ひとさじのイルメナイトと輝石の混合実験－月の海に眠るイルメナイトの含有量をリモートセンシングで正確に知るためのデータ基盤を整備－

2026-02-24 産業技術総合研究所

図1 輝石にイルメナイトを混合した時の反射スペクトルの変化。特にイルメナイトが少量（質量比が<9 ％）のとき、反射率の減少が顕著であることがわかる。800 nmから850 nmの波長領域は分光計の検出器切り替えに起因する強度変動が見られるため、グラフから除外した。
※原論文の図を引用・改変したものを使用しています。

＜関連情報＞

• https://www.aist.go.jp/aist_j/press_release/pr2026/pr20260224_2/pr20260224_2.html
• https://iopscience.iop.org/article/10.3847/PSJ/ae3746

イルメナイト混合物のUV-Vis-NIR反射スペクトル：月の海域におけるTiO 2含有量推定への示唆 UV–Vis–NIR Reflectance Spectra of Ilmenite Mixtures: Implications for Estimation of TiO2 Content in Lunar Mare Regions

Moe Matsuoka and Satoru Yamamoto
The Planetary Science Journal  Published: 2026 February 24
DOI:10.3847/PSJ/ae3746

Abstract

We performed spectral measurements on mixtures of ilmenite powder (<48 μm) and clinopyroxene or gabbro powder (<155 μm) to investigate the effect of ilmenite content on the spectral characteristics in the ultraviolet (UV), visible (Vis), and near-infrared (NIR) ranges. We found that increasing ilmenite content leads to (1) a darkening of Vis and NIR reflectance, (2) a decrease of the UV slope, (3) a weakening of band depths around 950–1050 nm and 1250–1300 nm, and (4) a neutralization of the Vis–NIR slope. For lunar mare regions, which have ∼7wt% ilmenite, it was estimated that the albedo in the Vis–NIR reflectance would decrease by 25%–29%, the Vis–NIR slope would decrease by 9%–26%, and the UV slope would decrease by 4%–5%. We also examined the effect of the addition of clinopyroxenes and gabbro on the spectral characteristics of ilmenite. The results indicate that most diagnostic features of ilmenite were masked, except for a distinct peak near 900 nm, which can thus serve as a reliable indicator of the presence of ilmenite in mixed compositions. Furthermore, we evaluated existing methods for estimating TiO₂ content in lunar mare regions using spectral band ratios. The results indicate that ratios that incorporate UV reflectance are more sensitive to ilmenite content than those that incorporate reflectance only at Vis and/or NIR wavelengths longer than 415 nm. This suggests that UV reflectance is more reliable for the estimation of ilmenite abundance on the lunar surface.