New results and implications for lunar crustal iron distribution using sensor data fusion techniques

Remote measurements of the Moon have provided iron maps, and thus essential constraints for models of lunar crustal formation and mare basalt petrogenesis. A bulk crustal iron map was produced for the equatorial region from Apollo gamma-ray (AGR) spectrometer measurements, and a global iron variation map from recent Clementine spectral reflectance (CSR) measurements. Both iron maps show bimodal distribution, but have significantly different peak values and variations. In this paper, CSR data have been recalibrated to pyroxene in lunar landing site soils. A residual iron map is derived from the difference between AGR (bulk) and recalibrated CSR (pyroxene) iron abundances. The most likely interpretation is that the residual represents ferrous iron in olivine. This residual iron is anticorrelated to basin age, with older basins containing less olivine, suggesting segregation of basin basalt sources from a progressively fractionating underlying source region at the time of basin formation. Results presented here provide a quantitative basis for (1) establishing the relationship between direct geochemical (gamma-ray, X-ray) and mineralogical (near-IR) remote sensing data sets using sensor data fusion techniques to allow (2) simultaneous determination of elemental and mineralogical component distribution on remote targets and (3) meaningful interpretation of orbital and ground-based spectral reflectance measurements. When calibrated data from the Lunar Prospector mission are available, mapping of bulk crustal iron and iron-bearing soil components will be possible for the entire Moon. Similar analyses for data from the Near Earth Asteroid Rendezvous (NEAR) mission to asteroid 433 Eros will constrain models of asteroid formation.