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Impact Resurfacing of the Artemis Exploration Zone: Sample Locations for Primordial Crust and South Pole‐Aitken (SPA) Ejecta.

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Title: Impact Resurfacing of the Artemis Exploration Zone: Sample Locations for Primordial Crust and South Pole‐Aitken (SPA) Ejecta.
Authors: Frueh, T.1,2 (AUTHOR) tfrh@vols.utk.edu, Camon, A.3 (AUTHOR), Boyce, M.4 (AUTHOR), Halwa, S. L.5 (AUTHOR), Ligeza, G.6,7 (AUTHOR), Lemelin, M.3 (AUTHOR), Thomson, B. J.1 (AUTHOR), Kring, D. A.8,9 (AUTHOR)
Source: Journal of Geophysical Research. Planets. Oct2025, Vol. 130 Issue 10, p1-28. 28p.
Subject Terms: Lunar south pole, Moon, Lunar craters, Lunar exploration, Lunar soil, Crust of the earth, Event stratigraphy
Abstract: Regolith samples from the lunar south pole are expected to contain material from the ancient lunar crust and potentially the uppermost mantle, excavated by the South Pole‐Aitken (SPA) impact. In this study, we aim to understand the impact resurfacing processes following the SPA impact and the subsequent redistribution of primordial crust and SPA‐derived mantle material within the initial Artemis exploration zone (AEZ). Our goal is to identify optimal sampling locations for these materials. To achieve this, we reconstruct the south pole stratigraphy by modeling the cumulative thickness of post‐SPA crater materials and estimating the present SPA ejecta thickness. By calculating crater excavation depths, we then infer which craters were excavated from what stratigraphic layer. We estimate a cumulative post‐SPA ejecta layer thickness of ∼190 m to ∼1.8 km across different locations. We infer that all craters >10 km in diameter within the AEZ have likely been excavated below the post‐SPA regolith layer. Based on surficial presence of anorthositic and mafic material, we postulate an SPA ejecta thickness in the AEZ of several hundred meters up to ∼10 km. The extent to which primordial crust and SPA‐derived mantle material have been excavated depends on the wide range of possible SPA ejecta thicknesses. Their surficial presence and sampling potential are influenced by the age of the excavating crater. By integrating the stratigraphic model with mineral maps, we identify promising sampling targets, including regolith with potentially concentrated SPA material in the ejecta blanket of Kocher and primordial crust in the ejecta blanket of Shackleton crater. Plain Language Summary: The lunar south polar region is ancient and densely cratered. It is situated on the rim of the South Pole‐Aitken (SPA) basin, the largest and oldest impact basin on the Moon. The formation of the SPA basin by a massive meteoroid impact may have excavated material from the upper lunar mantle. This material was emplaced as a thick layer of debris on top of the ancient lunar crust. Subsequent cratering events buried the region beneath newer layers of debris. This study investigates how ancient crustal materials and SPA ejecta were redistributed and where to sample these materials. To achieve this, we estimate the thickness of the SPA debris and the combined debris of later impacts. By calculating the depths from which craters excavated material, we determined which impacts likely exposed ancient crust or SPA material. Additionally, we analyzed the surface composition of the south polar region to identify areas with enhanced concentrations of ancient crustal or SPA‐derived material. The results indicate that the ejecta blanket of Kocher crater is the most promising location for sampling SPA materials. In contrast, we identify the ejecta blanket of the Shackleton crater as the best site to access samples of the Moon's primordial crust. Key Points: We reconstruct the lunar south pole stratigraphy, built of the ancient crust, ejecta from the SPA basin, and post‐SPA crater materialsPost‐SPA ejecta layers have a cumulative thickness of ∼190 m to ∼1.8 km and SPA ejecta of ∼100 m to 10 km, depending on the trajectoryConcentrated material from SPA is likely present near Kocher crater and primordial crust near Shackleton crater [ABSTRACT FROM AUTHOR]
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Abstract:Regolith samples from the lunar south pole are expected to contain material from the ancient lunar crust and potentially the uppermost mantle, excavated by the South Pole‐Aitken (SPA) impact. In this study, we aim to understand the impact resurfacing processes following the SPA impact and the subsequent redistribution of primordial crust and SPA‐derived mantle material within the initial Artemis exploration zone (AEZ). Our goal is to identify optimal sampling locations for these materials. To achieve this, we reconstruct the south pole stratigraphy by modeling the cumulative thickness of post‐SPA crater materials and estimating the present SPA ejecta thickness. By calculating crater excavation depths, we then infer which craters were excavated from what stratigraphic layer. We estimate a cumulative post‐SPA ejecta layer thickness of ∼190 m to ∼1.8 km across different locations. We infer that all craters >10 km in diameter within the AEZ have likely been excavated below the post‐SPA regolith layer. Based on surficial presence of anorthositic and mafic material, we postulate an SPA ejecta thickness in the AEZ of several hundred meters up to ∼10 km. The extent to which primordial crust and SPA‐derived mantle material have been excavated depends on the wide range of possible SPA ejecta thicknesses. Their surficial presence and sampling potential are influenced by the age of the excavating crater. By integrating the stratigraphic model with mineral maps, we identify promising sampling targets, including regolith with potentially concentrated SPA material in the ejecta blanket of Kocher and primordial crust in the ejecta blanket of Shackleton crater. Plain Language Summary: The lunar south polar region is ancient and densely cratered. It is situated on the rim of the South Pole‐Aitken (SPA) basin, the largest and oldest impact basin on the Moon. The formation of the SPA basin by a massive meteoroid impact may have excavated material from the upper lunar mantle. This material was emplaced as a thick layer of debris on top of the ancient lunar crust. Subsequent cratering events buried the region beneath newer layers of debris. This study investigates how ancient crustal materials and SPA ejecta were redistributed and where to sample these materials. To achieve this, we estimate the thickness of the SPA debris and the combined debris of later impacts. By calculating the depths from which craters excavated material, we determined which impacts likely exposed ancient crust or SPA material. Additionally, we analyzed the surface composition of the south polar region to identify areas with enhanced concentrations of ancient crustal or SPA‐derived material. The results indicate that the ejecta blanket of Kocher crater is the most promising location for sampling SPA materials. In contrast, we identify the ejecta blanket of the Shackleton crater as the best site to access samples of the Moon's primordial crust. Key Points: We reconstruct the lunar south pole stratigraphy, built of the ancient crust, ejecta from the SPA basin, and post‐SPA crater materialsPost‐SPA ejecta layers have a cumulative thickness of ∼190 m to ∼1.8 km and SPA ejecta of ∼100 m to 10 km, depending on the trajectoryConcentrated material from SPA is likely present near Kocher crater and primordial crust near Shackleton crater [ABSTRACT FROM AUTHOR]
ISSN:21699097
DOI:10.1029/2025JE009050