17:15 〜 18:45
[PPS03-P05] High-resolution grinding tomography of calcium-aluminum-rich inclusions in Allende meteorite
キーワード：CAI、ダスト成長、ダスト破壊、隕石
The evolution process from dust (μm- to mm-scale) to planetesimal (m- to km-scale) in the protoplanetary disk is the key to forming the early Solar System. The efficiency of the evolution depends on the physical condition of the early Solar System, such as dust/gas ratio and turbulence. The coagulation process of the dust is limited by the fragmentation process caused by the high relative velocity [1].
Refractory inclusions, including Calcium-Aluminum-rich Inclusions (CAIs) and Amoeboid Olivine Aggregates (AOAs), have strong evidence to constrain the coagulation/fragmentation process in the Solar System. These inclusions were condensed from the gas in high-temperature regions (>~1600 K), formed as the first solid materials, transported to the formation region of chondrite parent bodies, and finally accreted to these bodies. The maximum size of refractory inclusions is relatively large (cm-scale) within chondrites. This is characteristic of the planetary formation model because rather large dust cannot avoid the fragmentation process and radially drift to the Sun. Mechanical and photometrical information, including refractory inclusions' size, color, and shape, is essential to constrain planetary dust's coagulation and fragmentation processes.
3D visualization of inclusions is a valuable step further to constrain the coagulation and fragmentation processes within refractory materials. Previous studies conducted 3D visualization to estimate the size distribution, modal abundance, and morphological information of refractory materials by the X-ray Computed Tomography (XCT) technique. The bright-field grinding tomography technique using a high-resolution optical camera was developed in the paleontology community [3], which is a straightforward way to assess the 3D information of CAIs. This study aims to constrain the coagulation and fragmentation history of the refractory materials in the early Solar System by the bright-field 3D grinding tomography for a low shock stage (S1) meteorite, Allende.
The process in the protoplanetary disk before the accretion to the asteroids can induce this fragmentation. One possibility is the dust collisional process occurred within the CAI formation region. Dust in the protoplanetary disk generally coagulates by the stickiness. However, the coagulation is limited by the collisional process with high relative velocities. This process likely explains the anisotropy of Material 004 surface. Also, this event occurred after the WL rim accretion.
Our observation for Materials 004 and 021 suggests the fragmentation event occurred before and after the WL rim accretion. This observation means that the CAI formation region's collisional process is effective in the coagulation and recycling phases. These collisional processes should occur within the residence time of CAI is <2000 yrs, whereas the coagulation timescale of CAI is 10–102 years [10]. The record of fragmentation of Material 021 suggests that the complete coagulation, collision, and rim accretion occur immediately. Also, the record of Material 004 suggests that the collisional process is still effective if the rim accretion is terminated.
The numerical simulation of coagulation of CAI precursors suggests that the cut-off in the large-size particles exists on the size distributions [10]. This result is interpreted as a “fragmentation barrier” because the fragmentation causes this cut-off. Charnoz et al. [10] demonstrated that the case for Vfrag (threshold radial velocity for fragmentation) = 1–10 m/s well reproduces the size distribution of CAIs in CV chondrite. The fragment size obtained in this study (Material 004; 2.2 mm3) is consistent with explaining this case.
Refractory inclusions, including Calcium-Aluminum-rich Inclusions (CAIs) and Amoeboid Olivine Aggregates (AOAs), have strong evidence to constrain the coagulation/fragmentation process in the Solar System. These inclusions were condensed from the gas in high-temperature regions (>~1600 K), formed as the first solid materials, transported to the formation region of chondrite parent bodies, and finally accreted to these bodies. The maximum size of refractory inclusions is relatively large (cm-scale) within chondrites. This is characteristic of the planetary formation model because rather large dust cannot avoid the fragmentation process and radially drift to the Sun. Mechanical and photometrical information, including refractory inclusions' size, color, and shape, is essential to constrain planetary dust's coagulation and fragmentation processes.
3D visualization of inclusions is a valuable step further to constrain the coagulation and fragmentation processes within refractory materials. Previous studies conducted 3D visualization to estimate the size distribution, modal abundance, and morphological information of refractory materials by the X-ray Computed Tomography (XCT) technique. The bright-field grinding tomography technique using a high-resolution optical camera was developed in the paleontology community [3], which is a straightforward way to assess the 3D information of CAIs. This study aims to constrain the coagulation and fragmentation history of the refractory materials in the early Solar System by the bright-field 3D grinding tomography for a low shock stage (S1) meteorite, Allende.
The process in the protoplanetary disk before the accretion to the asteroids can induce this fragmentation. One possibility is the dust collisional process occurred within the CAI formation region. Dust in the protoplanetary disk generally coagulates by the stickiness. However, the coagulation is limited by the collisional process with high relative velocities. This process likely explains the anisotropy of Material 004 surface. Also, this event occurred after the WL rim accretion.
Our observation for Materials 004 and 021 suggests the fragmentation event occurred before and after the WL rim accretion. This observation means that the CAI formation region's collisional process is effective in the coagulation and recycling phases. These collisional processes should occur within the residence time of CAI is <2000 yrs, whereas the coagulation timescale of CAI is 10–102 years [10]. The record of fragmentation of Material 021 suggests that the complete coagulation, collision, and rim accretion occur immediately. Also, the record of Material 004 suggests that the collisional process is still effective if the rim accretion is terminated.
The numerical simulation of coagulation of CAI precursors suggests that the cut-off in the large-size particles exists on the size distributions [10]. This result is interpreted as a “fragmentation barrier” because the fragmentation causes this cut-off. Charnoz et al. [10] demonstrated that the case for Vfrag (threshold radial velocity for fragmentation) = 1–10 m/s well reproduces the size distribution of CAIs in CV chondrite. The fragment size obtained in this study (Material 004; 2.2 mm3) is consistent with explaining this case.