Initial analyzes showed that the composition of asteroid Ryugu is close to CI (Ivuna-like) carbonaceous chondrites (CCs) – the most chemically primitive meteorites, characterized by near-solar abundances for most elements. However, some isotopic signatures (e.g., Ti, Cr) overlap with other CC groups, so the details of the link between Ryugu and the CI chondrites are not yet fully understood.

Nearly two years after the Japanese Hayabusa2 spacecraft made its way back to Earth, samples from the asteroid Ryugu continue to provide vital insight into the solar system’s early past. The isotopic composition of the zinc and copper in the asteroid Ryugu was determined by scientists from the Institut de Physique du Globe de Paris, Université Paris Cité and CNRS1 as part of an international collaboration.

The isotope signatures show that Ryugu’s composition is close to Ivuna-like carbonaceous chondrites and that Ryugu-like material from the outer solar system accounts for about 5-6% of Earth’s mass.

Two moderately volatile metals, zinc and copper, are essential to understanding volatile accretion processes during the formation of telluric planets. The varied zinc and copper isotope compositions of the different groups of carbonaceous chondrites can be seen, with the CI chondrites predominating in volatile elements. Additional analyzes of Ryugu’s zinc and copper isotope composition provided the scientists with an essential resource for understanding the asteroid’s formation.

The scientists showed that the isotope ratios of copper and zinc in the samples from Ryugu were identical to CI chondrites, but different from all other types of meteorites. This study confirms that these early samples from Ryugu provide the largest estimate of solar composition for copper and zinc by conclusively demonstrating the similarities between Ryugu and CI chondrites.

Finally, the development of planetary habitability can be understood by studying the accretion history of moderately volatile elements on Earth using Ryugu’s zinc isotope composition. The study also shows that about 5% of Earth’s mass comes from material similar to Ryugu.

Magazine reference:

  1. Paquet, M., Moynier, F., Yokoyama, T. et al. Contribution of Ryugu-like material to the Earth’s volatile inventory by Cu and Zn isotopic analysis. Wet Astron (2022). DOI: 10.1038/s41550-022-01846-1