Abstract. The physical evolution of the lunar surface with exposure to the space environment is termed maturation, and maturity is the degree to which a particular lunar soil possesses quantitative characteristics consistent with that exposure. Several quantitative measures or indices of maturity have been proposed and employed, including the abundance of solar wind gas, abundance of various types of agglutinates, va:'ious measures of grain size, and ls/FeO. Among the changes attendant with space exposure are striking changes in the optical characteristics of soils. Mature lunar soils are dark red and exhibit reduced spectral contrast relative to immature soils. This paper presents an optical maturity index that quantifies the spectral effects of maturation. We show that this optical maturity index correlates with other maturity indices about as well as the accepted maturity indices correlate among themselves and is only weakly coupled to composition. The modest correlations among maturity indices suggest important controls on individual maturity indices other than age, uncorrelated variations in the rates of accumulation of individual indicators, or variations in depths over which indicators are eraplaced. In addition to mixing, these efibcts conspire to reduce the equivalence of maturity and duration of surface exposure. Optical maturity illustrates some of these effects, showing that ejecta of large and small craters •nature at different rates and that the interiors and ejecta of large craters exhibit systematically different optical maturities. The same or analogous effects are likely to influence other maturity indices.

Abstract. The derivation of quantitative elemental concentrations from multispectral imaging of the Moon has long been a goal of lunar remote sensing. Concentration maps at the spatial resolutions available from the recent Clementinc mission would provide a revolutionary new tool for understanding the origin and evolution of the lunar crust. Lucey et al. [ 1995] presented a method for extracting the concentration of Fe from multispectral imaging of the Moon. This paper examines and quantifies important aspects of that technique left unexamined by Lucey et al. which had the potential to severely limit its utility. These aspects include the effects of maturity, grain size, mineralogy, shading due to topography, and the presence of glass. We also present a new algorithm for derivation of TiO2 from multispectral imaging of both mare and highland units. We f'md that both techniques are only weakly sensitive to maturity and that they have about 1 wt % accuracy based on examination of the spectral properties and compositions of resolved lunar sampling stations presented by Blewett et al. [ 1997]. We also discuss these f'mdings in the context of two contrasting views of the effect of composition on lunar spectral properties presented by Pieters and coworkers and Hapke and coworkers. We f'md the view of Hapke and coworkers to be more consistent with our observations. Using a global mosaic of Clementinc multispectral data and these element derivation algorithms, we find that the global modal abundance of FeO is 4.5 wt % ñ 1 wt % and the global modal abundance of TiO2 is 0.45 wt % ñ 1 wt. %.

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Abstract. Clementine UVVIS images of the lunar sample-return sites have been processed and used to produce refined calibrations for the iron and titanium determination algorithms of Lucey et al. [ 1995, 1996]. The high spatial resolution of the Clementine data permits individual sampling stations to be resolved at the Apollo 15, 16, and 17 landing sites. We find an excellent, linear correlation between the spectral Fe and Ti parameters and the average FeO and TiO2 contents of soils sampled at each site or station. This correlation demonstrates that these techniques can confidently be applied to other areas of the Moon. The Luna 24 site does not fit the Ti relation found for other sites, suggesting that either its sample is nonrepresentative or the reported landing coordinates are incorrect.

Abstract-Lunar mare basalt sample data suggest that there is a bimodal distribution of Ti02 concentrations. Using a refined technique for remote determination of Ti02, we find that the maria actually vary continuously from low to high values. The reason for the discrepancy is that the nine lunar sample return missions were not situated near intermediate basalt regions. Moreover, maria with 2-4 wt% Ti02 are most abundant, and abundance decreases with increasing Ti02. Maria surfaces with Ti02 >5 wt% constitute only 20% of the maria. Although impact mixing of basalts with differing Ti concentrations may smear out the distribution and decrease the abundance of high-Ti basalts, the distribution of basalt Ti contents probably reflects both the relative abundances of ilmenite-free and ilmenite-bearing mantle sources. This distribution is consistent with models of the formation of mare source regions as cumulates from the lunar magma ocean.