Giant micrometeorites (MMs; 400–2000 µm) are exceedingly rare and scientifically valuable. Three‐dimensional nondestructive characterization by X‐ray computed tomography (X‐CT) provides information on the petrography and thus petrogenesis of MMs and serves as a guide to maximize subsequent multi‐analytical studies on such precious planetary materials. Here, we discuss the results obtained by X‐CT on 22 giant MMs and the classification based on their 3‐D density contrast images. Scoriaceous and unmelted MMs have distinct porosity ranges (10–40 vol% versus 0–25 vol%, respectively). We observe a porosity variation inside scoriaceous MMs, which allows their atmospheric entry flight history to be resolved. For the first time, spinning entry is explicitly demonstrated for four partially melted MMs. Furthermore, we are able to resolve the thermal gradient in a single particle, based on porosity variation (seen as a progressive increase in pore abundance and size with higher peak temperatures). Moreover, we explore parent body alteration through the 3‐D analysis of pores distribution, showing that shock fabrics are either absent or weakly developed in our data set. Finally, owing to the detection of pseudomorphic chondrules, we estimate that the intensively aqueously altered C1 or CI‐like material could represent 18% of the MM flux at this size fraction (400–1000 µm).

中文翻译：

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X射线计算机断层扫描：南极巨型陨石的形态学和孔隙率表征

巨型微陨石（MM； 400-2000 µm）极为稀少，具有科学价值。通过X射线计算机断层扫描（X-CT）进行的三维无损表征提供了有关岩石学的信息，从而提供了MM的岩石成因的信息，并为最大程度地进行后续关于此类珍贵行星材料的多分析研究提供了指导。在这里，我们讨论X-CT在22个巨型MM上获得的结果，以及基于其3D密度对比图像进行的分类。针状和未熔融的MM具有不同的孔隙率范围（分别为10–40 vol％和0–25 vol％）。我们观察到针状MM的内部孔隙率变化，这使得它们的大气进入飞行历史得以解决。首次明确证明了四个部分熔化的MM的纺丝入口。此外，我们能够根据孔隙率变化（在较高的峰值温度下，孔隙度和尺寸逐渐增加）来解析单个颗粒中的热梯度。此外，我们通过毛孔分布的3D分析探索了母体的变化，表明在我们的数据集中缺少防震织物或开发性较弱。最后，由于检测到拟态软骨，我们估计，在此尺寸分数（400–1000 µm）下，经过强水蚀的C1或CI样物质可代表MM通量的18％。表明在我们的数据集中没有或没有开发出防震织物。最后，由于检测到伪晶状体，我们估计在此尺寸分数（400-1000 µm）下，经过强水蚀的C1或CI样物质可代表MM通量的18％。表明在我们的数据集中缺少防震织物或防震织物的开发能力较弱。最后，由于检测到伪晶状体，我们估计在此尺寸分数（400-1000 µm）下，经过强水蚀的C1或CI样物质可代表MM通量的18％。