A novel method for lunar elemental abundance estimation using Chandrayaan-2 class and Chandrayaan-1 M3 data

Abstract

We report the first employment of the Chandryaan-2 Large Area Soft X-ray Spectrometer (CLASS) data [1] from Chandrayaan-2 mission as ground truth to estimate SiO2, Al2O3, and MgO for understanding the petrological characteristics of the Moon. The algorithm uses multivariate regression between CLASS derived elemental abundances from selected regions spread over mare and highlands and spectral parameters derived using the nearly global coverage of the Moon obtained by the Moon Mineralogy Mapper (M3) [2]. Spectral parameters derived from the two pronounced absorption bands around 1 µm and 2 µm are sensitive to mineral composition [3] and space-weathering effects [4]. We used the same set of M3 spectral parameters as proposed in [5] that is robust with respect to the effects of soil maturity. The M3 spectral parameters have been extracted corresponding to the CLASS footprint size of 12.5 x 12.5 km2. The CLASS derived elemental abundances primarily rely on enhanced solar activity without any dependencies on empirical relationships to lunar returned samples and refer to the top most layer of regolith as M3. We present a first set of global SiO2, Al2O3, and MgO maps constructed by applying a multivariate linear regression (MLR) model to the CLASS footprints and a M3 global mosaic of 20 pixels per degree resolution [5, 6]. The M3 global reflectance mosaic is derived using the framework in [6]. The results are based on a comparative analysis considering independent techniques [5, 7, 8] applied on regional and global scales. We found that the absolute values of CLASS derived MgO matches well with the technique of [5] and also at Apollo landing sites. The absolute values in the case of SiO2 and Al2O3 systematically differ when compared to [5]. The absolute values will be refined and FeO, TiO2, and CaO maps will be derived once a higher coverage of CLASS footprints is available. References: [1] Pillai N. S. et al. (2021) Icarus 363, 114436. [2] Pieters C. M. et al. (2009) Current Science 96, 500-505; [3] Burns R., Remote geochemical analysis: Elemental and mineralogical composition (1993); [4] Morris, R.V. (1978) Lunar Planet. Sci. Conf. Proc., pp. 2287-2297; [5] Bhatt M. et al. (2019) A&A 627, A155. [6] Wöhler, C. et al. (2017) Science Advances 3, e1701286. [7] Lucey P. G. et al. (2000) JGR 105, 20297-20306; [8] Bhatt M. et al. (2015) Icarus 248, 72-88.