Mapping iron in the lunar mare: An improved approach

Previous methods for mapping iron (Lucey et al., 1995, 1998, 2000a) give inconsistent results in terms of suppressing the effects of maturity, making it difficult to distinguish true units of contrasting iron from regions that simply show the residual effects of incomplete separation of maturity. These methods rely on an assumption that materials of similar iron content but varying maturity form radial trends on a plot of VIS reflectance versus NIR/VIS ratio. Recently, the assumption of radial behavior of maturity trends in mare regions has been called into question by Staid and Pieters (2000). They observed trends in the mare that appeared more parallel in nature. In this work we study nearly 10,000 craters in six mare regions and model the effects of maturity with radiative transfer theory to quantify and better understand the spectral behavior of maturity variations in the mare. We confirm that the maturity trends in mare regions are more parallel than radial, and we exploit this fact to develop a new algorithm for determination of iron content in mare regions. This new mare iron algorithm better compensates for maturity than previous methods, and uncertainties due to maturity variations are less than 0.5 wt% FeO. Absolute uncertainties are similar to previous algorithms (1.5 wt% FeO). Results from this work provide the ability to detect iron anomalies in the ejecta of craters and as a result more confidently map vertical stratigraphy in the lunar mare in terms of iron composition.