[U-06_28PM1] 太陽系小天体研究の新展開

[U06-17] はやぶさカテゴリ３有機物試料中の水素、炭素と窒素同位体組成

*伊藤 元雄¹、上椙 真之²、奈良岡 浩³、薮田 ひかる⁴、北島 富美雄³、三田 肇⁵、高野 淑識⁶、唐牛 譲²、矢田 達²、石橋 之宏²、岡田 達明²、安部 正真² (1.海洋研究開発機構　高知コア研究所、2.宇宙航空研究開発機構、3.九州大学大学院理学研究院地球惑星科学部門、4.大阪大学大学院理学研究科宇宙地球科学専攻、5.福岡工業大学工学部生命環境科学科、6.海洋研究開発機構　海洋・極限環境生物圏領域)

Hayabusa spacecraft had brought back asteroid Itokawa particles to the Earth on June 2010. More than 1,500 mineral particles were identified on the Qz glass after the compulsive free fall, and most of them were very small ranging from 10 to 300 μm but are mostly smaller than 50 μm (Nakamura et al., 2011). In addition several amount of carbonaceous materials were found that is called Category 3. Based on FE-SEM and EDS observations at JAXA Extraterrestrial Sample Curation Team, those samples mainly composed of C, N, O and some of them contain NaCl and KCl (JAXA Hayabusa sample catalogue).H, C and N isotopic compositions of extraterrestrial organic materials in Stardust cometary samples (McKeegan et al., 2006), IDPs (Messenger, 2000), IOM (Busemann et al. 2006) and nanoglobules in primitive chondrite (Nakamura-Messenger et al., 2006) provide a clue for understanding of origin and nature of the Solar System. Large D and 15N isotopic enrichments were observed, and C isotope is slightly enriched in 13C in extraterrestrial organic materials (Pizzarello, 2005). Those data suggest that extraterrestrial organics are probably interstellar material that was survived through formation processes (planetesimals) of the Solar System (Sanford et al., 2001), and may also have material that formed in the cold molecular cloud region of the protoplanetary disk (Aikawa et al., 2002).Here we report H, C and N isotopic measurement of organic materials from Hayabusa Category 3 samples, RB-QD04-0047-02, RA-QD02-0120 and RB-QD04-0001, by an ion imaging with the JAMSTEC NanoSIMS ion microprobe. The purposes of this study are to evaluate terrestrial contaminations in the Hayabusa spacecraft and in the JAXA curation facility, and to find extraterrestrial organic materials on the basis of H, C and N isotope measurements.Each Hayabusa organic sample was pressed on Au plate together with terrestrial organic standards of 1-hydroxybenzotriazole hydrate and BBOT with known H, C and N isotopic compositions. Following the SEM study to check the sample condition, texture and morphology, the samples were analyzed for H, C and N isotopic compositions by an isotopic imaging with the JAMSTEC NanoSIMS 50L at Kochi Institute for Core Sample Research.We studied three Hayabusa organic samples, RB-QD04-0047-02, RA-QD02-0120 and RB-QD04-0001. All of the samples have been initially investigated by a FE-SEM and EDX observation at JAXA Hayabusa curation facility, and the EDX spectra of the samples contain C, N and O; the dominant elements are C, and N (Hayabusa sample catalogue). Based on NanoSIMS isotopic images of H, C and N in RB-QD04-0047-02, RA-QD02-0120 and RB-QD04-0001, all three samples show homogeneous and terrestrial H, C and N isotopic compositions within an error (δD = 60 ± 13 permil, δ13C = 3 ± 3 permil and δ15N = -4 ± 2 permil for RB-QD04-0047-02; δD = 81 ± 54 permil, δ13C = -20 ± 8 permil and δ15N = 2 ± 2 permil for RA-QD02-0120; δD = 135 ± 32 permil, δ13C = -20 ± 9 permil and δ15N = 16 ± 12 permil for RB-QD04-0001).The IOMs in CI and CM chondrites show heterogeneous distributions of delta-D at the molecular (Remusat et al. 2009) and micron scale level (Busemann et al., 2006). The IOMs of CR, CM and CI have D and 15N isotopic enrichments in micron-sized regions (hot spots). The IOMs in ordinary chondrites are heterogeneous, however, they do not show many micron-scale anomalies as IOMs in carbonaceous chondrite (Remusat et al., 2013). It is obvious that H, C and N isotope signatures of Hayabusa organic samples are different from those of IOMs in carbonaceous and ordinary chondrites: i.e., No hot spots, terrestrial values for H, C and N isotopes.We have not found strong evidence of extraterrestrial origin because isotope compositions of H, C and N in Hayabusa organic samples show terrestrial values, and homogen