Fig. 5: Oxygen three-isotope plot showing the average composition of Ryugu particles in relation to the principal Solar System oxygen isotope reservoirs.

The composition of Sun and Solar Wind (SW)⁶², refractory solids⁶³ plot at the bottom left of CCAM/Y&R slope 1 lines. Matrix materials from Acfer 094, known as cosmic symplectites^47,48 and some interplanetary dust particles (IDPs)⁶⁴ plot at higher δ¹⁸O values along the slope 1 lines. On the scale of this diagram analyses from Ryugu, Earth and the inferred water composition from the Semarkona ordinary chondrite⁶⁵ plot close to the intersection of the TFL and slope 1 lines. Acfer 094 cosmic symplectites^47,48 analyses are thought to be representative of the oxygen isotope composition of primordial water ice. The composition of the Ryugu particles can be explained in terms of relatively extensive closed system exchange between ¹⁶O-poor fluids interpreted to have a composition similar to matrix materials from Acfer 094 (refs. ^47,48) and ¹⁶O-rich solids such as those commonly found in CC meteorites. This evidence appears to be at odds with the proposal that asteroid Ryugu is of cometary origin⁴⁴ (see main text for further discussion). Mixing lines are CCAM¹³ and Y&R⁶⁶, which is the Young and Russell Line.