日本地球惑星科学連合2015年大会

講演情報

ポスター発表

セッション記号 P (宇宙惑星科学) » P-PS 惑星科学

[P-PS22] 太陽系における惑星物質の形成と進化

2015年5月27日(水) 18:15 〜 19:30 コンベンションホール (2F)

コンビーナ:*伊藤 正一(京都大学大学院理学研究科)、臼井 寛裕(東京工業大学地球惑星科学科)、瀬戸 雄介(神戸大学大学院理学研究科)、宮原 正明(広島大学理学研究科地球惑星システム学専攻)、木村 眞(茨城大学理学部)、大谷 栄治(東北大学大学院理学研究科地学専攻)、三浦 均(名古屋市立大学大学院システム自然科学研究科)、薮田 ひかる(大阪大学大学院理学研究科宇宙地球科学専攻)

18:15 〜 19:30

[PPS22-P08] 浮遊法による放射状輝石コンドリュールの組織再現実験

*野村 逸郎1中村 智樹1木村 勇気2塚本 勝男3三浦 均4上椙 真之5上杉 健太朗6星野 真人6 (1.東北大学大学院理学研究科、2.北海道大学低温科学研究所、3.大阪大学大学院工学研究科、4.名古屋市立大学大学院システム自然科学研究科、5.宇宙航空研究開発機構、6.高輝度光科学研究センター)

Chondrules, igneous silicate spherules, formed by transient heating and rapid cooling, are ubiquitously contained in primitive chondrites. But, the formation conditions of chondrules in the protoplanetary disks are still unclear. In order to constrain the formation conditions of chondrules, a number of reproduction experiments in a electric furnace have been performed (e.g., Tsuchiyama et al., 1980). In these experiments, a melt droplet sample was hung on a platinum wire and thus the melt did contact with a platinum loop wire, possibly leading to heterogeneous nuclation near equiribrium temperatures. While, Tsukamoto et al. (2000) started a non-contact method, namely acoustic levitation method and microgravity levitation for the first time for chondrule synthesis, followd by Nagashima et al. (2006) who employed a gas jet levitation method. In both cases, space envieronment was simulated because crystallization of a melting silicate sphere occurs in a levitated condition.
In this study, we performed experiments to reproduce the textures of radial pyroxene chondrules using the gas jet levitation furnace used in Nagashima et al. (2006). Samples are 1-2mm spheres and chemical compositions of the samples are similar as of the natural radial pyroxene chondrules excluding iron. The sample was completely melted at about 1600-1800 ℃with a 100W CO2 laser and cooling rate after heating was about 104-106K / hr. We used an argon gas in order to levitate samples. After the experiment, the samples were analyzed by optical microscope and scanning electron microscope. Three dimensional images of the internal texture were also obtained after crystallization using X-ray computed tomography at at SPring-8 (BL20B2).
The textures similar to natural radial pyroxene chondrules were reproduced at the cooling rates of about 104K/hr. At faster cooling rates (105-106K/hr), samples became transparent glass without any crystals. These glass chondrules rarely exist in nature. The cooling rates (~104K/hr) that successfully reproduced chondrules are slower than the calculated cooling rate (106K/hr) of the melt whose temperature decreases by radiation alone in vacuum. When the nucleation center of the radial texture was observed by high magnification optical microscopy, there in most cases exists a tiny particle that is different from the radial pyroxene. This implies the importance of the heterogeneous nucleation from the tiny particles, which might be formed prior to the formation of the radial texture or impurities simply coming from dusts or the chemical reagent. These experimental data would lead to a discussion on the chondrule formation in the protoplanetary disk in the presence of gases that slowed down the cooling.