Petrologic subtypes of CM chondrites: Reinvestigation and proposal of subtypes 3.0 to 2.8

The Tenth Symposium on Polar Science/Poster presentations: [OA] Antarctic meteorites, Wed. 4 Dec. / Entrance Hall (1st floor), National Institute of Polar Researc

Evidence for Impact Shock Melting in CM and CI Chondrite Regolith Samples

C class asteroids frequently exhibit reflectance spectra consistent with thermally metamorphosed carbonaceous chondrites, or a mixture of phyllosilicate-rich material along with regions where they are absent. One particularly important example appears to be near-Earth asteroid 1999 JU3, the target of the Hayabusa II sample return mission [1], although not all spectra indicate this. In fact most spectra of 1999 JU3 are featureless, suggesting a heterogeneous regolith. Here we explore an alternative cause of dehydration of regolith of C class asteroids - impact shock melting. Impact shock melting has been proposed to explain some mineralogical characteristics of CB chondrites, but has not been considered a major process for hydrous carbonaceous chondrites. What evidence is there for significant shock melting in the very abundant CMs, or less abundant but still important CI chondrites

Y-791498 and A-881828: The least-altered CR chondrites in NIPR Antarctic meteorite collection.

The Tenth Symposium on Polar Science/Special session: [OA] Antarctic meteorites, Thur. 5 Dec. / 3F Multipurpose conference room, National Institute of Polar Researc

Noble Gases in the Chelyabinsk Meteorites

The Chelyabinsk meteorite fell in Russia on February 15, 2013 and was classified as LL5 chondrite. The diameter before it entered the atmosphere has been estimated to be about 20 m [1]. Up to now, numerous fragments weighing much greater than 100 kg in total have been collected. In this study, all noble gases were measured for 13 fragments to investigate the exposure history of the Chelyabinsk meteorite and the thermal history of its parent asteroid

Measurements of Shock Effects Recorded by Hayabusa Samples

We requested and have been approved for 5 Hayabusa samples in order definitively establish the degree of shock experienced by the regolith of asteroid Itokawa, and to devise a bridge between shock determinations by standard light optical petrography, crystal structures as determined by synchrotron X-ray diffraction (SXRD), and degree of crystallinity as determined by electron back-scattered diffraction (EBSD) [1,2]. As of the writing of this abstract we are awaiting the approved samples. We propose measurements of astromaterial crystal structures and regolith processes. The proposed research work will improve our understanding of how small, primitive solar system bodies formed and evolved, and improve understanding of the processes that determine the history and future of habitability of environments on other solar system bodies. The results of the proposed research will directly enrich the ongoing asteroid and comet exploration missions by NASA, JAXA and ESA, and broaden our understanding of the origin and evolution of small bodies in the early solar system, and elucidate the nature of asteroid and comet regolith

Crystallographic Characterization of Extraterrestrial Materials by Energy-Scanning X-ray Diffraction

We have continued our long-term project using X-ray diffraction to characterize a wide range of extraterrestrial samples. The stationary sample method with polychromatic X-rays is advantageous because the irradiated area of the sample is always same and fixed, meaning that all diffraction spots occur from the same area of the sample, however, unit cell parameters cannot be directly obtained by this method though they are very important for identification of mineral and for determination of crystal structures. In order to obtain the cell parameters even in the case of the sample stationary method, we apply energy scanning of a micro-beam of monochromatic SR at SPring-8

Mineralogy and crystallography of some Itokawa particles returned by the Hayabusa asteroidal sample return mission

We studied seven Itokawa particles provided by the Japan Aerospace Exploration Agency (JAXA) as first International Announcement of Opportunity (AO) study mainly using electron and synchrotron radiation X-ray beam techniques. All the analyzed particles were collected from the first-touchdown site and composed of olivine and plagioclase with traces of Ca phosphate and chromite, and do not contain pyroxenes. Optical microscopy of these particles shows minor undulatory extinction of olivine and plagioclase, suggesting minor shock metamorphism (shock stage: S2). The electron microprobe analysis shows that olivine is Fo(70-73) and plagioclase is An(13-10)Or(5-7). The synchrotron radiation X-ray diffraction (SR-XRD) analysis of olivine crystals gives cell dimensions of a = 4.708 to 4.779 angstrom, b = 10.271 to 10.289 angstrom, c = 6.017 to 6.024 angstrom, corresponding to the Fo content of Fo(similar to 70) by Vegard's law. This composition matches the result obtained by the electron microprobe analysis. The olivine compositions of the analyzed particles are consistent with those of LL chondrites. The cell dimensions of two plagioclase crystals (a = 8.180 to 8.194 angstrom, b = 12.53 to 12.893 angstrom, c = 7.125 to 7.23 angstrom, a = 92.6 degrees to 93.00 degrees, beta = 116.36 degrees to 116.75 degrees, gamma = 90.03 degrees to 90.17 degrees) indicate that their equilibration temperatures are 800 degrees C +/- 10 degrees C. This temperature is near the peak metamorphic temperature recorded by equilibrated ordinary chondrites. The size of plagioclase crystals and the homogeneity of olivine compositions indicate that their petrologic type is >= 5. We also analyzed plagioclase by SR iron X-ray absorption near-edge structure (SR-XANES) and found that its Fe3+/(Fe2+ + Fe3+) ratio is approximately 0.5. Such high Fe3+ abundance indicates the formation under a relatively oxidizing environment. Thus, all these analyses have reconfirmed that the Itokawa particles returned by the Hayabusa spacecraft are very weakly shocked equilibrated LL chondrites, which matches the results of the preliminary examination team

Adult Intussusception Caused by an Inverted Meckel Diverticulum

Adult intussusception caused by an inverted Meckel diverticulum is rare. We report a 55-year-old Japanese man with intussusception. He was admitted to our hospital with vomiting and abdominal pain. The abdomen was hard with tenderness and muscle guarding. Computed tomography scanning demonstrated a typical inhomogeneous target-shaped mass in the right abdomen. We diagnosed intussusception and performed emergency surgery. At laparotomy, ileocolic intussusception was observed and the ileocecal segment was resected. The surgical specimen comprised an 84 cm segment of resected ileocecum with an elongated polypoid lesion measuring 11 × 2 cm within the ileal lumen. Histopathological examination demonstrated that the polypoid lesion was an inverted Meckel diverticulum. Postoperatively, the patient made an uneventful recovery