This is a subsequent proposal of the same title of international AO2 research by our group. In the AO2, we have conducted in-situ three-dimensional (3D) distribution of solar wind He for three Itokawa samples. A clear 3D distribution of solar wind He with tens nm resolution was observed from the RA-QD02-0169, but we could not characterize the topography and texture of the measurement region because the sample was lost during transportation to SEM analysis after SNMS analysis. From the other two samples (RA-QD02-0178 and RB-QD04-0055), fluences of solar wind irradiation were one order of magnitude less than those from the RA-QD02-0169. Such large variability of solar wind fluences by Matsumoto et al. (2018), i.e., less than 50% of samples experienced few or little solar wind irradiation. Therefore, we need to continue further measurements from other samples after we return the samples of AO2.
The research plan is essentially the same as our AO2 proposal with some improvements. (1) the samples characterize mineralogy and petrology of surfaces by SEM. (2) We determine in-situ distribution of solar wind Ne in addition to solar wind He. Using these results, we clarify ion implantation process and discuss space-weathering histories of asteroid Itokawa.
If this distribution is clarified, we can reveal (1) energy distribution of solar wind during about recent thousand years, (2) how many large CME occurred in the recent thousand years (3) how much noble gas escaped from the sample, and (4) what mechanism assist the noble gas escape.