Isotopic anomalies in organic nanoglobules from Comet 81P/Wild 2: Comparison to Murchison nanoglobules and isotopic anomalies induced in terrestrial organics by electron irradiation
Isotopic anomalies in organic nanoglobules from Comet 81P/Wild 2: Comparison to Murchison nanoglobules and isotopic anomalies induced in terrestrial organics by electron irradiation
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DOI：
10.1016/j.gca.2010.05.010
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发表时间：
2010-08-01
影响因子：
5
通讯作者：
Zega, Thomas J.
中科院分区：
文献类型：
--
作者：
De Gregorio, Bradley T.;Stroud, Rhonda M.;Zega, Thomas J.
纳米微粒是一种存在于行星际尘埃颗粒和原始陨石中的有机物质，通常与暗示星际过程的N-15和D同位素异常有关。我们报告发现的两个同位素异常的有机小球从星尘收集的颗粒从彗星81 P/野生2和比较他们与纳米微粒从默奇森CM 2陨石。来自星尘号彗星轨道80的一个球状体含有高度芳香的有机物质和一个大的N-15异常（Δ N-15 = 1120千分之一）。来自这条轨道的相关的非球状有机物质在N-15中的富集程度较低，并且含有芳香族和氧化碳的混合物，类似于原始陨石中的大量不溶性有机物质（IOM）。第二个小球，来自彗星轨道2，含有非芳香族有机物质，具有丰富的腈（-C N）和羧基（-COOH）官能团。它的D含量非常丰富（D =千分之1000），但具有陆地N-15/N-14比率。实验表明，类似的D富集，不伴随N-15分馏，可以在实验室中通过环氧树脂或氰基丙烯酸酯的电子辐照再现。因此，不能排除这种球状体的陆地起源，相反，在太空中暴露于高能电子辐照可能是产生有机材料D异常的一个重要因素。为了比较，我们报告两个默奇森球：一个具有大的N-15富集和高度芳香族化学类似的轨道80球和其他只有适度富集N-15与IOM样化学。对81 P/Wild 2彗星中有机小球的观察表明，彗星可能采样了与球粒陨石母体相同的有机物质储存库。在球状体中观察到的同位素异常很可能是低温（
Nanoglobules are a form of organic matter found in interplanetary dust particles and primitive meteorites and are commonly associated with N-15 and D isotopic anomalies that are suggestive of interstellar processes. We report the discovery of two isotopically-anomalous organic globules from the Stardust collection of particles from Comet 81P/Wild 2 and compare them with nanoglobules from the Murchison CM2 meteorite. One globule from Stardust Cometary Track 80 contains highly aromatic organic matter and a large N-15 anomaly (delta N-15 = 1120 parts per thousand). Associated, non-globular, organic matter from this track is less enriched in N-15 and contains a mixture of aromatic and oxidized carbon similar to bulk insoluble organic material (IOM) from primitive meteorites. The second globule, from Cometary Track 2, contains non-aromatic organic matter with abundant nitrile (-C N) and carboxyl (-COOH) functional groups. It is significantly enriched in D (delta D = 1000 parts per thousand) but has a terrestrial N-15/N-14 ratio. Experiments indicate that similar D enrichments, unaccompanied by N-15 fractionation, can be reproduced in the laboratory by electron irradiation of epoxy or cyanoacrylate. Thus, a terrestrial origin for this globule cannot be ruled out, and, conversely, exposure to high-energy electron irradiation in space may be an important factor in producing D anomalies in organic materials. For comparison, we report two Murchison globules: one with a large N-15 enrichment and highly aromatic chemistry analogous to the Track 80 globule and the other only moderately enriched in N-15 with IOM-like chemistry. The observation of organic globules in Comet 81P/Wild 2 indicates that comets likely sampled the same reservoirs of organic matter as did the chondrite parent bodies. The observed isotopic anomalies in the globules are most likely preserved signatures of low temperature (