Kimura Yuki, Kato Takeharu, Anada Satoshi, Yoshida Ryuji, Yamamoto Kazuo, Tanigaki Toshiaki, Akashi Tetsuya, Kasai Hiroto, Kurosawa Kosuke, Nakamura Tomoki, Noguchi Takaaki, Sato Masahiko, Matsumoto Toru, Morita Tomoyo, Kikuiri Mizuha, Amano Kana, Kagawa Eiichi, Yada Toru, Nishimura Masahiro, Nakato Aiko, Miyazaki Akiko, Yogata Kasumi, Abe Masanao, Okada Tatsuaki, Usui Tomohiro, Yoshikawa Makoto, Saiki Takanao, Tanaka Satoshi, Terui Fuyuto, Nakazawa Satoru, Yurimoto Hisayoshi, Okazaki Ryuji, Yabuta Hikaru, Naraoka Hiroshi, Sakamoto Kanako, Watanabe Sei-Ichiro, Tsuda Yuichi, Tachibana Shogo
Institute of Low Temperature Science, Hokkaido University, Sapporo, 060-0819, Japan.
Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya, 456-8587, Japan.
Nat Commun. 2024 Apr 29;15(1):3493. doi: 10.1038/s41467-024-47798-0.
Extraterrestrial minerals on the surface of airless Solar System bodies undergo gradual alteration processes known as space weathering over long periods of time. The signatures of space weathering help us understand the phenomena occurring in the Solar System. However, meteorites rarely retain the signatures, making it impossible to study the space weathering processes precisely. Here, we examine samples retrieved from the asteroid Ryugu by the Hayabusa2 spacecraft and discover the presence of nonmagnetic framboids through electron holography measurements that can visualize magnetic flux. Magnetite particles, which normally provide a record of the nebular magnetic field, have lost their magnetic properties by reduction via a high-velocity (>5 km s) impact of a micrometeoroid with a diameter ranging from 2 to 20 μm after destruction of the parent body of Ryugu. Around these particles, thousands of metallic-iron nanoparticles with a vortex magnetic domain structure, which could have recorded a magnetic field in the impact event, are found. Through measuring the remanent magnetization of the iron nanoparticles, future studies are expected to elucidate the nature of the nebular/interplanetary magnetic fields after the termination of aqueous alteration in an asteroid.
在无大气的太阳系天体表面，外星矿物会经历漫长的逐渐变化过程，即所谓的空间风化。空间风化的特征有助于我们了解太阳系中发生的现象。然而，陨石很少保留这些特征，这使得精确研究空间风化过程变得不可能。在此，我们检查了隼鸟2号航天器从小行星龙宫取回的样本，并通过能够可视化磁通量的电子全息测量发现了非磁性莓球粒的存在。通常能记录星云磁场的磁铁矿颗粒，在龙宫母体被摧毁后，由于直径为2至20微米的微流星体以高速（>5千米/秒）撞击而通过还原作用失去了磁性。在这些颗粒周围，发现了数千个具有涡旋磁畴结构的金属铁纳米颗粒，它们可能在撞击事件中记录了磁场。通过测量铁纳米颗粒的剩余磁化强度，预计未来的研究将阐明小行星上水成蚀变终止后星云/行星际磁场的性质。
