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.

The extraterrestrial materials returned from asteroid (162173) Ryugu consist predominantly of low-temperature aqueously formed secondary minerals and are chemically and mineralogically similar to CI (Ivuna-type) carbonaceous chondrites. Here, we show that high-temperature anhydrous primary minerals in Ryugu and CI chondrites exhibit a bimodal distribution of oxygen isotopic compositions: 16 O-rich (associated with refractory inclusions) and 16 O-poor (associated with chondrules). Both the 16 O-rich and 16 O-poor minerals probably formed in the inner solar protoplanetary disk and were subsequently transported outward. The abundance ratios of the 16 O-rich to 16 O-poor minerals in Ryugu and CI chondrites are higher than in other carbonaceous chondrite groups but are similar to that of comet 81P/Wild2, suggesting that Ryugu and CI chondrites accreted in the outer Solar System closer to the accretion region of comets.

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We developed a transportable micro‐XRF (µ‐XRF) spectrometer using a polycapillary X‐ray focusing half lens, which was placed between the sample and the detector. The total weight of the developed spectrometer was about 2 kg; its dimensions were 18(W) × 26(D) × 40(H) cm. The spatial resolution of the spectrometer with the half lens of a working (focal) distance of 30 mm was 171 µm at Fe Kα, which was evaluated by a wire scanning method. In this setup, it is easy to replace the polycapillary X‐ray half lens with one having a different analytical performance, because a precise position‐adjustment of the X‐ray lens is not required. The spacial resolution with the half lens of a working distance of 16 mm was 106 µm at Fe Kα. Depending on analyzing area on the sample and required spatial resolution, we can easily change the X‐ray lens, as in a conventional optical microscope. The calibration curves of V, Cr, Mn, and Ni measured for standard steel materials showed good linear relationships (correlation coefficients >0.993). Clear elemental mapping could be obtained by scanning the sample (Cu mesh). An elemental analysis of a micro‐region in an electronic device was also performed by the transportable µ‐XRF spectrometer. Sn and Pb were detected at the metallic part (Sn–Pb solder) of the device. Br and Ba were observed at some resin parts of the electronic device. Copyright © 2009 John Wiley & Sons, Ltd.

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