Petrographic and mineralogical characterization of asteroid (162173) Ryugu: The possible new ref-erence material for the Solar System element abundance

Following its formation at 4.5672 Ga (Amelin et al., 2002), the Solar System underwent chemical and isotopic fractionation that modified the primitive composition of the solar nebula. In order to under-stand the evolution of the Solar System, it is of significant importance to constrain its unmodified composition. Ivuna-type CI carbonaceous chondrites show a strong compositional match with the solar photosphere, suggesting that they represent the most pristine Solar System material (Holweger, 1977). For this reason, CI chondrites have been considered for decades the best candidate as reference material for the Solar System elemental abundance. Fragments from the C-type asteroid (162173) Ryugu, collected by the JAXA/Hayabusa2 mission (Watanabe et al., 2019), show strong chemical and mineralogical similarities with CI chondrites, but a negligible amount of terrestrial weathering (Yokoyama et al., 2022). Since terrestrial weathering may have led to chemical and isotopic modifications in CI chondrites, the asteroid Ryugu may represent a more pristine reference material for the Solar System element abundance, hence the importance of carrying out a full characterization of the returned samples. In this work, we present the results of a petrographic and mineralogical characterization carried out on two Ryugu particles by means of state-of-the-art analytical instrumentation, with the aim to con-tribute to the definition of the possible new standard material for future geochemical and cosmochemical studies.