Far‐UV Observations of Lunar Rayed Craters with LRO‐LAMP

1,2B. D. Byron,1,2K. D. Retherford,2T. K. Greathouse,2D. Wyrick,3J. T. S. Cahill,4A. R. Hendrix,1,2U. Raut,3K. E. Mandt,3B. W. Denevi
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2019JE006269]
1Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX, USA
2Space Science and Engineering Department, Southwest Research Institute, San Antonio, TX, USA
3The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
4Planetary Science Institute, Tucson, AZ, USA
Published by arrangement with John Wiley & Son

Using data from the Lunar Reconnaissance Orbiter (LRO) Lyman Alpha Mapping Project (LAMP), we investigate the spectral properties of rayed craters in the far‐ultraviolet (FUV). Because LAMP is sensitive to the uppermost layer of the lunar surface and regolith grains, it is ideal for characterizing regolith maturity and space weathering products such as submicroscopic iron. We find that crater rays from a survey of the largest Copernican‐age craters have high Off‐band (155–190 nm)/On‐band (130–155 nm) albedo (Off/On) LAMP product ratios, consistent with immature regolith and low amounts of submicroscopic iron. The Off/On ratio of the highlands crater rays decreases linearly over time (0.095 per 100 My), and we use this trend to estimate the age of Jackson crater (~152 My). Some large young highlands craters (e.g., Tycho, Jackson, Giordano Bruno, and Necho) display lower ratio halos around the crater cavity, at regions where previous studies have suggested abundant impact melt exists. The lower Off/On ratio is likely due to the increased glass component of the regolith at these highlands regions, which would act to increase absorption at Off‐band wavelengths. We also find that ejecta blankets from large maria craters (e.g., Copernicus and Aristillus) have a similar Off/On ratio to the mature background highlands. This supports previous findings that determined that the rays from these craters are composed of highlands material excavated from beneath the maria and subsequently weathered to maturity.

 

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