A novel method for inversing FeO content from spectral absorption characteristics and maturity index using LSCC data

Abstract

Iron is one of the major elements on the Moon. In general, it exists in two forms, i.e. FeO and submicroscopic metallic iron (SMFe). The presence of FeO on the Moon is of great significance in studying the history of lunar lava differentiation and its evolution. However, it has been difficult to inverse the abundance of FeO from the spectral data of the Moon, since the two forms of iron have opposite optical effects on the spectral absorption characteristics of the lunar surface. The spectral absorption depth will be strengthened by FeO, while weakened by SMFe that is produced by space weathering. The FeO of the Moon is inversed either directly from reflectance spectra or spectral absorption characteristics of satellite, telescope and in-situ obtained spectra, both without taking into account the effect of space weathering, which may induce bias on the FeO inverse. The degree of space weathering can be expressed by various maturity indexes, such as magnetic maturity (e.g. Is and Is/FeO) and optical maturity (e.g. OMAT and continuum slope). To better quantitate the content of FeO from the lunar spectra, in this study, we first investigate the variations of spectral absorption depth and maturity indexes due to different degrees of space weathering using Hapke radiative transfer model. Then the correlation of different maturity indexes is analyzed. Based on these, to consider the optical effects of FeO and SMFe, a novel method to inverse the FeO from lunar spectra are established. By comparing the FeO derived with the new method with four methods proposed by others, the FeO derived in this study yields a better correlation with laboratory measured FeO contents using LSCC data.