Abstract
Cosmic dusts are classified into interplanetary dust particles (IDPs) and micrometeorites (MMs) depending on the sampling site. MMs similar to anhydrous IDPs and those with extremely rich in carbon (ultra carbon-rich micrometeorites: UCMMs) have been found from Antarctica, and they are considered as cometary origin as well as anhydrous IDPs. Lately, such MMs have been discovered from snow, which should have less hydrous alteration than in ice. These MMs are larger than IDPs and should have important information on the early stage of the solar system.In this study, 3-D structures of 39 MMs recovered from Antarctic snow were studied nondestructively using X-ray microtomography. The samples were imaged at beamline BL20XU and BL47XU in SPring-8 at 10keV. The effective spatial resolution was about 0.5 micrometers. 3-D binery images of the samples were obtained from the CT images, and their volumes and porosities were calculated. The samples were also observed by SEM, and analyzed by EDS and SR-based XRD. Distributions of mineral phases were also estimated from the linear attenuation coefficients of the CT images by considering the XRD results. By comparing these data, the MM samples were classified. For future work, a detailed study using TEM will be carried out after choosing typical samples.
