4:00 PM - 4:15 PM
[PPS08-21] Measurement of Apollo moon regolith samples using a visible and near-infrared micro-spectroscopy camera
Keywords:moon, regolith, spectroscopy
Reflectance spectroscopy has been widely utilized in planetary exploration to investigate various celestial bodies. In particular, visible and near-infrared spectroscopy is a useful method for determining the distribution of minerals on planetary surfaces, as it prominently reveals mineral absorption features. For example, olivine exhibits an absorption band near 1 μm, while pyroxene has absorption bands around 1 μm and 2 μm (e.g., Adams, 1974; Pieters, 1983).
Continuous spectrometers are widely used in planetary exploration. These instruments offer high spectral resolution but low spatial resolution, meaning only averaged spectra over a broad area can be obtained. In contrast, the Multiband Imager (MI) aboard the lunar orbiter "Kaguya" achieved relatively high spatial resolution (20 m for visible wavelengths and 62 m for near-infrared) through multiband spectroscopy (Ohtake et al., 2008). The MI is an effective observation instrument as it enables efficient exploration of wide areas from an altitude of 100 km above the lunar surface. However, it lacks the capability to identify minerals at the microscopic scale, such as those in regolith.
Future exploration missions require spectral measurements with higher spatial resolution (on the order of cm to mm or less). This study develops a multiband spectroscopic instrument with a high-resolution near-infrared camera and explores data acquisition and analysis methods.
The spectroscopic instrument consists of a vertically adjustable sample stage, with incident light set at 30° and a camera positioned directly above the sample (0°). A halogen lamp was used as the light source, and bandpass filters allowed illumination in 13 specific wavelength bands: 550, 750, 850, 900, 950, 990, 1000, 1050, 1100, 1150, 1200, 1250, and 1550 nm, within the range of 550–1500 nm. The camera detected wavelengths from visible to near-infrared and was equipped with a high-magnification lens with a zoom range of 0.77x to 9.31x. Using this instrument, measurements were conducted on lunar return samples (Apollo 17, 70161), anorthosite samples, and lherzolite samples.
The measurements revealed an absorption feature at 1250 nm in the anorthosite sample and at 1050 nm in the lherzolite sample. Additionally, in the Apollo 17 sample(70161), a 1 μm absorption band associated with anhydrous silicate minerals was observed. Furthermore, mineral particles that appeared white to the naked eye exhibited an absorption feature around 1250 nm, similar to that observed in the anorthosite sample.
Next, the Fe content in the minerals was estimated using the ratio of reflectance at 750 nm(R750) and 950 nm (R950), based on the following equation proposed by Lucey et al. (1995):
θFe = arctan{[(R950/R750)-1.25]/(R750-0.037)}
wt% FeO = 20.527 × θFe – 12.266
As a result, the FeO content of regolith derived from lunar mare basalt was estimated to be around 15 wt%. This value is generally consistent with the elemental composition of Apollo 70161 sample published in the NASA database. In contrast, the mineral particles that appeared white to the naked eye were estimated to contain little to no Fe (~0 wt%).
The findings suggest the presence of anorthosite-like particles in lunar regolith derived from mare basalt, contributing to geological interpretations of the lunar surface. The Apollo 17 landing site was in the Taurus-Littrow Valley, located on the southeastern rim of the Serenitatis Basin (Schmitt, 1973). Anorthosite from nearby highlands may have been deposited through geological processes. The high spatial resolution of this spectroscopic instrument enables such detailed geological assessments, demonstrating the potential of high-resolution visible-near-infrared microscopic spectroscopy. The developed instrument is expected to be a valuable tool for future planetary exploration missions.
Continuous spectrometers are widely used in planetary exploration. These instruments offer high spectral resolution but low spatial resolution, meaning only averaged spectra over a broad area can be obtained. In contrast, the Multiband Imager (MI) aboard the lunar orbiter "Kaguya" achieved relatively high spatial resolution (20 m for visible wavelengths and 62 m for near-infrared) through multiband spectroscopy (Ohtake et al., 2008). The MI is an effective observation instrument as it enables efficient exploration of wide areas from an altitude of 100 km above the lunar surface. However, it lacks the capability to identify minerals at the microscopic scale, such as those in regolith.
Future exploration missions require spectral measurements with higher spatial resolution (on the order of cm to mm or less). This study develops a multiband spectroscopic instrument with a high-resolution near-infrared camera and explores data acquisition and analysis methods.
The spectroscopic instrument consists of a vertically adjustable sample stage, with incident light set at 30° and a camera positioned directly above the sample (0°). A halogen lamp was used as the light source, and bandpass filters allowed illumination in 13 specific wavelength bands: 550, 750, 850, 900, 950, 990, 1000, 1050, 1100, 1150, 1200, 1250, and 1550 nm, within the range of 550–1500 nm. The camera detected wavelengths from visible to near-infrared and was equipped with a high-magnification lens with a zoom range of 0.77x to 9.31x. Using this instrument, measurements were conducted on lunar return samples (Apollo 17, 70161), anorthosite samples, and lherzolite samples.
The measurements revealed an absorption feature at 1250 nm in the anorthosite sample and at 1050 nm in the lherzolite sample. Additionally, in the Apollo 17 sample(70161), a 1 μm absorption band associated with anhydrous silicate minerals was observed. Furthermore, mineral particles that appeared white to the naked eye exhibited an absorption feature around 1250 nm, similar to that observed in the anorthosite sample.
Next, the Fe content in the minerals was estimated using the ratio of reflectance at 750 nm(R750) and 950 nm (R950), based on the following equation proposed by Lucey et al. (1995):
θFe = arctan{[(R950/R750)-1.25]/(R750-0.037)}
wt% FeO = 20.527 × θFe – 12.266
As a result, the FeO content of regolith derived from lunar mare basalt was estimated to be around 15 wt%. This value is generally consistent with the elemental composition of Apollo 70161 sample published in the NASA database. In contrast, the mineral particles that appeared white to the naked eye were estimated to contain little to no Fe (~0 wt%).
The findings suggest the presence of anorthosite-like particles in lunar regolith derived from mare basalt, contributing to geological interpretations of the lunar surface. The Apollo 17 landing site was in the Taurus-Littrow Valley, located on the southeastern rim of the Serenitatis Basin (Schmitt, 1973). Anorthosite from nearby highlands may have been deposited through geological processes. The high spatial resolution of this spectroscopic instrument enables such detailed geological assessments, demonstrating the potential of high-resolution visible-near-infrared microscopic spectroscopy. The developed instrument is expected to be a valuable tool for future planetary exploration missions.