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PI : Hisayoshi Yurimoto

Title : Space weathering analysis of Itokawa particles by in-situ three dimensional noble gas distribution using novel sputtered neutral mass spectrometry

Abstract

We determine in-situ distribution of solar wind He and try to measure other solar wind noble gases of individual Itokawa particles. Subsequently the particles characterize mineralogy, petrology and crystallinity of surfaces. A bulk noble gas composition and release pattern with increasing temperature of a particle are measured by noble gas mass spectrometer. Using these results, we clarify ion implantation effects for space weathering phenomena and discuss space-weathering history of asteroid Itokawa. Determination of noble gas corresponding micro-structure of solids has not been succeeded so far. We have newly developed new generation sputtered neutral mass spectrometry capable to detect tens ppma He from ~50 nm area on solid surface. This project will be figured out how distribute He (and other noble gases and H) in the surface layer of Itokawa particles with tens nm resolution. If this distribution is clarified, we can apply atomic mechanisms in solid clarified by mineralogy and crystallography, such as diffusion, partitioning, etc., to the noble gas cosmochemistry. As a result, behavior of noble gas in solid can be discussed as the same manner of trace element behavior. Therefore, this project is the first step to pioneer a new research field of noble gas mineralogy or noble gas astromineralogy.

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