A comparative study of iron abundance estimation methods: Application to the western nearside of the Moon

Abstract

The FeO weight percentage (wt.%) abundance of the Moon’s western nearside (55°S–55°N and 5°E–40°W) is estimated using data from the InfraRed Spectrometer-2 (SIR-2) and the Moon Mineralogy Mapper (M3). In this study, we modified an FeO abundance estimation algorithm (Bhatt, M., Mall, U., Bugiolacchi, R., McKenna-Lawlor, S., Banaszkiewicz, M., Nathues, A., Ullaland, K. [2012]. Icarus 220, 51–64) which relies exclusively on the 2-μm absorption band parameters. The modified FeO abundance estimation algorithm and the regression-based elemental abundance estimation algorithm (Wöhler, C., Grumpe, A., Berezhnoy, A., Bhatt, M.U., Mall, U. [2014]. Icarus 235, 86–122) which is based on the 1-μm and 2-μm absorption band parameters is applied to the M3 data. We have compared results obtained from these two modified algorithms with a previously published Clementine’s FeOwt.% map (Lucey, P.G., Blewett, D.T., Jolliff, B.L. [2000]. J. Geophys. Res. 105, 20297–20306). The effects of topography and space weathering on FeOwt.% estimates have been successfully minimized using the modified algorithm based on the 2-μm absorption band parameters. Thus, this algorithm can be successfully applied at middle to high latitudes. Furthermore, a correction for TiO2 is applied to the FeO abundance estimation algorithm based on the 2-μm absorption band parameters using the M3 data. Our comparative study shows a good correspondence between the three algorithms discussed. There are two locations: the crater Tycho and the region around Rima Bode which show major discrepancies. Our modified algorithm based on the 2-μm absorption parameters predicts 3–4wt.% less FeO for the ray system of Tycho than for the surrounding region. The average iron abundance for the lunar highlands is about 6wt.% and for the mare regions is about 16wt.% using the regression-based elemental abundance estimation algorithm and the algorithm based on the 2-μm absorption parameters. This result is consistent with the previous analysis using Lunar Prospector Gamma-Ray Spectrometer data sets. The FeOwt.% is in the range 20–24wt.% for the high-Ti basalts using both the modified iron abundance estimation and the regression-based elemental abundance estimation algorithms.