スターダスト探査機により回収された短周期彗星81P/ビルド2のコンドリュール

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Many small rock particles have been successfully recovered from a short-period comet 81P/Wild 2 by the Stardust mission. They are believed to be very primitive dust at outer regions of the protoplanetary disk, because short-period comets originally formed as Kuiper-belt objects that currently locate at 30-50 AU from the Sun. Chondrules are sub-millimeter to millimeter size objects formed in the inner protoplanetary disk by total or partial melting of silicate-rich dust particles. They are a major constituent of chondrites from asteroids. Among the particles from the comet Wild 2, we found pieces of chondrules that show igneous texture and have mineral compositions and major and most minor element concentrations very similar to chondrules in primitive meteorites derived from asteroids. Oxygen isotope ratios are highly heterogeneous from - 50 to + 5‰ in δ^<18>O_<SMOW> and plotted nearly along the slope = 1 mass independent fractionation line in the oxygen three isotope diagram, which characterizes chondrules in carbonaceous chondrites that comprise middle to outer asteroid belt. These observations suggest that the particles are pieces of chondrules formed through the least degree of melting, crystallization, and elemental and isotopic equilibration at high temperatures. The presence of chondrules in a short-period comet from the Kuiper belt indicates that chondrules migrated from hot inner regions to cold outer regions of the disk and spread widely over the early solar nebula.
日本地球化学会の論文

スターダスト探査機により回収された短周期彗星81P/ビルド2のコンドリュール

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