Mineralogy and petrology of Stardust particles encased in the bulb of track 80: TEM investigation of the Wild 2 fine-grained material
Mineralogy and petrology of Stardust particles encased in the bulb of track 80: TEM investigation of the Wild 2 fine-grained material
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轨道 80 球体中星尘颗粒的矿物学和岩石学：Wild 2 细粒材料的 TEM 研究
DOI：
10.1016/j.gca.2012.03.026
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发表时间：
2012
影响因子：
5
通讯作者：
H. Leroux
中科院分区：
文献类型：
--
作者：
J. Stodolna;D. Jacob;H. Leroux
我们用透射电子显微镜分析了从星尘轨道80的壁上提取的样品的矿物学特征。利用常规成像、电子衍射和EDX微量分析对500多个碎片进行了研究。两类粒子以相同的比例（wt%）可区分。第一类由较大晶粒（平均≈1μm）组成，主要为硅酸盐（橄榄石和辉石）；它们显示出与终端粒子相媲美的广泛的成分和微观结构。小相包括磁铁矿和磷灰石也存在。它们的出现表明Wild 2号物质在一定程度上经历了水蚀作用。第二种类型的粒子被称为类宝石材料，由富含二氧化硅的玻璃团块组成，内含硫化铁珠和小泡。它们的微观结构是在超高速撞击过程中与二氧化硅气凝胶发生强烈相互作用的热改性颗粒的特征。这些熔化的物质可能是由熔化和蒸发的物质脱落而形成的，但考虑到撞击轨迹的形状和幸存的矿物成分的高度多样性，其中大部分来自收集过程中分解的细粒聚集体。纳米尺度上的化学作图可以在富含硅的玻璃中定位单个成分。它们以尺寸小于300nm的富镁元件为主。这种经过热修饰的物质的平均组成接近于主要元素Fe、Mg和s的太阳丰度。细粒物质在与Wild 2彗星结合之前可能没有在原行星盘中进行化学分异，不像球粒陨石的硫耗尽基质。从这两类颗粒中，我们推断Wild 2可能是由相对较大的进化颗粒（第一类）的组合组成的，这些颗粒由具有原始化学性质的细颗粒材料（第二类）粘合而成。从这项研究中推断出的入射物质的撞击前结构似乎与最原始的球粒陨石（3.0）的基质或球粒状多孔行星际尘埃颗粒相当。
We have characterized by transmission electron microscopy the mineralogy of samples extracted from the walls of the Stardust track 80. More than 500 fragments were studied using conventional imaging, electron diffraction and EDX microanalysis. Two categories of particles are distinguishable in equal proportions (wt%). The first one is comprised of relatively large crystalline grains (≈1μm on average), dominated by silicates (olivine and pyroxene). They display a wide range of compositions and microstructures comparable to those found in terminal particles. Minor phases including magnetite and apatite are also present. Their occurrence suggests that the Wild 2 material underwent aqueous alteration to some extent. The second type of particle, called GEMS-like material, is made of silica-rich glassy clumps embedding iron sulfide beads and vesicles. Their microstructure is characteristic of thermally modified particles that have suffered strong interaction with the silica aerogel during the hypervelocity impact. This melted material may form by shedding of melted and vaporized material, but given the shape of the impact track and high diversity of surviving mineral compositions, much of it originated from fine-grained aggregates that disaggregated during the collection. Chemical mapping at the nano-scale allowed the localization of individual components within the silica-rich glass. They are dominated by Mg-rich components with a size less than 300nm. The average composition of this thermally modified material is close to the solar abundance for the major elements Fe, Mg and S. The fine-grained material has probably not been chemically fractionated in the protoplanetary disk before its incorporation in comet Wild 2 unlike the sulfur depleted matrix of chondrites. From these two categories of particles, we deduce that Wild 2 is likely made of an assemblage of relatively large evolved grains (first category) cemented by a fine-grained material with primitive chemistry (second category). The pre-impact configuration of the incident material deduced from this study seems comparable to the matrix of the most primitive chondrites (3.0) or to chondritic porous interplanetary dust particles.
彗星 81P/Wild 2 中的铁氧化物
影响因子：
2.2
作者：
BRIDGES J
通讯作者：
BRIDGES J