Geochemical probing: comprehensive analyses of carbonaceous chondrites

  • Supervisors (*corresponding): Eizo Nakamura*, Katsura Kobayashi, Ryoji Tanaka, Tak Kunihiro, Hiroshi Kitagawa
  • Number of students: up to 6

Carbonaceous chondrites are characterized by abundant carbon up to 3wt% and unmelted-and-pristine nature.  To seek for the materials without later stage modification, Hayabusa 2 targets the C-type asteroid “Ryugu” that is considered to be the parent body of the carbonaceous chondrite.

The carbonaceous chondrites are mechanical mixture of objects with different origin, and its major constituent is ‘matrix’ consisting of micro-grains with typical size to be less than 1 µm.  The modal abundances of the matrix vary from 5% to 99% and random micro sampling of asteroid will likely result in collection of the matrix materials. Because of its gain size, major and trace elements distribution preserved on the grains in the matrix should reflect not only nebular condensation process but also asteroidal fluid-related process that are unique to each carbonaceous chondrite.

How one can reconstruct the original asteroid by increasing the quantity of materials to be analyzed?  Sensitivity, precision, and resolution of analytical techniques are not constant against the quantity.  During this program, the whole-rock carbonaceous-chondrites serve as parent bodies.  The matrix materials correspond to sub sample of the bodies.  What is the minimum quantity of the matrix materials to identify from which carbonaceous chondrites the materials are coming from?  Three carbonaceous chondrites will be studied focusing geochemical description of both whole rock and the matrix materials using destructive and non-destructive techniques. Students will simulate an initial analysis of the materials returned from Ryugu. During the program, you have chances to analyze carbonaceous chondrites by several techniques that include SEM, EPMA, SIMS, LA-ICPMS, ICPMS, TIMS, and TEM. Details of facilities to apply the project are available on the PML homepage (https://pml.misasa.okayama-u.ac.jp/).