Rock magnetic characterization of returned samples from asteroid (162173) Ryugu: Implications for paleomagnetic interpretation and paleointensity estimation

26/10/2022 10:46 · by karmaka · in asteroid, carbonaceous chondrite, Cb-type, CI, early chronology, OSIRIS-REx / 101955 Bennu, paleomagnetism, solar system, space missions, Tagish Lake

Masahiko Sato, Yuki Kimura, Satoshi Tanaka, Tadahiro Hatakeyama, Seiji Sugita, Tomoki Nakamuna, Shogo Tachibana, Hisayoshi Yurimoto, Takaaki Noguchi, Ryuji Okazaki, Hikaru Yabuta, Hiroshi Naraoka, Kanako Sakamoto, Toru Yada, Masahiro Nishimura, Aiko Nakato, Akiko Miyazaki, Kasumi Yogata, Masanao Abe, Tatsuaki Okada, Tomohiro Usui, Makoto Yoshikawa, Takanao Saiki, Fuyuto Terui, Satoru Nakazawa, Sei-ichiro Watanabe, Yuichi Tsuda

JGR: Planets
First Published: 24 October 2022

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“Key Points

Rock magnetic properties and paleointensity constant are investigated for returned samples from C-type asteroid (162173) Ryugu
Framboidal magnetites dominate stable natural remanence components of Ryugu samples in a middle-coercivity range
Paleointensity values estimated using our paleointensity constant indicate a strong magnetic field of the protoplanetary disk”

“In this study, systematic rock magnetic measurements and saturation isothermal remanent magnetization (SIRM) paleointensity calibration experiments were conducted for the returned samples from C-type asteroid (162173) Ryugu and two carbonaceous chondrites (Orgueil and Tagish Lake) to evaluate the remanence carriers of the Ryugu sample and its ability as a paleomagnetic recorder. Our magnetic measurements show that 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 SIRM paleointensity constant was obtained for two Ryugu samples, and the median value was 3318 ± 1038 μT, which is 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. The paleointensity values estimated using the obtained SIRM paleointensity constant indicate a strong magnetic field of the protoplanetary disk, suggesting that Sun’s protoplanetary disk existed at the disk location of Ryugu’s parent planetesimal when framboidal magnetite precipitated from the aqueous fluid.”