Iron and titanium abundance and maturity degree distribution on the lunar nearside

New digital images of the lunar nearside albedos at 0.42, 0.65, 0.75, and 0.95 mu m derived from telescopic data were used to map the abundance and distribution of iron, titanium, and maturity degree on the lunar nearside. Developing the approach by P. Lucey et al. (1995, Science 268, 1150), a method of separating contributions of the Fe and Ti abundance and maturity degree to spectral properties of the lunar surface is presented. The main objective of the method is an analysis of the 3D correlation diagram of optical characteristics of regolith material with the aim of choosing a coordinate system providing the best correlations of these characteristics with Fe and Ti abundance (data for the Surveyor, Luna, and Apollo landing sites) and with maturity degree (laboratory measurements of lunar samples by E. Fischer and C. Pieters (e.g., 1996, J. Geophys. Res. 101, 2225). To find the coordinates, a geometrical optics model of light scattering in particulate media enabling to calculate the absorption coefficient from albedo measurements is used. An analysis of the correlation diagram FeO-TiO2 provides two maps characterizing optical types of the lunar nearside. In particular, the maps show that the basalts of Mare Serenitatis and Mare Tranquillitatis are not widely extended on the lunar nearside. The maturity degree, parameter I-s/FeO, was also mapped. Regions with I-s/FeO less than or equal to 50 are young craters surrounded by ray systems, whereas the condition I-s/FeO greater than or equal to 70 corresponds to regions associated with Copernicus ejecta, western boundaries of Mare Tranquillitatis and Mare Serenitatis, and a portion of the south highland. The new map of FeO distribution on the lunar nearside was used to study a correlation between iron content and distribution of remanent magnetism over the lunar surface. The relationship obtained has a reverse behavior: the lower the iron content, the higher the magnetism. (C) 1999 Academic Press.