[S-EM15] Geomagnetism and paleomagnetism

[SEM15-02] Rock-magnetic and paleomagnetic studies of returned samples from asteroid (162173) Ryugu

*Masahiko Sato¹, Yuki Kimura², Satoshi Tanaka³, Tadahiro Hatakeyama⁴, Seiji Sugita¹, Tomoki Nakamura⁵, Shogo Tachibana¹, Satoshi Okuzumi⁶, Sei-ichiro WATANABE⁷, Hisayoshi Yurimoto², Takaaki Noguchi⁸, Ryuji Okazaki⁹, Hikaru Yabuta¹⁰, Hiroshi Naraoka⁹, Sakamoto Kanako³, Toru Yada³, Masahiro Nishimura³, Aiko Nakato³, Akiko Miyazaki³, Kasumi Yogata³, Masanao Abe³, Tatsuaki Okada³, Tomohiro Usui³, Makoto Yoshikawa³, Takanao Saiki³, Fuyuto Terui¹¹, Satoru Nakazawa³, Yuichi Tsuda³ (1.The University of Tokyo, 2.Hokkaido University, 3.Japan Aerospace Exploration Agency, 4.Okayama University of Science, 5.Tohoku University, 6.Tokyo Institute of Technology, 7.Nagoya University, 8.Kyoto University, 9.Kyushu University, 10.Hiroshima University, 11.Kanagawa Institute of Technology)

Keywords:Asteroid (162173) Ryugu, Rock-magnetism, Paleointensity, Nebular magnetic field

Knowledge of the dynamical evolution of the solar nebula materials is key to understanding the history of the solar system. The magnetic field of the solar nebula was generated and sustained as the results of dynamics of weakly ionized nebular gas, and the materials in the solar nebula were dynamically interacted and coevolved with the magnetic field. Therefore, the nebular field information recorded in primordial materials gives critical constraint on the time-spatial evolution of the early solar system. The magnetic field of the early solar system have been reconstructed from the meteorite samples, while the time-spatial evolutions of the disk magnetism have not been fully constrained yet. Here we repot the results of rock-magnetic and paleomagnetic measurements for returned samples from C-type asteroid (162173) Ryugu, which offer a unique opportunity to investigate the magnetic field of the early solar system because they have been minimized the effects of chemical/mineralogical changes and magnetic field contamination on Earth. The Ryugu samples exhibit signatures for framboidal magnetite, coarse-grained magnetite, and pyrrhotite, and that framboidal magnetite is the dominant remanence carrier of Ryugu samples in the middle-coercivity range. The saturation isothermal remanent magnetization (SIRM) paleointensity constant was obtained for two Ryugu samples, close to the literature’s value based on the average among magnetite, titanomagnetite, pyrrhotite, and FeNi alloys and is widely used for SIRM paleointensity experiments. Four out of seven particles show the stable natural remanence components and the similar paleointensity values. On the basis of paleointensity record, we will discuss the dynamical evolution of Ryugu’s parent body.