―Establishing a data infrastructure to accurately determine the ilmenite content in the lunar maria through remote sensing―
Researchers) Geological Survey of Japan (GSJ), MATSUOKA Moe, Researcher, YAMAMOTO Satoru, Research Group Leader
Recently, the Moon, the most accessible celestial body from Earth, has garnered increasing attention as a realistic industrial base. Lunar basalt is enriched in ilmenite, which can be used to yield water, oxygen, iron, and titanium. These materials are essential for constructing bases on the lunar surface and sustaining human activity there.
Ilmenite is distributed across the lunar surface, but its precise distribution remains unclear. Understanding this is essential for developing resources on the Moon, including selecting candidate sites for building a lunar base. Ilmenite is also scientifically significant. Since formation and evolution of the Moon are not fully understood, ilmenite within the basalt, which is one of the major minerals on the lunar surface such as the lunar maria, records information about the Moon's interior. Ilmenite holds the key to revealing the composition of lunar magma and elucidating the Moon's formation and evolution processes.
Although remote sensing analysis of reflectance spectral data is a powerful method for determining ilmenite distribution on the lunar surface, challenges remain. First, it was suggested that even trace amounts of ilmenite mixed with other minerals could significantly impact the near-infrared reflectance spectra of mixed rocks. However, its spectral characteristics have not yet been elucidated, either qualitatively or quantitatively elucidated. Furthermore, existing ilmenite identification indices based on hyperspectral data could be improved in terms of quantitative accuracy due to the insufficient precision of the experimental verification data used to construct the indices. Their measurable concentration range was narrow, making them impractical for real-world applications.
Researchers at AIST have prepared data to more accurately estimate the ilmenite (FeTiO3, iron titanium oxide) content on the lunar surface.
Ilmenite present on the lunar surface is positioned as a critical resource for supporting human activities on the Moon because it can yield water, oxygen, iron, and titanium. While the distribution of ilmenite on the lunar surface is heterogeneous, the extent of its distribution remains unclear. Understanding this distribution is crucial for developing resources on the Moon, such as selecting candidate sites for lunar base construction. One powerful means of understanding ilmenite distribution is analyzing hyperspectral data obtained by lunar exploration satellites. However, ilmenite's spectral characteristics significantly change depending on its mixing ratio with other major constituent minerals, which makes it difficult to accurately estimate its content using conventional analysis methods.
To replicate lunar regolith containing ilmenite, we conducted an experiment where ilmenite and pyroxene were mixed, both of which were ground to particle sizes equivalent to those found on the Moon. We then obtained reflectance spectral data from this mixture. We analyzed the spectral data by precisely controlling the ilmenite-to-pyroxene mass ratio down to 1 % or less and varying the mixture ratio in up to 25 steps from 0 % to a maximum of 50 %. This analysis clarified the spectral characteristics of mixtures containing ilmenite. Concurrently, we conducted morphological observations and chemical composition analyses of the experimental samples to establish a reliable data foundation for effective spectral data analysis in lunar exploration.
Utilizing these results will enhance the accuracy of estimating ilmenite content through the analysis of hyperspectral data from lunar exploration satellites, which will contribute to the advancement of lunar resource development.