¹Tetsuya Yokoyama et al. (>10)
Science 379, 6634 Link to Article [DOI: 10.1126/science.abn78]
¹Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan.
Reprinted with permission from AAAS

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 measured the mineralogy and bulk chemical and isotopic compositions of Ryugu samples. The samples are mainly composed of materials similar to those of 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, about 5.2+0.8−0.7 million (statistical) or 5.2+1.6−2.1
million (systematic) years after the 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 that of the Sun’s photosphere than other natural samples do.