5:15 PM - 7:15 PM
[PPS07-P07] Identification of Constituent Minerals in Antarctic Micrometeorites Based on Micro-FTIR Analysis
Extraterrestrial materials collected on Earth that are 2 mm or smaller in diameter are called cosmic dust. Cosmic dust includes Interplanetary Dust Particles (IDPs) collected from the stratosphere [1] and Antarctic Micrometeorites (AMMs) contained in snow and ice in Antarctica about 1 per kg [2]. IDPs were classified based on their mid-infrared absorption spectra characteristics during the 1970s and 1980s [3]. This study aims to measure the infrared absorption spectra of AMMs that exhibit mineralogical characteristics similar to those of IDPs [4], identify their primary mineral species, and compare them with the minerals observed in asteroids and cometary nuclei through astronomical observations to estimate the origins of cosmic dust.
In this study, 370 kg of surface snow collected around the Dome Fuji Station by the 59th and 60th Japanese Antarctic Research Expeditions was melted and filtered in a clean booth at Kyoto University. The same snow was sublimated on a Teflon sheet at the National Institute of Polar Research. Residual microparticles from these filters and sheets were extracted using a micromanipulator, arranged on gold sample holders, and subjected to SEM-EDS observation for AMM identification. Samples that did not show effects from aqueous alteration or heating were selected for analysis.
Infrared micro-spectroscopy was performed on nine AMMs, fine-grained matrices from Murchison CM2 chondrite, Orgueil CI chondrite, Allende CV3 chondrite, Tarda C2-ungrouped chondrite, and Tagish Lake C2-ungrouped chondrite, and standard samples (forsterite, orthoenstatite, clinoenstatite, two types of synthetic amorphous silicates simulating GEMS (glass with embedded metal and sulfide), and amorphous silicates with forsterite and enstatite compositions). Due to the extremely small particle size of AMMs, comparably sized samples were prepared for other materials.
Specific sample preparation is necessary for performing infrared micro-spectroscopy on micro-scale samples [5]. In this study, AMM samples were compressed and spread to 3 µm or less thickness using a diamond press. The spread samples were then transferred onto 10 mm diameter KBr pellets by pressing the diamond plates onto smooth synthetic sapphire plates. The same preparation process was applied to other samples to maintain consistent analytical conditions. These samples were analyzed using mapping analysis of mid-infrared absorption spectra (650–4000 cm-1) at SPring-8 BL43IR. Additionally, bulk mid-infrared absorption spectra in a broader wavelength range (350–4000 cm-1) were measured using a JASCO FTIR-4X installed in a nitrogen-purged glove box.
Some results of AMMs obtained from µ-FT-IR in the silicate characteristic wavelength range (8–13 µm) are presented. The standard samples, forsterite and enstatite, exhibited their strongest peaks at approximately 11.2 µm and 9.2 µm, respectively. Most of the analyzed AMMs were fine-grained and porous, with many exhibiting strong peaks at one or both of these wavelengths. These fine-grained porous AMMs were easily distinguishable from the matrices of aqueous-altered meteorites such as Tarda and Orgueil, which showed a strong peak at approximately 9.9 µm corresponding to the Si–O stretching vibration of layered silicates in their infrared absorption spectra. This suggests that these fine-grained porous AMMs have undergone minimal aqueous alteration. Furthermore, mapping analysis revealed the heterogeneous distribution of minerals within the AMM samples.
Future work will involve conducting bulk analyses of each AMM and meteorite matrix over a broader wavelength range using the FT-IR spectrometer in the glove box to derive more precise mineralogical compositions from their spectra.
[1] Bradley, (2014), Treatise on Geochemistry. Elsevier, pp. 287-308. [2] Noguchi et al., (2025), Meteorit & Planetary Science maps.14324 [3] Sandford and Walker, (1985), ApJ 291, 838. [4] Noguchi et al., (2015), Earth and Planetary Science Letters, 410, 1-11. [5] Raynal et al., (2000), Planetary and Space Science, 48, 1329-1339.
In this study, 370 kg of surface snow collected around the Dome Fuji Station by the 59th and 60th Japanese Antarctic Research Expeditions was melted and filtered in a clean booth at Kyoto University. The same snow was sublimated on a Teflon sheet at the National Institute of Polar Research. Residual microparticles from these filters and sheets were extracted using a micromanipulator, arranged on gold sample holders, and subjected to SEM-EDS observation for AMM identification. Samples that did not show effects from aqueous alteration or heating were selected for analysis.
Infrared micro-spectroscopy was performed on nine AMMs, fine-grained matrices from Murchison CM2 chondrite, Orgueil CI chondrite, Allende CV3 chondrite, Tarda C2-ungrouped chondrite, and Tagish Lake C2-ungrouped chondrite, and standard samples (forsterite, orthoenstatite, clinoenstatite, two types of synthetic amorphous silicates simulating GEMS (glass with embedded metal and sulfide), and amorphous silicates with forsterite and enstatite compositions). Due to the extremely small particle size of AMMs, comparably sized samples were prepared for other materials.
Specific sample preparation is necessary for performing infrared micro-spectroscopy on micro-scale samples [5]. In this study, AMM samples were compressed and spread to 3 µm or less thickness using a diamond press. The spread samples were then transferred onto 10 mm diameter KBr pellets by pressing the diamond plates onto smooth synthetic sapphire plates. The same preparation process was applied to other samples to maintain consistent analytical conditions. These samples were analyzed using mapping analysis of mid-infrared absorption spectra (650–4000 cm-1) at SPring-8 BL43IR. Additionally, bulk mid-infrared absorption spectra in a broader wavelength range (350–4000 cm-1) were measured using a JASCO FTIR-4X installed in a nitrogen-purged glove box.
Some results of AMMs obtained from µ-FT-IR in the silicate characteristic wavelength range (8–13 µm) are presented. The standard samples, forsterite and enstatite, exhibited their strongest peaks at approximately 11.2 µm and 9.2 µm, respectively. Most of the analyzed AMMs were fine-grained and porous, with many exhibiting strong peaks at one or both of these wavelengths. These fine-grained porous AMMs were easily distinguishable from the matrices of aqueous-altered meteorites such as Tarda and Orgueil, which showed a strong peak at approximately 9.9 µm corresponding to the Si–O stretching vibration of layered silicates in their infrared absorption spectra. This suggests that these fine-grained porous AMMs have undergone minimal aqueous alteration. Furthermore, mapping analysis revealed the heterogeneous distribution of minerals within the AMM samples.
Future work will involve conducting bulk analyses of each AMM and meteorite matrix over a broader wavelength range using the FT-IR spectrometer in the glove box to derive more precise mineralogical compositions from their spectra.
[1] Bradley, (2014), Treatise on Geochemistry. Elsevier, pp. 287-308. [2] Noguchi et al., (2025), Meteorit & Planetary Science maps.14324 [3] Sandford and Walker, (1985), ApJ 291, 838. [4] Noguchi et al., (2015), Earth and Planetary Science Letters, 410, 1-11. [5] Raynal et al., (2000), Planetary and Space Science, 48, 1329-1339.