Any surfaces of atmosphere-less bodies exposed to interplanetary space have their structures, optical properties, chemical compositions and mineralogy gradually changed by irradiation, implantation, and sputtering by solar wind, galactic cosmic ions, electrons, UV and X-rays, and bombardment by micrometeorites. Information on the space weathering experienced by asteroid is gathered through reflectance spectroscopy acquired through ground-based or onboard spectrometers. Hayabusa grains, sampled at the surface of the S-type Itokawa asteroid, offer a unique perspective to get insights on the early stages of asteroidal space weathering.
In particular, our scientific objective is to understand how the optical properties of asteroidal surfaces are influenced by the microstructure of the thin processed layer of the regolith grains. To achieve this goal, we are planning on (i) acquiring the Vis-NIR reflectance spectra of individual Hayabusa particles, and (ii) imaging the surface modifications induced by space weathering by TEM technique on the same individual grains. Raman and mid-IR micro-spectroscopy will also be applied to gather additional information on olivine (e.g. elemental composition, degree of amorphisation/crystallization...).
The interpretation of this analytical work will be strengthened by an experimental approach that will consist on irradiations and post-characterization of terrestrial olivine and of a LL5 chondrite.