Abundant presolar grains and primordial organics preserved in carbon-rich exogenous clasts in asteroid Ryugu

Preliminary analyses of asteroid Ryugu samples show kinship to aqueously altered CI (Ivuna-type) chondrites, suggesting similar origins. We report identification of C-rich, particularly primitive clasts in Ryugu samples that contain preserved presolar silicate grains and exceptional abundances of presolar SiC and isotopically anomalous organic matter. The high presolar silicate abundance (104 ppm) indicates that the clast escaped extensive alteration. The 5 to 10 times higher abundances of presolar SiC (similar to 235 ppm), N-rich organic matter, organics with N isotopic anomalies (1.2%), and organics with C isotopic anomalies (0.2%) in the primitive clasts compared to bulk Ryugu suggest that the clasts formed in a unique part of the protoplanetary disk enriched in presolar materials. These clasts likely represent previously unsampled outer solar system material that accreted onto Ryugu after aqueous alteration ceased, consistent with Ryugu's rubble pile origin.

Automated summary

Preliminary analyses of asteroid Ryugu samples show its kinship to aqueously altered CI chondrites, suggesting similar origins. C-rich primitive clasts in Ryugu samples contain preserved presolar silicate grains and exceptional abundances of presolar SiC and isotopically anomalous organic matter. The high presolar silicate abundance indicates minimal alteration, and the significantly higher abundances of presolar SiC, N-rich organic matter, and isotopically anomalous organics in the primitive clasts suggest a unique formation in a presolar material-enriched region of the protoplanetary disk.