A. N. Nguyen, S. J. Clemett, K. Thomas-Keprta, C. M. O'D. Alexander, D. P. Glavin, J. P. Dworkin, H. C. Connolly Jr, D. S. Lauretta
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We analyzed acid-insoluble residues produced from two powdered samples of the Murchison carbonaceous chondrite, one control and one XCT-scanned, to assess the impact on insoluble organic matter (IOM) and presolar grains. Using a suite of in situ analytical techniques (field-emission scanning electron microscopy, optical and ultraviolet fluorescence microscopy, microprobe two-step laser mass spectrometry, and nanoscale secondary ion mass spectrometry), we found that the two residues had indistinguishable chemical, molecular, and isotopic signatures on the micron to submicron scale, indicating that an X-ray dosage of 180 Gy (the maximum dose to be used during preliminary examination of Bennu materials) did not damage the IOM and presolar grains. To explore the use of acid-insoluble residues to infer parent body processes in preparation for Bennu sample analysis, we also analyzed a residue produced from the Sutter's Mill carbonaceous chondrite. 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引用次数: 0
摘要
起源、光谱解读、资源识别和安全--红岩探测器(OSIRIS-REx)航天器返回的 B 型小行星(101955)贝努样本将为了解碳质小行星物质的性质提供独特的见解,而不会产生与陨石样本有关的大气进入加热或陆地风化效应。一些贝努样本将通过 X 射线计算机断层扫描(XCT)进行表征。为了保护样本的原始性质,必须了解 XCT 分析期间辐照可能造成的任何不利影响。我们分析了从默奇森碳质软玉的两个粉末样本(一个对照样本和一个XCT扫描样本)中产生的酸不溶性残留物,以评估其对不溶性有机物(IOM)和前极粒的影响。利用一套原位分析技术(场发射扫描电子显微镜、光学和紫外荧光显微镜、微探针两步激光质谱法和纳米级二次离子质谱法),我们发现这两种残留物在微米到亚微米尺度上具有难以区分的化学、分子和同位素特征,这表明 180 Gy 的 X 射线剂量(贝努材料初步检查期间使用的最大剂量)并没有损坏不溶性有机物质和前极粒。为了探索利用酸不溶性残留物来推断母体在准备贝努样本分析时的过程,我们还分析了从萨特磨坊碳质软玉中产生的残留物。多种证据(包括严重退化的紫外线荧光特征和富含D的热点)表明,萨特磨坊星的母体曾被加热到400°C。这一加热事件很可能持续时间很短,因为被热变质作用和长期氧化作用破坏的前极性碳化硅晶粒的丰度与默奇森和其他未加热软玉中的碳化硅晶粒的丰度一致。对来自默奇森和萨特磨坊的酸不溶性残留物进行的这些原位分析结果为批量分析提供了补充细节。
Micro- and nanoscale studies of insoluble organic matter and C-rich presolar grains in Murchison and Sutter's Mill in preparation for Bennu sample analysis
Samples of B-type asteroid (101955) Bennu returned by the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) spacecraft will provide unique insight into the nature of carbonaceous asteroidal matter without the atmospheric entry heating or terrestrial weathering effects associated with meteoritic samples. Some of the Bennu samples will undergo characterization by X-ray computed tomography (XCT). To protect the pristine nature of the samples, it is important to understand any adverse effects that could result from irradiation during XCT analysis. We analyzed acid-insoluble residues produced from two powdered samples of the Murchison carbonaceous chondrite, one control and one XCT-scanned, to assess the impact on insoluble organic matter (IOM) and presolar grains. Using a suite of in situ analytical techniques (field-emission scanning electron microscopy, optical and ultraviolet fluorescence microscopy, microprobe two-step laser mass spectrometry, and nanoscale secondary ion mass spectrometry), we found that the two residues had indistinguishable chemical, molecular, and isotopic signatures on the micron to submicron scale, indicating that an X-ray dosage of 180 Gy (the maximum dose to be used during preliminary examination of Bennu materials) did not damage the IOM and presolar grains. To explore the use of acid-insoluble residues to infer parent body processes in preparation for Bennu sample analysis, we also analyzed a residue produced from the Sutter's Mill carbonaceous chondrite. Multiple lines of evidence, including severely degraded UV fluorescence signatures and D-rich hotspots, indicate that the parent body of Sutter's Mill was heated to >400°C. This heating event was likely short lived because the abundance of presolar SiC grains, which are destroyed by thermal metamorphism and prolonged oxidation, was consistent with those in Murchison and other unheated chondrites. The results of these in situ analyses of acid-insoluble residues from Murchison and Sutter's Mill provide complementary detail to bulk analyses.
期刊介绍:
First issued in 1953, the journal publishes research articles describing the latest results of new studies, invited reviews of major topics in planetary science, editorials on issues of current interest in the field, and book reviews. The publications are original, not considered for publication elsewhere, and undergo peer-review. The topics include the origin and history of the solar system, planets and natural satellites, interplanetary dust and interstellar medium, lunar samples, meteors, and meteorites, asteroids, comets, craters, and tektites. Our authors and editors are professional scientists representing numerous disciplines, including astronomy, astrophysics, physics, geophysics, chemistry, isotope geochemistry, mineralogy, earth science, geology, and biology. MAPS has subscribers in over 40 countries. Fifty percent of MAPS'' readers are based outside the USA. The journal is available in hard copy and online.