The Planetary Science Journal (Jan 2023)

New Insights into Aristarchus Crater with LRO LAMP Far-ultraviolet Observations

  • Elizabeth Czajka,
  • Kurt Retherford,
  • Georgiana Kramer,
  • Amanda Hendrix,
  • Joshua Cahill,
  • Benjamin Byron,
  • Benjamin Greenhagen,
  • Thomas Greathouse,
  • Lizeth Magaña,
  • Kathleen Mandt,
  • Cesare Grava

DOI
https://doi.org/10.3847/PSJ/acdee9
Journal volume & issue
Vol. 4, no. 8
p. 137

Abstract

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Aristarchus crater is a Copernican-age impact crater well known for its high-albedo ejecta blanket and nearby flow features rich in pyroclastic materials. The Lyman Alpha Mapping Project (LAMP) is a far-ultraviolet (FUV) spectrograph (57–197 nm) on board the Lunar Reconnaissance Orbiter (LRO). LAMP data identified Aristarchus crater as having a high Off-band (155–184 nm) to On-band (130–155 nm) albedo (Off/On) ratio, providing new insight into the mineral composition of the area. Previous LAMP observations of bright crater rays and lunar swirls show that regions of high Off/On-band ratios may indicate highly feldspathic compositions. In this study we use LAMP data to understand FUV compositional signatures at Aristarchus. We investigate four well-characterized regions of interest around Aristarchus crater, and we compare Off/On-band ratios at Aristarchus crater to laboratory-derived ratios of several endmembers such as anorthite and olivine. We further analyze LAMP FUV spectra alongside near-infrared spectra from the Moon Mineral Mapper (M ^3 ) on board Chandrayaan-1 to characterize the mineralogy in several regions of interest. We find that LAMP Off/On-band ratios are able to distinguish between plagioclase feldspars and minerals such as quartz and mafic-dominated compositions. The LAMP Off/On-band ratios at Aristarchus are higher than previously reported ratios for plagioclase-rich regions, suggesting that the composition is unique to Aristarchus. Spectra from LAMP and M ^3 both show that the central peak and high-albedo ejecta around Aristarchus contain shocked, possibly alkalic, plagioclase feldspar.

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