In order to understand the regolith processes occurring on small asteroids such as Itokawa, it is essential to investigate noble gases of solar wind (SW) origin and cosmogenic noble gases produced by galactic cosmic ray (GCR) bombardment in the regolith materials. The SW and GCR-produced noble gas compositions represent dynamic gardening processes occurring on the asteroid's surface such as migration of the grains in regolith and their residence time on the asteroidal surface. For this purpose, we have reported SW noble gases and GCR produced noble gases on Hayabusa samples as an initial investigation and the 1st A/O, showing short cosmic ray exposure ages, SW implantation ages, and migration of the grains in Itokawa’s surface layer.
Following the above mentioned results, the objectives of this study as the 2nd A/O are 1) to estimate life time of regolith particles on the Itokawa surface based on GCR-produced cosmogenic noble gases such as 3He and 21Ne, 2) to estimate duration of solar wind (SW) implantation to individual regolith grains, 3) to compare a depth profile of implanted SW-He at the grain surface measured with a probe analysis with a release profile of SW-He measured with stepwise heating of bulk grain, and 4) to detect trapped Kr and Xe in the Hayabusa samples. To fulfill these requirements, we would like to request relatively large sample(s) containing olivine which is preferable because Mg in olivine is the main target element producing cosmogenic 21Ne by GCR bombardment.