The Distribution and Inventory of Stardust Grains in Primitive Solar System Materials: Implications from Isotopic, Elemental and Petrologic Studies of Meteorites and Cometary Dust

原始陨石、行星际尘埃和彗星物质中含有少量所谓的前太阳或星尘颗粒。这些矿物颗粒形成于演化恒星的风中或新星和超新星爆炸的喷出物中，比我们的太阳系更古老，随后被纳入大约46亿年前形成我们太阳系的分子云中。前太阳颗粒可以通过其相对于太阳系平均物质的高度异常同位素组成来与太阳系中形成的固体区分开来。它们的浓度在不同的原始太阳系物质中有所不同，显然反映了母体的变质过程，也可能反映了太阳星云的不均匀性。在这里，我将调查前太阳晶粒库存不同水库的细粒材料（细粒尘埃轮辋和球粒间矩阵）在CR和CM陨石，这是最原始的陨石，通过NanoSIMS离子成像。这些陨石的细粒部分的岩石学和元素组成将通过扫描电子显微镜（SEM），基于SEM的能量色散X射线光谱（SEM-EDS）和电子探针进行详细研究，并与各自的太阳前颗粒库存进行比较。这使得调查的热和水的蚀变和形成的CR和CM陨石的场景的影响，并确定在太阳星云内的CR和CM陨石的形成区域的太阳前颗粒丰度的约束。我还将对来自NASA星尘使命返回的彗星81 P/Wild 2的材料进行研究，以探索目前尚未很好确定的来自这个原始太阳系天体的物质中的太阳前颗粒丰度。彗星尘埃的撞击坑将通过扫描电子显微镜在STARDUST彗星尘埃收集器的铝箔中进行识别。剩余物质将通过SEM-EDS表征，并且将通过NanoSIMS离子成像分析前太阳能颗粒库存。

Primitive meteorites, interplanetary dust and cometary material contain small concentrations of so-called presolar or stardust grains. These mineral grains, which formed in the winds of evolved stars or in the ejecta of nova and supernova explosions, are older than our Solar System and were subsequently incorporated into the molecular cloud from which our Solar System formed some 4.6 billion years ago. Presolar grains can be distinguished from solids that formed in the Solar System by their highly anomalous isotopic compositions with respect to average Solar System material. Their concentrations vary among different primitive Solar System materials, apparently reflecting metamorphic processes on the parent bodies and possibly also heterogeneities in the solar nebula. Here, I will investigate the presolar grain inventories different reservoirs of fine-grained material (fine-grained dust rims and interchondrule matrix) in CR and CM chondrites, which are amongst the most primitive meteorites, by NanoSIMS ion imaging. The petrology and elemental composition of the fine-grained portions of these meteorites will be studied in detail by scanning electron microscopy (SEM), SEM-based energy-dispersive x-ray spectroscopy (SEM-EDS), and electron microprobe and compared with the respective presolar grain inventories. This allows to investigate the effects of thermal and aqueous alteration and formation scenarios for CR and CM chondrites, and to determine constraints on the presolar grain abundance in formation regions of the CR and CM chondrites within the solar nebula. I will also conduct a study of material from comet 81P/Wild 2, returned by NASAs STARDUST mission, in order to explore the currently still not well determined presolar grain abundance in matter from this pristine Solar System body. Impact craters of cometary dust will be identified in Al foils from the STARDUST cometary dust collector by SEM. The residual matter will be characterized by SEM-EDS, and the presolar grain inventory will be analyzed by NanoSIMS ion imaging.