Three‐dimensional shapes and Fe contents of Stardust impact tracks: A track formation model and estimation of comet Wild 2 coma dust particle densities |
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| Authors: | Yosuke IIDA Akira TSUCHIYAMA Toshihiko KADONO Kanako SAKAMOTO Tomoki NAKAMURA Kentaro UESUGI Tsukasa NAKANO Michael E ZOLENSKY |
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| Institution: | 1. Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka 560‐0043, Japan;2. Institute of Laser Engineering, Osaka University, Suita 565‐0871, Japan;3. Department of Earth and Planetary Science, Faculty of Sciences, Kyushu University, Hakozaki, Fukuoka 812‐8581, Japan;4. Synchrotron Radiation Research Institute, SPring‐8, Sayo, Hyogo 679‐5198, Japan;5. Geological Survey of Japan, Advanced Industrial Science and Technology, Tsukuba 305‐8567, Japan;6. Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, Texas 77058, USA |
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| Abstract: | Abstract– We investigated three‐dimensional structures of comet Wild 2 coma particle impact tracks using synchrotron radiation (SR) X‐ray microtomography at SPring‐8 to elucidate the nature of comet Wild 2 coma dust particles captured in aerogel by understanding the capture process. All tracks have a similar entrance morphology, indicating a common track formation process near the entrance by impact shock propagation irrespective of impactor materials. Distributions of elements along the tracks were simultaneously measured using SR‐XRF. Iron is distributed throughout the tracks, but it tends to concentrate in the terminal grains and at the bottoms of bulbs. Based on these results, we propose an impact track formation process. We estimate the densities of cometary dust particles based on the hypothesis that the kinetic energy of impacting dust particles is proportional to the track volume. The density of 148 cometary dust particles we investigated ranges from 0.80 to 5.96 g cm?3 with an average of 1.01 (±0.25) g cm?3. Moreover, we suggest that less fragile crystalline particles account for approximately 5 vol% (20 wt%) of impacting particles. This value of crystalline particles corresponds to that of chondrules and CAIs, which were transported from the inner region of the solar system to the outer comet‐forming region. Our results also suggest the presence of volatile components, such as organic material and perhaps ice, in some bulbous tracks (type‐C). |
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