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Description:

C-type asteroids, which make up a significant portion of the main belt asteroids, are
believed to be composed of materials similar to CI and CM carbonaceous chondrites.
In this study, we conducted shock recovery experiments on Orgueil CI and CI affinity
Yamato 980115 CY (partly dehydrated CI) chondrites to examine their mineralogical
and textural changes under impact conditions. Our results indicate that weak shock
pressures below ~4 GPa do not produce significant shock metamorphic features,
supporting the current interpretation that most Ryugu grains experienced shock
pressures within this range. Above ~4 GPa, dehydration and degassing of Mg-Fe
phyllosilicates and carbonaceous materials become dominant, leading to rock
exfoliation. Rock melting begins above ~10 GPa, forming frothy layers composed of
iron-rich amorphous material. These findings suggest that the regolith layer of asteroid
Ryugu was primarily formed by the reassembly of rock fragments exfoliated by impacts
without undergoing strong shock metamorphism. However, highly shocked materials
may be buried beneath the regolith layer, highlighting the need for further
investigations into the interior composition of C-type asteroids to better understand
their thermal and impact histories.

Rights:

• Creative Commons BY-NC Attribution-NonCommercial 4.0 International
  

Keyword: CI chondrite, Impact process, Shock experiment, Shock metamorphism, Asteroid Ryugu

Date published: 2025-07-26

Publisher: Elsevier BV

Journal:

• Earth and Planetary Science Letters (ISSN: 0012821X) vol. 668 119559

Funding:

Manuscript type: Author's version (Accepted manuscript)

MDR DOI: https://doi.org/10.48505/nims.5726

First published URL: https://doi.org/10.1016/j.epsl.2025.119559

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Updated at: 2025-09-03 09:24:31 +0900

Published on MDR: 2025-09-03 12:20:33 +0900