Based on the initial analysis of Hayabusa samples, Itokawa particles are classified to “poorly equilibrated” and “highly equilibrated” particles, and it has been suggested that “poorly equilibrated” particles are related to LL4 chondrites, and “highly equilibrated” ones are related to LL5 and LL6 chondrites (Nakamura et al., 2011). It should be noted that, in addition to LL3 to LL6 chondrites, there are certain numbers of LL chondrites assigned as LL7 chondrites which have similar bulk composition to other LL chondrites but completely recrystallized or experienced small degree of melting. Although no Itokawa particle similar to LL7 chondrites has been reported so far, the highly equilibrated texture and their mineral compositions suggest that some of them can be related to LL7 chondrites.
Therefore, it is important to link Itokawa particles to equilibrated LL chondrites in order to understand the evolution history of primitive asteroids. Previously, we have studied 48 Antarctic LL chondrites and showed that there are compositional changes in silicate and metal during thermal metamorphism from LL4 to LL7. In this study, we will examine the mineralogical and crystallographic characteristics of Itokawa particles caused by thermal metamorphism, and compare their mineralogy to equilibrated LL chondrites. Because highly equilibrated LL chondrites can be a transitional between chondrites and primitive achondrites, systematic study of the metamorphic grade of Itokawa particles will provide the valuable information for the metamorphism on the chondrite parent body and the earliest stages of igneous evolution of planetestimals in our solar system.