4:45 PM - 5:00 PM
[PPS07-05] High spatial resolution three-color CT imaging of CM and CI meteorites and their heated samples for a rehearsal analysis of Ryugu
Keywords:Hayabusa 2, Ryugu, nano XCT
JAXA's spacecraft "Hayabusa2" returned to Earth last December, and curation of samples collected from the asteroid "Ryugu" is ongoing. Based on the analysis of reflectance spectra and other data, Ryugu is thought to be composed of weakly heated CM and/or CI meteorite-like materials [1]. Since the microstructure of such materials is complex on the sub-micron scale, three-dimensional observations with high spatial resolutions are useful to understand the formation process of the Ryugu samples. Our group is planning to perform XCT analysis of the Ryugu samples at SPring-8 BL47XU, and are preparing for the analysis.
As the rehearsal of the sample analysis, we conducted nano-XCT observations (~70 nm/pixel) of CM and CI meteorites and their heated samples using monochromatic X-rays. The samples were fixed to the top of a Ti needle by FIB or to a carbon fiber using resin. Images of X-ray absorption coefficient (LAC) were obtained at energies of 7.00 and 7.35 keV, which are in between the K-edge of energy of Fe. Images of X-ray refractive index decrement (RID) were also obtained by a one-dimensional scanning X-ray microscope at 8.00 keV [2]. By registration of the three kinds of images, a three-dimensional image as quasi-color image in which each pixel has three variables (LAC of 7.00 keV, LAC of 7.35 keV, and RID of 8.00 keV) was obtained. The 7.00 keV images were segmented using the Chan-Vase method to quantitatively measure particle shapes and porosities.
A comparison of the unheated Murchison meteorite and the sample heated to 400 °C for X hours shows that part of the TCI (tochilinite-cronstedtite intergrowth) is magnetized. Furthermore, at 600 °C X hours, the matrix and TCI reacted. In the Murray meteorite, the TCI of the sample heated at 600 °C for 1 hour retained its shape, but some of it reacted with the matrix.
A comparison of an unheated CI meteorite (the Orgueil meteorite) with its heated sample at 500 °C for 50 hours showed that a lip-shaped structure (~5 µm long) of Fe-rich serpentine that was universally observed in the unheated sample was slightly shrunken and detached from the matrix in the heated sample although there were not serious textual changes in its matrix and magnetite. This lip-shaped structure may be a good indicator to constrain the heating conditions for weak thermal metamorphism of CI meteorites[h1] .
[1] Kitazato et al., Science 364, 272–275 (2019)
[2] Takeuchi et al., J. Synchrotron Radiat. 20, 793–800 (2013).
As the rehearsal of the sample analysis, we conducted nano-XCT observations (~70 nm/pixel) of CM and CI meteorites and their heated samples using monochromatic X-rays. The samples were fixed to the top of a Ti needle by FIB or to a carbon fiber using resin. Images of X-ray absorption coefficient (LAC) were obtained at energies of 7.00 and 7.35 keV, which are in between the K-edge of energy of Fe. Images of X-ray refractive index decrement (RID) were also obtained by a one-dimensional scanning X-ray microscope at 8.00 keV [2]. By registration of the three kinds of images, a three-dimensional image as quasi-color image in which each pixel has three variables (LAC of 7.00 keV, LAC of 7.35 keV, and RID of 8.00 keV) was obtained. The 7.00 keV images were segmented using the Chan-Vase method to quantitatively measure particle shapes and porosities.
A comparison of the unheated Murchison meteorite and the sample heated to 400 °C for X hours shows that part of the TCI (tochilinite-cronstedtite intergrowth) is magnetized. Furthermore, at 600 °C X hours, the matrix and TCI reacted. In the Murray meteorite, the TCI of the sample heated at 600 °C for 1 hour retained its shape, but some of it reacted with the matrix.
A comparison of an unheated CI meteorite (the Orgueil meteorite) with its heated sample at 500 °C for 50 hours showed that a lip-shaped structure (~5 µm long) of Fe-rich serpentine that was universally observed in the unheated sample was slightly shrunken and detached from the matrix in the heated sample although there were not serious textual changes in its matrix and magnetite. This lip-shaped structure may be a good indicator to constrain the heating conditions for weak thermal metamorphism of CI meteorites[h1] .
[1] Kitazato et al., Science 364, 272–275 (2019)
[2] Takeuchi et al., J. Synchrotron Radiat. 20, 793–800 (2013).