Anomalously porous boulders on (162173) Ryugu as primordial materials from its parent body-猫眼课题宝

DOI：

10.1038/s41550-021-01371-7

发表时间：

2021-05

期刊：

Nature Astronomy

影响因子：

14.1

通讯作者：

中科院分区：

物理与天体物理1区

文献类型：

作者：

N. Sakatani;Satoshi Tanaka;T. Okada;T. Fukuhara;L. Riu;S. Sugita;R. Honda;T. Morota;S. Kameda;Y. Yokota;E. Tatsumi;K. Yumoto;N. Hirata;A. Miura;T. Kouyama;H. Senshu;Y. Shimaki;T. Arai;J. Takita;H. Demura;T. Sekiguchi;T. Müller;A. Hagermann;J. Biele;M. Grott;M. Hamm;M. Delbo’;W. Neumann;M. Taguchi;Y. Ogawa;T. Matsunaga;T. Wada;S. Hasegawa;J. Helbert;R. Noguchi;M. Yamada;H. Suzuki;C. Honda;K. Ogawa;M. Hayakawa;K. Yoshioka;M. Matsuoka;Yuichiro Cho;H. Sawada;K. Kitazato;T. Iwata;M. Abe;M. Ohtake;S. Matsuura;Koji Matsumoto;H. Noda;Y. Ishihara;K. Yamamoto;A. Higuchi;N. Namiki;G. Ono;T. Saiki;H. Imamura;Y. Takagi;H. Yano;K. Shirai;C. Okamoto;S. Nakazawa;Y. Iijima;M. Arakawa;K. Wada;T. Kadono;K. Ishibashi;F. Terui;S. Kikuchi;Tomohiro Yamaguchi;N. Ogawa;Y. Mimasu;K. Yoshikawa;T. Takahashi;Y. Takei;A. Fujii;H. Takeuchi;Yukio Yamamoto;C. Hirose;S. Hosoda;O. Mori;T. Shimada;S. Soldini;R. Tsukizaki;M. Ozaki;S. Tachibana;H. Ikeda;M. Ishiguro;H. Yabuta;M. Yoshikawa;Sei‐ichiro Watanabe;Y. Tsuda

星子是行星形成过程的初始阶段，最初被认为是非常多孔的尘埃聚集体，随后的热和压实过程降低了它们的孔隙度。隼鸟2号宇宙飞船发现，小行星（162173）Ryugu表面的巨石平均孔隙率为30-50%（参考文献，- ），比陨石高但比彗星核低，彗星核被认为是原始星子的残余。在这里，我们使用高分辨率的热成像和光学成像对Ryugu的表面进行了研究，在新鲜的小陨石坑（直径<20米）的底部，我们发现了反射率（~0.015）低于Ryugu平均值的巨石，孔隙度> 70%，这与彗星体一样高。隼鸟2号撞击实验形成的人工陨石坑与这些陨石坑大小相似，但没有如此高孔隙度的巨石。因此，我们认为，所观察到的高孔隙率是内在的，而不是由随后的冲击粉碎和/或开裂。我们认为这些巨石是Ryugu上加工最少的材料，代表了没有经历高度加热和压实的多孔微行星的残余物。我们的多仪器分析表明，高度多孔的巨石碎片混合在全球的表面风化层，这意味着它们可能被捕获在收集的样品中的着陆操作，。

Planetesimals—the initial stage of the planetary formation process—are considered to be initially very porous aggregates of dusts,, and subsequent thermal and compaction processes reduce their porosity. The Hayabusa2 spacecraft found that boulders on the surface of asteroid (162173) Ryugu have an average porosity of 30–50% (refs., –), higher than meteorites but lower than cometary nuclei, which are considered to be remnants of the original planetesimals. Here, using high-resolution thermal and optical imaging of Ryugu’s surface, we discovered, on the floor of fresh small craters (<20 m in diameter), boulders with reflectance (~0.015) lower than the Ryugu average and porosity >70%, which is as high as in cometary bodies. The artificial crater formed by Hayabusa2’s impact experiment is similar to these craters in size but does not have such high-porosity boulders. Thus, we argue that the observed high porosity is intrinsic and not created by subsequent impact comminution and/or cracking. We propose that these boulders are the least processed material on Ryugu and represent remnants of porous planetesimals that did not undergo a high degree of heating and compaction. Our multi-instrumental analysis suggests that fragments of the highly porous boulders are mixed within the surface regolith globally, implying that they might be captured within collected samples by touch-down operations,.

Anomalously porous boulders on (162173) Ryugu as primordial materials from its parent body

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