Decoding Lunar Surface Chemistry from Class: One Flare at a Time

DECODING LUNAR SURFACE CHEMISTRY FROM CLASS: ONE FLARE AT A TIME. S. Adak1*, N. S. Pillai2, D. Dhingra1 and S. Narendranath2, 1Department of Earth Sciences, Indian Institute of Technology Kanpur, Uttar Pradesh, 208016, India ([email protected], [email protected]), 2Space Astronomy Group, U R Rao Sattelite Centre, ISRO, ISITE campus, Bengaluru, Karnataka, 560037, India ([email protected], [email protected]) Introduction: Understanding the geochemical framework of the Moon requires robust elemental datasets. The Chandrayaan-2 Large Area Soft X-ray Spectrometer (CLASS) is utilizing principles of solar-induced x-ray fluorescence (XRF) to measure the elemental abundance of major and minor elements on the lunar surface [1]. CLASS builds upon the legacy of Chandrayaan-1 X-ray Spectrometer (C1XS), with enhanced sensitivity, improved spatial resolution, and expanded elemental detection capability [1, 2]. The scientific usefulness of CLASS derived elemental maps depends not only on the quality of the instrument and data acquisition framework but also on the rigor of spectral modeling, accuracy of solar flux calibration, and interpretation of results incorporating the geologic context. CLASS has been mapping the abundance of major elements (Mg, Al, Si, Fe and Ca), and volatile elements (Na and O) [3, 4]. Scientific Motivation: We are using CLASS data to generate elemental abundance maps of the Tranquillitatis-Serenitatis region. It is a key region on the Moon exhibiting compositional contrast in the basalts. Further, we have samples from two lunar missions which visited this region, namely, Apollo11 and Apollo 17. The sample information provides a strong context for the interpretation of remote sensing observations from the area. Results & Discussion: Maps of various elements have been generated using an established data processing pipeline [1]. We show here the preliminary version of the elemental maps of aluminium and magnesium for the region (Figure 1). The maps seem to suggest higher abundance of aluminium and moderate abundance of magnesium in Serenitatis basalts when compared with the basalts in Tranquillitatis. The detailed trends would be more apparent once full coverage of both regions are collated. Similar maps for other elements are also being generated. A key impediment to the detailed interpretation of these maps is their spatial resolution. As additional datasets are being acquired, the maps will become better due to enhanced signal to noise ratio as well as better geographical coverage. We will present details of the dataset, its processing and new results from the analysis of Tranquilliatis-Serenitatis region. Summary: High quality elemental maps of Tranquillitatis-Serenitatis region, derived from CLASS payload onboard Chandrayaan-2, are being developed. Full coverage maps will enable robust evaluation of compositional diversity of this scientifically interesting region on the Moon. Figure 1 Preliminary Al and Mg abundance maps of Serenitatis-Tranquillitatis region from CLASS. Acknowledgements: ISRO Chandrayaan-2 AO Project, CLASS payload team, CSIR Ph.D. fellowship to SA. References: [1] Pillai et al. (2021) Icarus, 363, 114436. [2] Narendranath et al. (2011) Icarus, 214, 53-66. [3] Narendranath et al. (2022) ApJL, 937, L23 [4] Narendranath et al. (2024) Icarus, 410, 115898.