11:30 〜 11:45
[PPS08-10] SELENEスペクトルプロファイラが観測した月初期地殻形成時の水環境
★招待講演
キーワード：月の水、純粋斜長岩、近赤外分光
Water (OH and/or H2O) is highly volatile and possesses unique properties essential for developing life on Earth. The Moon preserves information about the early solar system, making it a crucial archive for studying the original water environment of the Earth–Moon system, which is difficult to access from Earth's geologically active surface. Recent data from remote sensing missions and advanced analytical techniques have revealed that the Moon contains much more water than previously believed.
This study aims to get insights into the water environment in the early phase of the Moon’s formation. Purest anorthosite (PAN) is a rock composed of more than 98 vol% plagioclase on the Moon, having formed during the early stages of lunar evolution, around 4.4 billion years ago. Therefore, the study of water in PAN is particularly important because it can provide crucial information about the early volatile content of the Moon. In this study, near-infrared spectral data from Spectral Profiler (SP) onboard SELENE was analyzed to detect water in PAN outcrops.
The SP offers near-infrared spectral data that allows detailed investigation of the distribution and state of water on the lunar surface. The SP data provides the highest wavelength resolution and signal-to-noise ratio among available near-infrared spectroscopic data covering the global lunar surface. In particular, measurements within the 512 nm–1644 nm range, which includes the weak water absorption band at 1.4–1.5 μm. Other orbital spectroscopic data have struggled to capture this weak absorption band, but the SP data’s low noise and high spectral resolution give it the potential to evaluate it. Furthermore, this wavelength range is unaffected by thermal emission from the lunar surface, allowing for a clear water distribution investigation without requiring thermal corrections.
As results, for 3% of the SP data for purest anorthosite outcrops, we identified a 1.5 μm spectral absorption feature, which suggests the presence of water. The band depths of identified absorptions showed variations under similar conditions. They were independent of local time. Their maximum values decreased with increasing exposure age. These results suggest that the water in some PAN outcrops was retained from the early lunar environment. This finding is the first evidence that some of the PAN were formed in wet magma. The variation in water content between previous studies and this study, and also our observed variations among different PAN outcrops suggest that lunar crust is highly heterogenous. For the melt from which the water-concentrated PAN formed was estimated to have contained from 1500 ppm a few wt% of water. This heterogeneity is likely influenced not only by the diversity of the parent magma but also by differences in degassing efficiency. The discovery of indigenous water in primitive PAN outcrops enhances our knowledge of the water conditions in the early Earth–Moon system and the initial stages of lunar evolution.
This study aims to get insights into the water environment in the early phase of the Moon’s formation. Purest anorthosite (PAN) is a rock composed of more than 98 vol% plagioclase on the Moon, having formed during the early stages of lunar evolution, around 4.4 billion years ago. Therefore, the study of water in PAN is particularly important because it can provide crucial information about the early volatile content of the Moon. In this study, near-infrared spectral data from Spectral Profiler (SP) onboard SELENE was analyzed to detect water in PAN outcrops.
The SP offers near-infrared spectral data that allows detailed investigation of the distribution and state of water on the lunar surface. The SP data provides the highest wavelength resolution and signal-to-noise ratio among available near-infrared spectroscopic data covering the global lunar surface. In particular, measurements within the 512 nm–1644 nm range, which includes the weak water absorption band at 1.4–1.5 μm. Other orbital spectroscopic data have struggled to capture this weak absorption band, but the SP data’s low noise and high spectral resolution give it the potential to evaluate it. Furthermore, this wavelength range is unaffected by thermal emission from the lunar surface, allowing for a clear water distribution investigation without requiring thermal corrections.
As results, for 3% of the SP data for purest anorthosite outcrops, we identified a 1.5 μm spectral absorption feature, which suggests the presence of water. The band depths of identified absorptions showed variations under similar conditions. They were independent of local time. Their maximum values decreased with increasing exposure age. These results suggest that the water in some PAN outcrops was retained from the early lunar environment. This finding is the first evidence that some of the PAN were formed in wet magma. The variation in water content between previous studies and this study, and also our observed variations among different PAN outcrops suggest that lunar crust is highly heterogenous. For the melt from which the water-concentrated PAN formed was estimated to have contained from 1500 ppm a few wt% of water. This heterogeneity is likely influenced not only by the diversity of the parent magma but also by differences in degassing efficiency. The discovery of indigenous water in primitive PAN outcrops enhances our knowledge of the water conditions in the early Earth–Moon system and the initial stages of lunar evolution.