¹Megha Bhatt, ¹Urs Mall, ²Christian Wöhler, ²Arne Grumpe, ¹Roberto Bugiolacchi
¹Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Straße 2, 37191 Katlenburg-Lindau, Germany
²Image Analysis Group, Dortmund University of Technology,Otto-Hahn Str.4,44227 Dortmund, Germany

The FeO weight percentage (wt.%) abundance of the Moon’s western nearside (View the MathML source55°S-55°N and View the MathML source5°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 et al., 2012) 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 et al., 2014) 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 FeO wt.% map (Lucey et al., 2000). The effects of topography and space weathering on FeO wt.% 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 3-4 wt.% less FeO for the ray system of Tycho than for the surrounding region. The average iron abundance for the lunar highlands is about 6 wt.% and for the mare regions is about 16 wt.% 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 FeO wt.% is in the range 20-24 wt.% for the high-Ti basalts using both the modified iron abundance estimation and the regression-based elemental abundance estimation algorithms.

Reference
Bhatt M, Mall U, Wöhler C, Grumpe A, Bugiolacchi R (2014) A Comparative study of iron abundance estimation methods: application to the western nearside of the moon. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.10.023]

Copyright Elsevier

¹Amy Bonsor, ¹Zoë M. Leinhardt, ¹Philip J. Carter, ²Tim Elliott, ²Michael J. Walter, ³Sarah T. Stewart
¹School of Physics, H.H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK
²School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK
³Department of Earth and Planetary Sciences, University of California, Davis, One Shields Avenue, Davis, California 95616, USA

Several lines of evidence indicate a non-chondritic composition for Bulk Earth. If Earth formed from the accretion of chondritic material, its non-chondritic composition, in particular the super-chondritic 142Nd/144Nd142Nd/144Nd and low Mg/Fe ratios, might be explained by the collisional erosion of differentiated planetesimals during its formation. In this work we use an N-body code, that includes a state-of-the-art collision model, to follow the formation of protoplanets, similar to proto-Earth, from differentiated planetesimals (> 100 km) up to isolation mass (> 0.16 M⊕). Collisions between differentiated bodies have the potential to change the core-mantle ratio of the accreted protoplanets. We show that sufficient mantle material can be stripped from the colliding bodies during runaway and oligarchic growth, such that the final protoplanets could have Mg/Fe and Si/Fe ratios similar to that of bulk Earth, but only if Earth is an extreme case and the core is assumed to contain 10% silicon by mass. This may indicate an important role for collisional differentiation during the giant impact phase if Earth formed from chondritic material.

Reference
Bonsor A, Leinhardt ZM, Carter PJ, Elliott T, Walter MJ, Stewart ST (2014) A collisional origin to earth’s non-chondritic composition? Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.10.019]

Copyright Elsevier