Breunnerite grain and magnesium isotope chemistry reveal cation partitioning during aqueous alteration of asteroid Ryugu

Key points of the results:

The tiny Mg-bearing carbonate grains (breunnerite) of the Ryugu asteroid sample was isolated and identified, and the Mg isotopic composition was measured using high-precision isotope mass spectrometry. By calculating the fractionation of Mg isotopes, we were able to determine the precipitation order of Mg-bearing minerals, including carbonates that formed as a secondary mineral during the process of interaction between the primary rock and water (aqueous alteration) on Ryugu.

The composition of the primordial brine was clarified by extracting samples collected from the asteroid Ryugu with multiple types of solvent. We found that sodium ions (Na⁺) were the most abundant dissolved cation component due to the interaction between water and minerals.

The presence of bittern components such as Mg²⁺ in the solutes of brine is important for stabilizing soluble organic matter. The findings of this research are important for exploring how materials existed in the solar system before the formation of the Earth and for investigating its chemical evolution.

For more details, please see the Nature Communication link:
DOI: 10.1038/s41467-024-50814-y

By analyzing the chemical composition of secondary minerals such as breunnerite (microscope image at bottom right) brought back by the asteroid explorer Hayabusa2 from the asteroid Ryugu, the solute composition of brine and the history of mineral precipitation have been revealed. Toshihiro Yoshimura, Researcher,