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Analysis of Space Weathering Trends of Lunar Swirls in Highlands and Mare

Presentation #101.03 in the session Moon & Earth I (Oral Presentation)

Published onOct 23, 2023
Analysis of Space Weathering Trends of Lunar Swirls in Highlands and Mare

Lunar swirls are photometric anomalies that are associated with magnetic anomalies, though not all lunar magnetic anomalies possess swirls. New models and maps of lunar magnetism lend insight into near-surface processes that may affect space weathering, such as solar wind standoff. Solar wind standoff is one proposed theory of swirl formation that has been indirectly observed, replicated experimentally, and modeled using different techniques. Under typical space weathering conditions, solar wind particles and micrometeoroids incident upon the lunar surface cause regolith maturation that manifests as brightening at the Lyman-alpha wavelength (~121.6 nm) and blueing of far-ultraviolet (FUV) spectral slopes (150–200 nm). The solar wind standoff theory suggests that the deflection of solar wind particles by some magnetic anomalies disrupts part of the space weathering process, forming photometric anomalies that appear optically immature compared to the surrounding regolith. The relationship between lunar swirls and their associated magnetic anomalies is complex, as near-surface field geometry, intensity, and relative solar wind exposure may influence the development of a photometric anomaly. The sensitivity of UV wavelengths to space weathering byproducts has been leveraged to analyze properties of swirls and the relationship of magnetic field geometry and intensity to UV reflectance [Hendrix et al., 2012; Hendrix et al., 2016; Waller et al., 2022]. Recent work indicates that space weathering trends may subtly differ for swirls found in the highlands versus swirls found in mare [Blewett et al., 2021a]. To further investigate this dichotomy and explore the sensitivity of UV wavelengths to submicroscopic iron (SMFe) particle abundances, five swirls and their associated magnetic anomalies were modeled and profiled using the methods of Waller et al. [2022]. In all five cases, the swirls were found to have sufficient magnetic geometry and intensity to potentially form miniature magnetospheres above the surface, even under typical compression from incident solar wind dynamic pressure. Initial results support the influence of regional composition on swirl expression, even when considering latitudinal trends in space weathering. UV wavelength observations compared to modeled SMFe particle abundances suggest that nanosize iron particle abundances may have the most profound effect on FUV reflectance of the swirls. Results from ongoing laboratory work to quantify UV wavelength sensitivity to maturity are used to interpret the profiles sampled across each swirl.

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