PERSPECTIVES OF SOLAR SYSTEM EVOLUTION BY
COMPARISONS OF ASTEROIDAL MATERIALS AND
MINERALOGY OF SOME EVOLVED METEORITES.
H. Takeda1, H. Nagaoka2, A. Yamaguchi3, Y. Karouji4 and Y.
Yazawa5. 1Univ. of Tokyo, Graduate School of Sci. & Chiba Inst.
of Tech., Forum Res. E-mail: takeda.hiroshi@it-chiba.ac.jp.
2
Waseda Univ., Res. Inst. for Sci. & Engn., 3Natnl. Inst. of PolarRes., 4JAXA/ISAS, 5Chiba Inst. of Tech.(CIT), Dept. of Life &Environm. Sci.
Introduction: Because of the recent investigations on the returned dusts from the Itokawa by the Hayabusa Mission [1], wehave a renewed interest in the LL chondrite parent body, in order
to better understand the evolutional processes on an asteroidalbody. It is generally understood that the chondritic materials preserve the chemical records of primitive solar system materials,
because their parent bodies are mostly small. This statement is
not supported if we recognize the presence of a Vest-like asteroid
larger than 500 km in diameter [2]. We will compare the degreeof differentiation of the Vesta-like body with those of the LL
chondrite parent body. We already pointed out that zoning profiles of pyroxenes in totally molten LL chondrites including Y790964 [3] are comparable with one grain in the Itokawa dusts[1]. In this paper, we will report other partly molten LL chondrites, to discuss evolution of the LL body with respect to Vesta.
Samples and Methods: We reexamined two PTSs (polishedthin sections) of LL chondrites Y-981971,51-1, Y-793214,92-1(LL5), and a new PTS Y-790782,91-2 prepared at the NIPR wasobserved by a petrographic microscope and EPMA.
Y981971,51-1 and Y-790782,91-2 were analyzed with a JEOL
JXA-8900 EPMA at AORI (Atomosph. Ocean Res. Inst.).
Results: We found the first evidence of a product of partial
melting of the chondritic primitive solar system materials withalbite and diopside assemblage in Y-74160 [4] and similar materials were recognized in other LL with granulitic texture. Y790782,91-2 (0.9X0.8 mm in size) consists of dark fine-grained
mafic silicates with opaque spherules up to 7 mm in diameter
distributed throughout the PTS. There is no metallic vein in thisPTS, but the spherules (Fe,Ni,S) indicate melting.
Discussion: In-situ observation and sample return from asteroid Itokawa by Hayabusa Mission, are revealing data whichcannot be obtained either from ground-based observations or meteorite studies to unravel the origin of the solar system. However,the presence of the product of a partial melt in a chondrite parent
body suggests that even the primitive solar system material, suchas chondrites experienced strong thermal events.
Products of high temperature episodes. The mineralogy ofVesta, based on data obtained by the Dawn mission [5], is consistent with HED achondrites, and confirmed the presence of theproposed layered crust model [3]. This largest asteroid is thelargest protoplanet visited to date, and thereby provides a direct
link to materials of the smallest terrestrial planet and basic modeof planetary evolution of the solar system.
References: [1] Nakamura T. et al. 2011. Science, 333,1113-1116. [2] Takeda H. 1997. Meteoritics & Planetary Science32, 841-853. [3] Miyamoto M., Takeda H. and Ishii T. 1984.
Journal of Geophysical Research 89:11581–11588. [4] Takeda
H., Huston T. J. and Lipschutz M. E. 1984. Earth & Planetary
Science Letter 71, 329-339. [5] De Sanctis M. C. et al. 2012.
Science 336, 697-700.