¹Kazuhiko Ninomiya et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14135]
¹Institute for Radiation Sciences, Osaka University, Toyonaka, Japan
Published by arrangement with John Wiley & Sons

Samples from asteroid Ryugu, brought back by asteroid explorer Hayabusa2, are important for investigating the origin and evolution of the solar system. Here, we report the elemental compositions of a 123-mg Ryugu sample determined with a nondestructive muon elemental analysis method. This method is a powerful tool for determining bulk chemical composition, including light elements such as C, N, and O. From the muonic x-ray spectra with three carbonaceous chondrites, the relationship between the elemental composition and muonic x-ray intensity was determined for each element. Calibration curves showed linearity, and the elemental composition of Ryugu was quantitatively determined. The results reflect the average bulk elemental composition of asteroid Ryugu owing to the large amount of samples. Ryugu has an elemental composition similar to that of Orgueil (CI1) and should be classified as CI1. However, the O/Si ratio of Ryugu is 25% lower than that of Orgueil, indicating that Orgueil may have been seriously contaminated by terrestrial materials after its fall to Earth. These results indicate that the Ryugu sample is more representative than the CI chondrites as a solid material of the solar system.

^1,2Ting Cao,²Huapei Wang,²Shaochen Hu,^3,4Kaixian Qi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14136]
¹School of Earth Sciences, China University of Geosciences, Wuhan, Hubei, China
²Paleomagnetism and Planetary Magnetism Laboratory, School of Geophysics and Geomatics, China University of Geosciences, Wuhan, Hubei, China
³State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
⁴College of Earth and Planetary Sciences, University of the Chinese Academy of Sciences, Beijing, China
Published by arrangement with John Wiley & Sons

We present the first rock magnetic and paleomagnetic analyses of the Martian meteorite Grove Mountains (GRV) 020090, a suitable candidate for paleomagnetic study due to its low degree of weathering and shock metamorphism. Petrological and rock magnetic investigation indicates that pyrrhotite is the dominant magnetic mineral in GRV 020090, where it occurs as a primary phase without significant shock metamorphism or alteration. The magnetic grains in GRV 020090 exhibit single-domain behavior that facilitates high-fidelity magnetic recording. We obtained a positive fusion-crust baked contact test, which supports an extraterrestrial origin of the primary remanence in GRV 020090. The nature of the primary remanence was identified as thermoremanence acquired during crystallization of the rock on Mars. Anhysteretic remanent magnetization and isothermal remanent magnetization paleointensity methods indicated paleofield strengths of 1.6 and 2.6 μT, respectively, for the primary remanence. However, the shock pressure that GRV 020090 experienced may have partially demagnetized the primary remanence, leading to underestimated paleointensity values. Therefore, 1.6 μT is regarded as the lower limit on the paleointensity of GRV 020090. This lower limit is higher than the model-predicted surface magnetic field strength in the source region for GRV 020090, suggesting that it may have recorded a small-scale crustal magnetic field previously undetected by orbital magnetic data. This small-scale crustal field is likely generated by the underlying ancient, magnetized layers, as the crustal magnetization of the surficial terrane with lithology similar to GRV 020090 is too weak to produce such a crustal field.