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*Free* Samples from Ryugu are chemically similar to Ivuna-type carbonaceous meteorites

Peer-Reviewed Publication

American Association for the Advancement of Science (AAAS)

Samples recovered from near-Earth asteroid Ryugu are chemically similar to Ivuna-type (CI) carbonaceous meteorites, according to a new study. CI chondrites provide a unique opportunity to understand the formation of the Solar System as their elemental composition more closely matches measurements of the solar photosphere than other types of meteorites. The authors suggest that the samples from Ryugu represent chemically the most primitive and pristine Solar System materials yet analyzed in a laboratory, including other CI meteorites found on Earth. From June to November 2019, Hayabusa2 investigated Ryugu, characterizing the asteroid from orbit and collecting samples of its rocky surface for return to Earth. Two landing operations were performed: one which sampled the material on Ryugu’s surface and another that collected sub-surface material excavated by an artificial impact experiment. In December 2020, Hayabusa2 delivered roughly five grams of material to Earth. Preliminary analyses of the returned samples from Ryugu demonstrated that their colors, shapes, and morphologies were consistent with those observed on the asteroid’s surface, suggesting that the material is representative of Ryugu’s surface. Here, Tetsuya Yokoyama and colleagues report the mineralogical, bulk chemical, and isotopic characteristics of the Ryugu samples. Using a variety of analytical tools, including electron microscopy, x-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS), and thermal ionization mass spectrometry (TIMS) on polished sections of particle samples from both Hayabusa2 landing sites, Yokoyama and colleagues discovered that the samples are mainly composed of materials similar to Ivuna-type (CI) carbonaceous chondrite meteorites. According to the findings, the samples primarily consist of minerals likely formed in aqueous fluid on a parent planetesimal roughly 5 million years after Solar System formation.

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