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系或星尘颗粒。这些矿物颗粒是在演化恒星的气流中形成的，或者是在新星和超新星爆炸的喷出物中形成的，它们比我们的太阳系更古老，随后被合并到分子云中，大约46亿年前，我们的太阳系就是从分子云中形成的。太阳系前颗粒可以与太阳系中形成的固体区分开来，因为它们的同位素组成相对于太阳系的平均物质来说非常异常。它们的浓度在不同的原始太阳系物质中有所不同，这显然反映了母体的变质过程，也可能反映了太阳星云中的异质性。在这里，我将通过纳米sims离子成像研究CR和CM球粒陨石中不同细粒物质（细粒尘埃边缘和球粒间基质）的太阳前颗粒清单，这是最原始的陨石之一。通过扫描电子显微镜（SEM）、基于SEM的能量色散x射线能谱（SEM- eds）和电子探针对这些陨石细粒部分的岩石学和元素组成进行了详细研究，并与各自的太阳前颗粒清单进行了比较。这使得研究热蚀和含水蚀变对CR和CM球粒陨石的影响和形成情景，并确定太阳星云中CR和CM球粒陨石形成区域的太阳前颗粒丰度的限制。我还将对美国宇航局“星尘”任务返回的81P/Wild 2号彗星的物质进行研究，以探索这个原始太阳系天体中目前尚未确定的太阳系前物质的颗粒丰度。彗星尘埃的撞击坑将通过扫描电镜在星尘彗星尘埃收集器的铝箔中识别出来。利用SEM-EDS对残余物质进行表征，利用NanoSIMS离子成像对太阳前颗粒进行分析。

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.