A chunk of space rock may hold clues to origin of Earth

A sample of a space rock called Ryugu that returned to Earth almost two years ago may hold the answers to the origin of the planet, according to a new study. 

Roughly 5 per cent of materials that assembled to form Earth more than 4.5 billion years ago could have come from space rocks similar to near-Earth asteroid Ryugu, found a study published in the journal Nature Astronomy.

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Samples of Ryugu were carried to Earth in 2020 by the Japanese space agency’s asteroid sample-return mission, Hayabusa 2. The mission was launched in 2014.

“It is the first time several grams of asteroid samples were brought back to Earth,” Marine Paquet, a postdoctoral researcher at the Institut de Physique du Globe de Paris and one of the study’s authors, told Down To Earth.

These asteroid samples, she added, represent the first solids to be formed in the solar system. This means they could be the building blocks of Earth.

Though meteorites falling into Earth give scientists a peek into the solar system’s origin, they are often contaminated. Ryugu samples, on the other, were carefully handled to avoid possible contamination, the researchers wrote in their study. 

This makes these samples valuable for estimating the solar system’s building blocks, the paper read. These samples could also help evaluate the role of Ryugu-like objects in depositing volatile elements to terrestrial planets.

Volatile elements such as hydrogen, carbon, nitrogen and oxygen are thought to have played a key role in forging complex organic molecules — ingredients essential to build habitable worlds like Earth, according to researchers.

Paquet and her colleagues studied the isotopic composition of two volatile elements: Zinc and copper.

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Their analysis of isotopic ratios of zinc and copper showed that Ryugu was similar in composition to CI chondrites. They are a group of rare carbonaceous chondrite (CC), a type of stony meteorite.

“We show that Ryugu has copper and zinc isotope ratios similar to a very rare group of meteorites that are likely the most primitive (ones with the closest composition to the Sun),” Paquet explained.

They are primitive because they likely formed in the outer solar system, where volatile elements are preserved. In contrast, materials created closer to the Sun may have lost a part of their volatile inventory due to evaporation, the expert explained.

These findings are consistent with another related study published in journal Science Advances on October 22, 2022.

Timo Hopp, a planetary scientist at the Max Planck Institute for Solar System Research in Germany, and his colleagues studied iron isotopes in Ryugu samples.

The analysis showed that Ryugu formed in the same reservoir as CI chondrites and not with other CC.

The reservoir that created Ryugu and CI chondrites could be outside the solar system, Hopp told DTE. It is possible that Saturn or Uranus separated the two reservoirs, he added. 

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Paquet also agreed that Ryugu and CI chondrites have the same origin. But, she added, these findings don’t necessarily mean that the CI chondrite asteroid is Ryugu. 

Further, “when the Earth formed 4.57 billion years ago, about 5 per cent of the agglomerated materials were similar to Ryugu,” Paquet highlighted. It may have brought the bricks necessary to the origin of life to Earth, she added.

The expert hopes to evaluate whether Ryugu-type materials also contributed to the origin of Mars.

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