Primitive planetary materials are key to understand origin and evolution of our Solar System. Extraterrestrial materials such as meteorites are valuable samples that record information of the early solar system. Primitive extraterrestrial materials contain a wide variety of organic matter including amino acids, and most of them are complex macromolecular organic matter (known as insoluble organic matter, IOM) that do not have a defined molecular structure. The organic matter has formed and evolved at various stages of the solar system formation, such as molecular clouds, protoplanetary disks, and small bodies — some of them may have become raw materials for origin of life. In particular, aqueous alteration and thermal metamorphism in the small bodies — the final evolutionary stage of planetary materials — could be the most important stages that determine the final form of organic matter. Classical methods to analyze trace organics in meteorites are solvent extraction and acid demineralization. The spatial contexts, however, were lost by these methods. To understand chemical and physical processes of organic matter, fine scale observations of planetary materials are mandatory, including morphology and spatial relationship between organics and minerals. We applied the sub micrometer analytical techniques including atomic force microscope-based infrared spectroscopy (AFM-IR), scanning transmission X-ray microscopy/X-ray absorption near edge structure (STXM/XANES), and nanoscale secondary ion mass spectrometry (NanoSIMS), to the unique organic-rich clast found in the Zag meteorite. Ultra-thin sectioning of a sample particle using sulfur-embedded ultramicrotomy allows us to analyze almost identical areas of the sections on a TEM grid for STXM/XANES and these on a BaF2 window for AFM-IR and NanoSIMS. Coupled AFM-IR and NanoSIMS analysis on 15x15 µm zones of ultra-thin section of the Zag clast allows to study the spatial correlations at the sub-micron scale between the IR signatures at 1020 and 1740 cm-1 and the corresponding D/H isotopic composition of the sample. We are optimizing the methodology for further analyses of planetary materials aiming to develop the organic petrology to understand the chemical and physical processes of organic matter, as well as for analysis of asteroidal samples from Hayabusa2 mission.

Coordinated analysis using AFM-IR, STXM/XANES and NanoSIMS for “organic petrology” in complex planetary materials

ACS Spring Meeting 2021

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