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The Influence of Space Weathering on the Far‐Ultraviolet Reflectance of Apollo‐Era Soils.

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Title: The Influence of Space Weathering on the Far‐Ultraviolet Reflectance of Apollo‐Era Soils.
Authors: Gimar, C. J.1,2,3 (AUTHOR) caleb.gimar@contractor.swri.org, Raut, U.1,2,3 (AUTHOR), Stevanovic, A.2,4 (AUTHOR), Mayorga, L. C.5 (AUTHOR), Protopapa, S.2,6 (AUTHOR), Byron, B. D.7 (AUTHOR), Retherford, K. D.1,2,3 (AUTHOR), Greathouse, T. K.3 (AUTHOR), Poston, M. J.2,3 (AUTHOR), Cahill, J. T. S.5 (AUTHOR), Qasim, D. N.2,3 (AUTHOR)
Source: Journal of Geophysical Research. Planets. Dec2025, Vol. 130 Issue 12, p1-16. 16p.
Subject Terms: *Ultraviolet radiation, Lunar soil, Backscattering, Spectral sensitivity, Multiple scattering (Physics), Spectrophotometers, Space environment
Company/Entity: Apollo program (U.S.)
Abstract: Building on our previous studies of the far‐ultraviolet (FUV) reflectance of Apollo soil 10084 and lunar soil simulants JSC‐1A and LMS‐1 (Gimar et al., 2022, https://doi.org/10.1029/2022je007508; Raut et al., 2018, https://doi.org/10.1029/2018je005567), we present new FUV results for Apollo soils 68501 and 71061. Heavily weathered soils (68501, 10084)–enriched in submicroscopic Fe, agglutinates, and sub‐micron scale roughness as revealed by our electron microscopy investigations–are darker in the FUV and predominantly backscatter incident light. In contrast, the relatively less weathered subsurface 71061 soil is approximately twice as bright, exhibits forward scattering, and presents a steeper blue spectral slope between 130 and 160 nm compared to the weathered soils. Differences in either primary composition or mineralogy appear to have little to no effect on the FUV albedo or scattering behavior of these soils since the reflectance of high‐Ti mare 10084 and low‐Ti highland 68501 are nearly indistinguishable within error. Further investigation of additional Apollo‐era soils across various maturity indices is needed to fully characterize the influence of space weathering on lunar soil FUV spectrophotometric response. Plain Language Summary: We compare the far‐ultraviolet (FUV, 115–200 nm) reflectance properties of lunar soils 10084, 68501 and 71061 obtained by Apollo missions 11, 16, and 17, respectively. Our measurements show the Apollo 10084 and 68501 soils are very dark and mostly scatter light back toward the source (backscattering) in the FUV. These two soils possess space weathering features such as submicroscopic iron particles in the rims of their grains, agglutinated (melted together) grains, and sub‐micron scale roughness which may contribute to the dark, backscattering nature of these soils. In contrast, 71061 soil–a sub‐surface sample with diminished space weathering features–is nearly twice as bright and mostly scatters FUV light away from the source (forward scattering). Since the FUV reflectance of high‐titanium mare 10084 and low‐titanium highland 68501 are nearly indistinguishable, the space weathering features in the rims of the grains appear to be the dominant influence on the FUV spectral properties of the soils instead of bulk composition. Key Points: We measured the far‐ultraviolet (FUV) bidirectional reflectance of three Apollo‐era lunar soils (10084, 68501, and 71061)Highly space‐weathered lunar soils (10084, 68501) backscatter FUV light; less weathered soil (71061) forward scatters and is more reflectiveSimilar reflectance for high‐Ti (10084) and low‐Ti (68501) soils imply chemical composition does not strongly affect mature soils in the FUV [ABSTRACT FROM AUTHOR]
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Abstract:Building on our previous studies of the far‐ultraviolet (FUV) reflectance of Apollo soil 10084 and lunar soil simulants JSC‐1A and LMS‐1 (Gimar et al., 2022, https://doi.org/10.1029/2022je007508; Raut et al., 2018, https://doi.org/10.1029/2018je005567), we present new FUV results for Apollo soils 68501 and 71061. Heavily weathered soils (68501, 10084)–enriched in submicroscopic Fe, agglutinates, and sub‐micron scale roughness as revealed by our electron microscopy investigations–are darker in the FUV and predominantly backscatter incident light. In contrast, the relatively less weathered subsurface 71061 soil is approximately twice as bright, exhibits forward scattering, and presents a steeper blue spectral slope between 130 and 160 nm compared to the weathered soils. Differences in either primary composition or mineralogy appear to have little to no effect on the FUV albedo or scattering behavior of these soils since the reflectance of high‐Ti mare 10084 and low‐Ti highland 68501 are nearly indistinguishable within error. Further investigation of additional Apollo‐era soils across various maturity indices is needed to fully characterize the influence of space weathering on lunar soil FUV spectrophotometric response. Plain Language Summary: We compare the far‐ultraviolet (FUV, 115–200 nm) reflectance properties of lunar soils 10084, 68501 and 71061 obtained by Apollo missions 11, 16, and 17, respectively. Our measurements show the Apollo 10084 and 68501 soils are very dark and mostly scatter light back toward the source (backscattering) in the FUV. These two soils possess space weathering features such as submicroscopic iron particles in the rims of their grains, agglutinated (melted together) grains, and sub‐micron scale roughness which may contribute to the dark, backscattering nature of these soils. In contrast, 71061 soil–a sub‐surface sample with diminished space weathering features–is nearly twice as bright and mostly scatters FUV light away from the source (forward scattering). Since the FUV reflectance of high‐titanium mare 10084 and low‐titanium highland 68501 are nearly indistinguishable, the space weathering features in the rims of the grains appear to be the dominant influence on the FUV spectral properties of the soils instead of bulk composition. Key Points: We measured the far‐ultraviolet (FUV) bidirectional reflectance of three Apollo‐era lunar soils (10084, 68501, and 71061)Highly space‐weathered lunar soils (10084, 68501) backscatter FUV light; less weathered soil (71061) forward scatters and is more reflectiveSimilar reflectance for high‐Ti (10084) and low‐Ti (68501) soils imply chemical composition does not strongly affect mature soils in the FUV [ABSTRACT FROM AUTHOR]
ISSN:21699097
DOI:10.1029/2025JE009304