Lunar Mare Soils: Space weathering and the major effects of surface-correlated nanophase Fe

Lunar soils farm the "ground truth" far calibration and modeling of reflect ance spectra for quantitative remote sensing. The Lunar Soil Characterizati on Consortium, a group of lunar sample and remote sensing scientists, has u ndertaken the extensive task of characterization of lunar soils, with respe ct to their mineralogical and chemical makeup. This endeavor is aimed at de ciphering the effects of space weathering of soils from the Moon, and these results should apply to other airless bodies. Modal abundances and chemist ries of minerals and glasses in the < 45 tm size fractions of nine selected mare soils have been determined, along with the bulk chemistry of each siz e fractions and their I-S/FeO values: These data can be addressed at http:/ web.utk.edu/similar to pgi/data.html. As grain size decreases, the bulk com position of each size fraction continuously changes and approaches the comp osition of the agglutinitic glasses: Past dogma had it that the majority of the nanophase Fe-0 resides in the agglutinitic glasses. However, as grain size of a soil decreases, the percentage of the total iron present as nanop hase-sized Fe (0) increases dramatically, while the agglutinitic glass cont ent rises only slightly. This is evidence for a large contribution to the I -S/FeO values from surface-correlated nanophase Fe-0, particularly in the < 10 p,m size fraction. This surficial nanophase Fe-0 is present largely as vapor-deposited patinas on the surfaces of almost every particle of the mat ure oils. It is proposed that these vapor-deposited, nanophase Fe-0-bearing patinas may have far greater effects upon reflectance spectra of mare soil s than the agglutinitic Fe-0.