6:15 PM - 7:30 PM
[PPS23-P10] Features of 3D shapes of lunar regolith particles: comparison with Itokawa particles and experimental impact fragments
Keywords:Apollo mission, Luna mission, Hayabusa mission, X-ray tomography, SPring-8
In the present study, in addition to the Apollo samples (10084 and 60501), we used Luna samples; L1613-3 (Luna 16: Mare Fecunditatis), L2001-4 (Luna 20: Apollonius Highlands) and L24130.3-2,3,4 (Luna 24: Mare Crisium). The sample particles were attached on a toothpick with double-sided tape to take CT images at once by X-ray microtomography. Imaging experiments were made at BL20B2 of SPring-8 with the X-ray energies of 17.9, 18.1 or 20 keV and voxel size of 1.73 um. Particles were extracted by binarization. The isolated particles having more than 10,000 voxels, which are possible for significant 3D shape measurement , were analyzed. So far, we have examined 156 and 90 particles of 10084 and L2001-4, respectively.
The axial lengths of particles were measured by ovoid approximation (OA) and bounding box (BB) method . In BB method, the axial lengths differ if the order of determination of the shortest, intermediate and longest lengths (S, I and L, respectively) is different. We adopted two methods, where S was determined first followed by I and L corresponding to the impact fragments of  and L was determined first followed by I and S corresponding to . The axial ratios, I/L and S/I, were plotted as Zingg diagrams. These 3D shape distributions were compared with the previous data of lunar regolith particles [3,4], Itokawa particles  and experimental impact fragments [2,5,6] using Kolmogolov-Smilnov (K-S) test.
There is no significant difference between the particle shape distributions of the same sample with different imaging methods (grain by grain or many particles at once) at least for 10084. As far as the samples analyzed and the previous samples concerned, there are basically no significant differences of the shape distributions among lunar samples irrespective of mare and highland samples. In contrast, the lunar particles are more spherical than the Itokawa particles and the experimental impact fragments. Because residence time scale of particles in lunar regolith is long (the order of one billion years) , it is possible for lunar regolith particles to become spherical by abrasion due to gardening. We are planning to report the results of more samples in the presentation.
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