The Inventory of Stardust Grains in the Solar Nebula - Implications from Isotopic and Petrologic Studies of Primitive Solar System Materials

原始陨石、行星际尘埃颗粒和来自彗星81 P/Wild 2的样本都含有少量的耐火尘埃颗粒，这些尘埃颗粒比我们的太阳系还要古老，形成于演化恒星的风中或恒星爆炸的喷出物中。这些前太阳（星尘）颗粒可以根据相对于平均太阳系物质的大量同位素异常来识别。它们的丰度在不同的原始太阳系物质中各不相同，显然反映了次级蚀变过程（例如，水蚀变或热加热），也可能是太阳星云的不均匀性。在这里，我们将继续调查CR族陨石的太阳前颗粒库存，这是已知的最原始的陨石之一，通过NanoSIMS离子成像。这些陨石的基质岩石学将通过光学显微镜和电子探针进行详细研究，并与太阳前颗粒清单进行比较，以调查热蚀变和水蚀变的影响，CR族陨石的成因关系和形成情景，并推断太阳星云中太阳前颗粒丰度的限制。我们还将继续研究由美国宇航局的星尘使命返回的怀尔德2号彗星的物质，以探索目前尚未确定的太阳系原始天体物质中的太阳前颗粒丰度。这些研究将辅之以对STARDUST星际尘埃收集器铝箔撞击坑中残留物的搜索和可能的化学和同位素研究。

Primitive meteorites, interplanetary dust particles, and samples from comet 81P/Wild 2 contain small quantities of refractory dust grains that are older than our Solar System and which formed in the winds of evolved stars or in the ejecta of stellar explosions. These presolar (stardust) grains can be identified on the basis of large isotopic anomalies with respect to average Solar System matter. Their abundances vary among different primitive Solar System materials, apparently reflecting processes of secondary alteration (e.g., aqueous alteration or thermal heating) and possibly also heterogeneities in the solar nebula. Here, we will continue to investigate the presolar grain inventories of CR clan chondrites, which are amongst the most primitive meteorites known, by NanoSIMS ion imaging. The matrix petrology in these meteorites will be studied in detail by optical microscopy and electron microprobe and compared with the presolar grain inventory to investigate the effects of thermal and aqueous alteration, genetic relationships and formation scenarios for CR clan chondrites, and to infer constraints on the presolar grain abundance in the solar nebula. We will also continue to study matter from comet Wild 2, returned by NASA’s STARDUST mission, in order to explore the currently not well determined presolar grain abundance in matter from this pristine Solar System body. These studies will be complemented by a search for and possible chemical and isotopic studies of residues in impact craters in Al foils from STARDUST’s interstellar dust collector.