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arXiv 1506.04783astro-ph.EP
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81 P/Wild 2彗星粗、细粒物质的氧同位素组成

Oxygen Isotopic Composition of Coarse- and Fine-grained Material from Comet 81P/Wild 2

Ryan C. Ogliore, Kazuhide Nagashima, Gary R. Huss, Andrew J. Westphal, Zack Gainsforth, Anna L. Butterworth

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摘要：

由美国宇航局星尘任务收集的81 P/Wild 2彗星的单个颗粒大小不一，从气凝胶轨道壁上发现的小于$μ$ m的小碎片到轨道末端发现的高达数十个$μ$ m的大碎片。这颗彗星自形成以来就在海王星以外的轨道上运行，保留了完整的早期太阳系过程记录，这些记录在小行星样本中受到加热和水蚀变的影响。我们测量了从五个不同的星尘气凝胶轨道中提取的大于$\sim$ 2 $μ$ m的七个星尘碎片的O同位素组成，以及从星尘轨道壁中提取的小于$\sim$ 2 $μ$ m的63个颗粒。较大的颗粒显示出相对较窄的O同位素组成范围，这与陨石中常见的$^{16}$ O-贫相一致。迄今为止研究的许多较大的星尘碎片都具有类似球粒的矿物学特征，这与内太阳系的形成相一致。细粒材料显示出非常广泛的O同位素组成（$-70<Δ^{17}$ O $<+60$），这表明怀尔德2号细粒要么是原始的外星云尘埃，要么是内太阳系成分储层的非常多样化的样本，这些储层与大量的内太阳系岩石一起增生形成了彗星怀尔德2号。

英文摘要：

Individual particles from comet 81P/Wild 2 collected by NASA's Stardust mission vary in size from small sub-$μ$m fragments found in the walls of the aerogel tracks, to large fragments up to tens of $μ$m in size found towards the termini of tracks. The comet, in an orbit beyond Neptune since its formation, retains an intact a record of early-Solar-System processes that was compromised in asteroidal samples by heating and aqueous alteration. We measured the O isotopic composition of seven Stardust fragments larger than $\sim$2 $μ$m extracted from five different Stardust aerogel tracks, and 63 particles smaller than $\sim$2 $μ$m from the wall of a Stardust track. The larger particles show a relatively narrow range of O isotopic compositions that is consistent with $^{16}$O-poor phases commonly seen in meteorites. Many of the larger Stardust fragments studied so far have chondrule-like mineralogy which is consistent with formation in the inner Solar System. The fine-grained material shows a very broad range of O isotopic compositions ($-70<Δ^{17}$O$<+60$) suggesting that Wild 2 fines are either primitive outer-nebula dust or a very diverse sampling of inner Solar System compositional reservoirs that accreted along with a large number of inner-Solar-System rocks to form comet Wild 2.

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