Carbonaceous meteorites are thought to be fragments of C-type (carbonaceous) asteroids. Samples of the C-type asteroid (162173) Ryugu were retrieved by the Hayabusa2 spacecraft. We measure the mineralogy, bulk chemical and isotopic compositions of Ryugu samples. They are mainly composed of materials similar to carbonaceous chondrite meteorites, particularly the CI (Ivuna-type) group. The samples consist predominantly of minerals formed in aqueous fluid on a parent planetesimal. The primary minerals were altered by fluids at a temperature of 37 ± 10°C, 5.2 − 0.8 + 0.7 (Stat.) − 2.1 + 1.6 (Syst.) million years after formation of the first solids in the Solar System. After aqueous alteration, the Ryugu samples were likely never heated above ~100°C. The samples have a chemical composition that more closely resembles the Sun’s photosphere than other natural samples do.

Northwest Africa (NWA) 6704 is a unique achondrite characterized by a near-chondritic major element composition with a remarkably intact igneous texture. To investigate the origin of this unique achondrite, we have conducted a combined petrologic, chemical, and 187 Re-187 Os, O, and Ti isotopic study. The meteorite consists of orthopyroxene megacrysts (En 55-57 Wo 3-4 Fs 40-42 ; Fe/Mn = 1.4) up to 1.7 cm in length with finer interstices of olivine (Fa 50-53 ; Fe/Mn = 1.1-2.1), chromite (Cr# ~ 0.94), awaruite, sulfides, plagioclase (Ab 92 An 5 Or 3 ) and merrillite. The results of morphology, lattice orientation analysis, and mineral chemistry indicate that orthopyroxene megacrysts were originally hollow dendrites that most likely crystallized under high supersaturation and super-cooling conditions (1-10 2 °C/h), whereas the other phases crystallized

Knowledge of planetary differentiation is crucial for understanding the chemical and thermal evolution of terrestrial planets. The 176 Hf radioactive decay system has been widely used to constrain the timescales and mechanisms of silicate differentiation on Earth, but the data interpretation requires accurate estimation of Hf isotope evolution of the bulk Earth. Because both Lu and Hf are refractory lithophile elements, the isotope evolution can be potentially extrapolated from the present-day 176 Hf radioactive decay system is a powerful tool to study planetary silicate differentiation and offers a unique means of examining the origin of the Earth's earliest crust (1-12). To allow for the correct interpretation of Lu−Hf data, however, the Hf isotope growth curve of the bulk Earth must be firmly established. On the basis of the refractory lithophile nature of both Lu and Hf, the Lu−Hf isotope composition of chondrites has been proposed as a reference for the composition of the bulk Earth and its silicate portion (13-15). However, the present-day 176

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