Microchemical and mineralogical characterization of lunar meteorites aimed at the production and testing of lunar regolith simulants

Introduction: Lunar soil simulants have been produced since 1971, as the upcoming space missions needed astronauts to be trained in conducting scientific field works on the Moon’s surface. [1] However, the first lunar soil simulants were not satisfactory in terms of chemical composition and mineralogy, as they were focused on having the proper engineering properties [2].

Due to the scarcity and limited accessibility of real lunar soils and rocks samples, and as the interest in lunar colonization with In-Situ Resource Utilization (ISRU) is growing, the production of lunar soil simulants has increased over the years [2].

The objective of our work is to develop a new lunar regolith simulant providing a reliable analog in terms of both mineralogy and bulk chemical composition that could be used for experiments on element extraction and for sintering experiments aimed at the production of building materials.

Anorthositic rocks are major constituents of the highland regions of the Moon [3], so we aim at reproducing the composition of a regolith whose major component is anorthositic. 

As lunar meteorites give access to unsampled areas of the Moon’s surface [4], we analyzed microchemically and mineralogically feldspathic lunar breccias and use their chemical composition and modal mineralogy as a reference.

Samples and Methods: We performed microchemical and mineralogical characterization of some lunar feldspathic breccias, specifically of samples of the meteorites NWA 7948 [5], NWA 11273 [6], Bechar 007 [7] and Gadamis 004 [8], four feldspathic lunar breccias with low weathering grade [5-8]. The samples were analyzed through FE-SEM at the University of Camerino and the University of Perugia and FE-EMPA analyses are planned at the University of Firenze. Operation conditions were working distance of 8.5 mm and accelerating voltage of 15 and 20 kV.

We started with synthesizing anorthite plagioclase and fluorapatite. We plan to synthetize glass whose composition resembles that of impact glass, vescicular glass of the agglutinates, and volcanic spherules found on lunar rocks and lunar meteorites. The next step will be to find natural terrestrial pyroxenes and olivines of suitable chemical composition and to add them in adequate amounts.

Results: Petrographic and microchemical investigations on the cited meteorites revealed the dominance of anorthitic plagioclase with average composition An_96.1Ab_3.7Or_0.2 and therefore we focused on the synthesis of anorthite microcrystalline powders with this chemical composition using a muffle furnace in air. Synthesis of fluorapatite is currently ongoing, as is the analysis of terrestrial pyroxenes and olivines.

Acknowledgments: This study was carried out within the Space It Up project funded by the Italian Space Agency, ASI, and the Ministry of University and Research, MUR, under contract n. 2024-5-E.0 - CUP n. I53D24000060005.

References: [1] Slabic A. et al. (2024), NASA Technical Reports Server (NTRS) [2] Taylor L. A., et al. (2016) Planetary and Space Science, 126, 1–7 [3] Jaumann R. et al. (2012) Planetary and Space Science, 74, 15-41 [4] Korotev R. L. (2005) Chemie der Erde, 65, 297-346 [5] Zeng, X. et al. (2018), Meteoritic Planetary Science, 53: 1030-1050. Doi: 10.1111/maps.13049 [6] Huidobro J. et al. (2021), ACS Earth Space Chem, 5: 1333-1342. Doi:10.1021/acsearthspacechem.0c00032. [7] Gattacceca J., et al. (2019), Meteorit Planet Sci, 54: 469-471 doi:10.1111/maps.13215 [8] Gattacceca J. et al. (2023), Meteorit Planet Sci, 58: 901-904 doi:10.1111/maps.13995