Itokawa particles are the first regolith samples from "rubble-pile" asteroid that clearly witness multiple processes over a 4.6 billion-year period. A series of elaborate studies [e.g. Nakamura et al. 2011] revealed that Itokawa had suffered from complex history such as (1) intense thermal metamorphism around the 800-900 degree, (2) catastrophic collision and disaggregation, (3) reaccretion onto rubble-pile asteroid, and (4) space weathering. However, the chronology of Itokawa and its parent body is not well understood.
In order to decipher the history recorded in Itokawa particles, we have conducted the investigation of U-Pb systematics of phosphates in Itokawa particles using NanoSIMS. For the AO2 proposal, two polished sections of RA-QD02-0056, RA-QD02-0031 and one pristine particle of RB-CV-0025 are allocated for us from JAXA, and we successfully obtained not only the 4.6 Ga crystallization age but also the shock age of billion years ago (Now, under review of Nature communication). For better understanding of the impact history of the Itokawa (tighter constrain on the impact age and/or multi-or-single impact events billions years ago), further analysis is required. So, we request two polished sections and one pristine grain that are expected to include phosphates by X-ray CT and/or SEM-EDS analysis.