rather than simple mixing of evaporated impactor material, is responsible for the observed Ni isotopic fractionation. Based on the Ni/Co and the Ni isotopic compositions, we estimate that the primary micrometeorite impactors at the Chang’e-5 site are chondritic, contributing ∼1–2 wt% of the regolith, while ∼10–30 % of the Ni from the impactors was evaporated under near-saturated conditions. This process preferentially enriches the upper regolith in heavier Ni isotopes during more extensive micrometeorite bombardment, supporting continuous space weathering processes in relatively young regolith at the Chang’e-5 landing site. These findings not only highlight the long-term effects of micrometeorite-impact-induced degassing during the space weathering on the lunar surface but also provide new insights into regolith gardening and the progressive surface modification of airless planetary bodies.