近日，东京大学Tsuyoshi Iizuka团队报道了Ryugu中Lu-Hf同位素揭示的原始小行星中的晚期流体流动。2025年9月10日出版的《自然》杂志发表了这项成果。

碳源小行星是最原始陨石的存在，代表了太阳系外由冰和冰形成的残余的星子，它们可能向类地行星输送挥发物。了解小行星上的水系活动是破译它们的热、化学和轨道演化的关键，对类地行星上水的起源也有影响。对这些物体的分析，特别是从小行星Ryugu带回的原始样本，提供了在母体形成后几百万年内流体-岩石相互作用的详细信息。然而，人们对小行星水的长期命运仍然知之甚少。

研究组提供了碳质小行星中流体流动的证据， 根据Ryugu样品的¹⁷⁶Lu–¹⁷⁶Hf衰变系统学，这反映了后期的镥动员。这种晚期的流体流动可能是由一种撞击引发的，这种撞击产生了冰融化的热量，并打开了岩石裂缝以进行流体迁移。这与早期由短寿命放射性衰变驱动的水性活动形成鲜明对比，流体流动有限，元素分馏很少。该研究结果表明，由类地行星吸积的碳质星子不仅可能保留了含水矿物，还可能保留了水，导致其输水量增加了两到三倍。

附：英文原文

Title: Late fluid flow in a primitive asteroid revealed by Lu–Hf isotopes in Ryugu

Author: Iizuka, Tsuyoshi, Shibuya, Takazo, Hayakawa, Takehito, Yokoyama, Tetsuya, Gautam, Ikshu, Haba, Makiko K., Ito, Kengo T. M., Hibiya, Yuki, Yamaguchi, Akira, Abe, Yoshinari, Alon, Jrme, Alexander, Conel M. OD., Amari, Sachiko, Amelin, Yuri, Bajo, Ken-ichi, Bizzarro, Martin, Bouvier, Audrey, Carlson, Richard W., Chaussidon, Marc, Choi, Byeon-Gak, Dauphas, Nicolas, Davis, Andrew M., Di Rocco, Tommaso, Fujiya, Wataru, Fukai, Ryota, Hidaka, Hiroshi, Homma, Hisashi, Huss, Gary R., Ireland, Trevor R., Ishikawa, Akira, Itoh, Shoichi, Kawasaki, Noriyuki, Kita, Noriko T., Kitajima, Koki, Kleine, Thorsten, Komatani, Shintaro, Krot, Alexander N., Liu, Ming-Chang, Masuda, Yuki, Motomura, Kazuko, Moynier, Frdric, Nagashima, Kazuhide, Nakai, Izumi, Nguyen, Ann, Nittler, Larry, Pack, Andreas, Park, Changkun, Piani, Laurette, Qin, Liping, Russell, Sara, Sakamoto, Naoya, Schnbchler, Maria, Tafla, Lauren, Tang, Haolan, Terada, Kentaro, Terada, Yasuko, Usui, Tomohiro, Wada, Sohei, Wadhwa, Meenakshi, Walker, Richard J., Yamashita, Katsuyuki, Yin, Qing-Zhu, Yoneda, Shigekazu, Yui, Hiroharu, Zhang, Ai-Cheng, Nakamura, Tomoki, Naraoka, Hiroshi, Noguchi, Takaaki, Okazaki, Ryuji, Sakamoto, Kanako, Yabuta, Hikaru, Abe, Masanao, Miyazaki, Akiko

Issue&Volume: 2025-09-10

Abstract: Carbonaceous asteroids are the source of the most primitive meteorites1 and represent leftover planetesimals that formed from ice and dust in the outer Solar System and may have delivered volatiles to the terrestrial planets2,3,4,5. Understanding the aqueous activity of asteroids is key to deciphering their thermal, chemical and orbital evolution, with implications for the origin of water on the terrestrial planets. Analyses of the objects, in particular pristine samples returned from asteroid Ryugu, have provided detailed information on fluid–rock interactions within a few million years after parent-body formation6,7,8,9,10,11. However, the long-term fate of asteroidal water remains poorly understood. Here we present evidence for fluid flow in a carbonaceous asteroid more than 1billion years after formation, based on the 176Lu–176Hf decay systematics of Ryugu samples, which reflect late lutetium mobilization. Such late fluid flow was probably triggered by an impact that generated heat for ice melting and opened rock fractures for fluid migration. This contrasts the early aqueous activity powered by short-lived radioactive decay, with limited fluid flow and little elemental fractionation12. Our results imply that carbonaceous planetesimals accreted by the terrestrial planets could have retained not only hydrous minerals but also aqueous water, leading to an upwards revision of the inventory of their water delivery by a factor of two to three.

DOI: 10.1038/s41586-025-09483-0

Source: https://www.nature.com/articles/s41586-025-09483-0