Ryugu: Asteroid samples continue to shed light on the history of the solar system

Nearly two years after the Japanese mission Hayabusa2 returned to Earth, samples from the asteroid Ryugu continue to reveal valuable information about the history of the early solar system.

A study conducted by scientists from the Institut de Physique du Globe de Paris, Université Paris Cité and CNRS1, as part of an international consortium, reveals the isotopic composition of zinc and copper from the asteroid Ryugu . 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. These results are published on December 12, 2022 in the journal natural astronomy.

Meteorites found on Earth give scientists access to samples representing the earliest moments of the solar system. However, the return to Earth in December 2020 of the Hayabusa2 mission, operated by the Japanese space agency JAXA and bringing back 5 grams of fragments from the asteroid Ryugu, marks a major step forward by offering the possibility of analyzing samples not altered by their arrival and stay on Earth.

The first analyses, carried out by an international team, including researchers from the Institut de physique du globe de Paris, the Université Paris Cité and the CNRS, have shown that the composition of the asteroid Ryugu is close to that of chondrites. carbonaceous type Ivuna (CI) – the most chemically primitive meteorites and considered to have the composition closest to the sun. However, some isotopic signatures (e.g., titanium and chromium) overlap with other groups of carbonaceous chondrites, so the details of the link between Ryugu and CI chondrites are not yet fully understood.

Zinc and copper are two moderately volatile elements, and are key elements for studying the processes of accretion of volatiles during the formation of telluric planets. The different groups of carbonaceous chondrites show distinct isotopic compositions of zinc and copper, with the CI chondrites being the richest in volatile elements. By carrying out further analyzes of the zinc and copper isotopic composition of Ryugu, the scientists gained access to a crucial tool for studying the origin of the asteroid.

The international team showed, in a study published on December 12, 2022 in the journal natural astronomy and led by Marine Paquet and Frédéric Moynier, cosmochemists at the IPGP, that the isotopic ratios of copper and zinc in the Ryugu samples were identical to CI chondrites but different from all other types of meteorites.

Finally confirming the similarity between Ryugu and CI chondrites, this study establishes that these early samples from Ryugu represent the best estimate of solar composition to date for copper and zinc.

Finally, the isotopic composition of zinc from Ryugu can also be used to study the accretion history of moderately volatile elements on Earth, essential for the development of planetary habitability. The study also demonstrates that the contribution of Ryugu-type materials represents about 5% of the earth’s mass.