Presolar Stardust in Asteroid Ryugu
Presolar Stardust in Asteroid Ryugu
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DOI：
10.3847/2041-8213/ac83bd
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发表时间：
2022-08-01
影响因子：
7.9
通讯作者：
Yurimoto, Hisayoshi
中科院分区：
文献类型：
--
作者：
Barosch, Jens;Nittler, Larry R.;Yurimoto, Hisayoshi
作为日本宇宙航空研究开发机构隼鸟2号使命的一部分，我们对最近从C型小行星Ryugu返回的样本中的太阳前物质进行了基于NanoSIMS的搜索。我们报告的所有主要presolar颗粒类型的检测与O-和C-异常同位素组成通常确定在碳质球粒陨石：1硅酸盐，1氧化物，1 O-异常超新星颗粒的模糊相，38 SiC，和16碳质颗粒。至少有两个碳质颗粒是前太阳石墨，而几个颗粒与中度C同位素异常可能是有机物。presolar硅酸盐位于一个碎屑与较少改变的岩性比典型的广泛含水蚀变Ryugu矩阵。Ryugu的基质标准化前太阳颗粒丰度为O-异常颗粒4.8（-2.6）（+4.7）ppm，SiC颗粒25（-）（5）（+）（6）ppm，碳质颗粒11（-3）（+5）ppm。Ryugu在同位素和岩石学上与碳质Ivuna型（CI）辉长岩相似。为了比较在原地的前太阳的颗粒丰度Ryugu与CI的钙钛矿，我们还绘制了Ivuna和Orgueil样品，并发现了15个SiC颗粒和6个碳质颗粒。未发现O-异常颗粒。CI陨石中基质标准化的前太阳颗粒丰度与Ryugu相似：23（-6）（+7）ppm SiC和9.0（+5.4）（-3）（.6）ppm碳质颗粒。因此，我们的研究结果提供了进一步的证据支持Ryugu-CI连接。它们还揭示了Ryugu样本中小规模异质性的有趣线索，例如局部不同程度的改变，使微妙的前太阳物质得以保存。
We have conducted a NanoSIMS-based search for presolar material in samples recently returned from C-type asteroid Ryugu as part of JAXA's Hayabusa2 mission. We report the detection of all major presolar grain types with O- and C-anomalous isotopic compositions typically identified in carbonaceous chondrite meteorites: 1 silicate, 1 oxide, 1 O-anomalous supernova grain of ambiguous phase, 38 SiC, and 16 carbonaceous grains. At least two of the carbonaceous grains are presolar graphites, whereas several grains with moderate C isotopic anomalies are probably organics. The presolar silicate was located in a clast with a less altered lithology than the typical extensively aqueously altered Ryugu matrix. The matrix- normalized presolar grain abundances in Ryugu are 4.8(-2.6)(+4.7) ppm for O-anomalous grains, 25(-)(5)(+)(6) ppm for SiC grains, and 11(-3)(+5) ppm for carbonaceous grains. Ryugu is isotopically and petrologically similar to carbonaceous Ivuna-type (CI) chondrites. To compare the in situ presolar grain abundances of Ryugu with CI chondrites, we also mapped Ivuna and Orgueil samples and found a total of 15 SiC grains and 6 carbonaceous grains. No O-anomalous grains were detected. The matrix-normalized presolar grain abundances in the CI chondrites are similar to those in Ryugu: 23(-6)(+7) ppm SiC and 9.0 (+5.4)(-3)(.6) ppm carbonaceous grains. Thus, our results provide further evidence in support of the Ryugu-CI connection. They also reveal intriguing hints of small-scale heterogeneities in the Ryugu samples, such as locally distinct degrees of alteration that allowed the preservation of delicate presolar material.