Constraints on Solar System early evolution by MicrOmega analysis of Ryugu carbonates

The samples returned from a C-type asteroid (Ryugu) by the Hayabusa2 mission constitute unprecedented access to carbonaceous material never exposed to Earth’s atmosphere that may still contain phases formed in the earliest stages of the Solar System. We present an extensive analysis of a large set of grains and bulks of the Ryugu samples, performed directly within the Japan Aerospace Exploration Agency Curation Center in Japan with the near-infrared hyperspectral microscope MicrOmega, to identify and characterize the carbonate component of the samples, which has recorded early evolutionary steps. We reveal a large presence of carbonates within the collection distributed over two main size-dependent populations: generally small (<100 µm) dolomite-rich and larger (up to hundreds of µm) breunnerite-rich areas, some with complex elongated morphologies. Similarities with C-chondrites suggest that such characteristics may emerge as a general property of primitive materials in the outer part of the asteroid belt. These two carbonate populations likely translate distinct processes and stages of formation in the early Solar System that might have taken place while CO 2 ice was still present (possibly before accretion of the Ryugu parent body) and/or from C-rich phases.