[S-EM15] 地磁気・古地磁気・岩石磁気

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

*佐藤 雅彦¹、木村 勇気²、田中 智³、畠山 唯達⁴、杉田 精司¹、中村 智樹⁵、橘 省吾¹、奥住 聡⁶、渡邊 誠一郎⁷、圦本 尚義²、野口 高明⁸、岡崎 隆司⁹、薮田 ひかる¹⁰、奈良岡 浩⁹、坂本 佳奈子³、矢田 達³、西村 征洋³、中藤 亜衣子³、宮崎 明子³、与賀田 佳澄³、安部 正真³、岡田 達明³、臼井 寛裕³、吉川 真³、佐伯 孝尚³、照井 冬人¹¹、中澤 暁³、津田 雄一³ (1.東京大学、2.北海道大学、3.宇宙科学研究所、4.岡山理科大学、5.東北大学、6.東京工業大学、7.名古屋大学、8.京都大学、9.九州大学、10.広島大学、11.神奈川工科大学)

キーワード：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.