Japan Geoscience Union Meeting 2016

Presentation information


Symbol P (Space and Planetary Sciences) » P-PS Planetary Sciences

[P-PS12] Formation and evolution of planetary materials in the solar system

Tue. May 24, 2016 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL6)

Convener:*Masaaki Miyahara(Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University), Akira Yamaguchi(National Institute of Polar Research), Tomohiro Usui(Department of Earth and Planetary Sciences,Tokyo Institute of Technology), Yoko Kebukawa(Faculty of Engineering, Yokohama National University), Wataru Fujiya(Ibaraki University, College of Science), Yusuke Seto(Graduate School of Science, Kobe University), Shoichi Itoh(Graduate school of Science, Kyoto University)

5:15 PM - 6:30 PM

[PPS12-P05] Be-B systematics of refractory inclusions in CO and CH chondrites

*Kohei Fukuda1, Wataru Fujiya2, Hajime Hiyagon1, Naoji Sugiura1, Naoto Takahata3, Yuji Sano3 (1.Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, 2.College of Science, Ibaraki University, 3.Atmosphere and Ocean Research Institute (AORI), University of Tokyo)

Keywords:early solar system, irradiation processes, Be-B isotopes

Observations of solar-type Young Stellar Objects (YSOs) have shown enhanced and frequent X-ray flares accompanied by intense flux of accelerated particles [1]. The powerful X-ray activity around newborn stars suggests that intense irradiation from the proto-Sun has also occurred in the early solar nebula. Be-B systematics of refractory inclusions, the first solids in our solar system [2, 3], can potentially shed light on irradiation processes in the early solar system.
Previous studies have demonstrated that a short-lived radionuclide 10Be, which decays to 10B with a half-life of 1.4Myr [4], was present in the early solar system with initial 10Be/9Be ratios ranging from 10-4 to 10-2 [5-13]. However, most of the data come from refractory inclusions in CV3 chondrites. To further investigate the distribution of 10Be and irradiation conditions in the early solar system, we conducted Be-B isotopic measurements using a NanoSIMS 50 (at AORI, Univ. of Tokyo) on compact melilite-rich CAIs in primitive chondrites, Y81020 (C03.05) and SaU290 (CH3).
The melilite-rich CAI in Y81020 yields an isochron with the initial 10Be/9Be ratio comparable to those of CV CAIs within uncertainties. The results suggest that CO CAIs have also experienced irradiation processes similar to CV CAIs. In contrast, a melilite-rich CAI in SaU290 shows no resolvable excesses in 10B from the terrestrial value. Previous studies have demonstrated that hibonite-rich inclusions in CMs and FUN inclusions in CVs typically show lower 10Be/9Be ratios than those of most normal CAIs [7, 9, 12, 13]. In addition, these inclusions are known to have low 26Al abundances, which is interpreted as their formation prior to the injection of 26Al into the solar system [e.g., 14]. These observations may suggest that FUN-like inclusions record irradiation history in the protosolar molecular cloud [9, 15] and/or heterogeneous distribution of 10Be in the early solar system [12, 13]. A substantial fraction of CH CAIs also has little 26Al [16], suggesting possible relevance to FUN-like inclusions. The low 10Be/9Be ratio of the CH CAI observed in this study could, therefore, support the above hypothesis.
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