Mathematics – Logic
Scientific paper
Jan 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999nvm..conf....6c&link_type=abstract
Workshop on New Views of the Moon 2: Understanding the Moon Through the Integration of Diverse Datasets, p. 6
Mathematics
Logic
Iron Oxides, Lunar Crust, Lunar Maria, Lunar Surface, Mineralogy, Regolith, Titanium Oxides, Thorium, Gamma Ray Spectrometers, Lunar Prospector, Clementine Spacecraft
Scientific paper
The Clementine mission (CLM) produced global multispectral data that resulted in a map of FeO and Ti02 concentrations of the lunar surface. The recent Lunar Prospector (LP) mission returned the first global data for the distribution of surface abundances of key elements in lunar rocks, using a gamma-ray spectrometer (GRS) and neutron spectrometer(NS). Integrating CLM mineralogical spectral reflectance and LP chemical data is important to enhance our view of lunar crust origin and evolution, lunar volcanism, and surface processes. Iron, Ti, and Th having relatively large compositional variation over the lunar surface, as well as strong isolated peaks in the GRS spectra, information concerning the distribution and concentration of these elements has been derived from maps of corrected (cosmic ray, nonsymmetric response of the instrument) counting rates only, without converting them into absolute abundances. Maps produced contain count rates in equal-area projection averaged into 5 x 5 degrees latitude/longitude bins, from -90 to +90 degrees latitude and -180 to +180 degrees longitude. In this work, we have used the CLM global FeO and Ti02 abundances (wt%) maps converted at the LP spatial resolution (about 150 km/pixel) to produce FeO and TiO2 GRS abundance maps, through a linear regression based on the analysis of the scatter distribution of both datasets. The regression coefficients have been determined from the data taken between -60 and +60 degrees latitude to avoid uncertainties in the CLM spectral data due to nonnominal conditions of observation at high latitudes. After a critical assessment of the validity of these coefficients for every class of absolute abundance, the LP data have been transformed into absolute abundances for the whole Moon. The Th LP data have been converted into abundances (ppm) using Th concentrations in average soils from the Apollo and Luna sites given. Values of Th abundances for these samples range between 0.5 and 13 ppm. A nonlinear regression has been applied to the LP data, except for low count rate values (corresponding to Th abundances below 1.27 ppm) for which a first-order linear regression has been applied. Statistical tests demonstrate that the Lunar Prospector FeO, TiO2, and Th abundances estimates we have produced through the regressions are reliable. For the LP maps, the uncertainty of absolute FeO and Ti02 estimates is on the same order as that for CLM, i.e., 2 and 1.5 wt% respectively. For the Th, abundance estimates, the uncertainty is about 1-2 ppm. At first order, our global FeO and Ti02 abundances maps from LP are in very good agreement with those obtained from CLM. The Th abundance map is also in good agreement with a recent global Th abundance map, although concentrations have a higher range (0-20 ppm) in our case, and may be slightly overestimated. However, a more detailed comparison between CLM and LP abundance maps of FeO and Ti02 reveals regional differences. Differences between the two datasets are expected because of instrumental and observational causes (spatial resolution, depth of observation), but also because they are sensitive to different types of information (mineralogy vs. chemistry). Maps of differences in abundances between LP and CLM data have been produced for both FeO and Ti02. In relation to the precision of the LP and CLM data, we consider that differences between the two datasets exceeding 2 wt% are significant. Concerning FeO contents, differences up to 4-5 wt% are observed in the South Pole Aitken Basin, and generally at high latitude (up to 70 degrees) in the southern hemisphere, as well as in the northern border (Iridum-Gruithuisen domes region) and the southern border (Sinus Aestum) of the Imbrium Basin. Most important differences, up to 6-7 wt%, are found in Mare Serenitatis, Crisium, and Fecunditatis. Concerning Ti02, most important differences (4-5 wt%) between LP and CLM abundances are located within Mare Tranquillitatis. Differences (about 2-3 wt%) also occur in the northern border of the Imbrium Basin (Ir-Gruithuisen domes region) and in the western part of Oceanus Procellarum (from southwest of Kepler, up to the Aristarchus Plateau). Regions for which differences in FeO and/or Ti02 content may arise from the presence of heterogeneous terrains due to geological transitions at the scale of observation of LP have been identified on the basis of the spatially degraded FeO and Ti02 CLM maps. These regions correspond to Mare Crisium, the western part of Procellarum, and Mare Humorum. The surface heterogeneity effect cannot be invoked in the case of the South Pole Aitken (SPA) Basin interior and its immediate vicinity. However, LP indicates a lower content in FeO than CLM (8-11 wt% vs. 11-13 wt% respectively). This observation suggests that the SPA materials may contain a lower proportion of Fe than was previously thought. This may imply a smaller proportion of mantle materials excavated during the impact event than predicted in and give some constraints to the models of large basin formation, Some regions such as Mare Serenitatis, Tranquillitatis, Fecunditatis, and Crisium do present significant differences in FeO and Ti02 abundances, the LP estimates being lower than the CLM ones. This might be ascribed to a different perception of the influence of the mare regolith reworking by the LP geochemical observation, sensitive to the subsurface regolith, and the CLM reflectance spectroscopy observation, sensitive to the surface mineralogy. Original document contains more information.
Barreau G.
Chevrel Serge D.
Daydou Yves
Feldman William C.
Maurice Sylestre
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