Larry R Nittler , Jens Barosch , Katherine Burgess , Rhonda M Stroud , Jianhua Wang , Hikaru Yabuta , Yuma Enokido , Megumi Matsumoto , Tomoki Nakamura , Yoko Kebukawa , Shohei Yamashita , Yoshio Takahashi , Laure Bejach , Lydie Bonal , George D Cody , Emmanuel Dartois , Alexandre Dazzi , Bradley De Gregorio , Ariane Deniset-Besseau , Jean Duprat , Yuichi Tsuda
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The isotopic distributions of the Ryugu samples from two different collection spots are closely similar to each other and to the Orgueil samples, strengthening the proposed Ryugu-CI chondrite connection. Most individual sub-μm organic grains have isotopic compositions within error of bulk values, but 2–10 % of them are outliers exhibiting large isotopic enrichments or depletions in D, <sup>15</sup>N, and/or <sup>13</sup>C. The H, C and N isotopic compositions of the outliers are not correlated with each other: while some organic grains are both D- and <sup>15</sup>N-enriched, many are enriched or depleted in one or the other system. This most likely points to a diversity in isotopic fractionation pathways and thus diversity in the local formation environments for the individual outlier grains. The observation of a relatively small population of isotopic outlier grains can be explained either by escape from nebular and/or parent body homogenization of carbonaceous precursor material or addition of later isotopic outlier grains. The strong chemical similarity of isotopically typical and isotopically outlying grains, as reflected by synchrotron x-ray absorption spectra, suggests a genetic connection and thus favors the former, homogenization scenario. 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引用次数: 0
摘要
我们报告了小行星 "龙宫 "和Orgueil CI碳质软玉样本中微米级(0.2至2微米)有机物的H、C和N同位素组成。通过 NanoSIMS 同位素成像分析了隼鸟 2 号航天器返回的小行星龙宫的三个碎屑颗粒和 Orgueil 的几个碎片。来自两个不同采集点的龙宫样本的同位素分布与Orgueil样本十分相似,这加强了龙宫与CI软玉的联系。大多数亚微米有机颗粒的同位素组成与主体值的误差在一定范围内,但其中有2-10%的颗粒是异常值,表现出D、15N和/或13C的大量同位素富集或贫化。异常值中的 H、C 和 N 同位素组成彼此并不相关:虽然有些有机颗粒同时富含 D 和 15N,但许多有机颗粒却只富含或贫乏其中一个系统。这很有可能表明同位素分馏途径的多样性,从而表明各个离群岩粒的局部形成环境的多样性。观测到相对较少的同位素离群晶粒,其原因可能是碳质前体物质摆脱了星云和/或母体的同质化,也可能是后来同位素离群晶粒的加入。同步辐射 X 射线吸收光谱显示,同位素典型晶粒和同位素离群晶粒的化学性质非常相似,这表明两者之间存在遗传联系,因此更倾向于前一种同质化情况。然而,即使是变化最小的陨石也显示出相同的模式,即在较大的同质化颗粒群之上有一小部分离群颗粒,这表明部分或大部分同质化发生在大分子有机颗粒吸积到小行星母体之前。
Microscale hydrogen, carbon, and nitrogen isotopic diversity of organic matter in asteroid Ryugu
We report the H, C, and N isotopic compositions of microscale (0.2 to 2 µm) organic matter in samples of asteroid Ryugu and the Orgueil CI carbonaceous chondrite. Three regolith particles of asteroid Ryugu, returned by the Hayabusa2 spacecraft, and several fragments of Orgueil were analyzed by NanoSIMS isotopic imaging. The isotopic distributions of the Ryugu samples from two different collection spots are closely similar to each other and to the Orgueil samples, strengthening the proposed Ryugu-CI chondrite connection. Most individual sub-μm organic grains have isotopic compositions within error of bulk values, but 2–10 % of them are outliers exhibiting large isotopic enrichments or depletions in D, 15N, and/or 13C. The H, C and N isotopic compositions of the outliers are not correlated with each other: while some organic grains are both D- and 15N-enriched, many are enriched or depleted in one or the other system. This most likely points to a diversity in isotopic fractionation pathways and thus diversity in the local formation environments for the individual outlier grains. The observation of a relatively small population of isotopic outlier grains can be explained either by escape from nebular and/or parent body homogenization of carbonaceous precursor material or addition of later isotopic outlier grains. The strong chemical similarity of isotopically typical and isotopically outlying grains, as reflected by synchrotron x-ray absorption spectra, suggests a genetic connection and thus favors the former, homogenization scenario. However, the fact that even the least altered meteorites show the same pattern of a small population of outliers on top of a larger population of homogenized grains indicates that some or most of the homogenization occurred prior to accretion of the macromolecular organic grains into asteroidal parent bodies.
期刊介绍:
Earth and Planetary Science Letters (EPSL) is a leading journal for researchers across the entire Earth and planetary sciences community. It publishes concise, exciting, high-impact articles ("Letters") of broad interest. Its focus is on physical and chemical processes, the evolution and general properties of the Earth and planets - from their deep interiors to their atmospheres. EPSL also includes a Frontiers section, featuring invited high-profile synthesis articles by leading experts on timely topics to bring cutting-edge research to the wider community.