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Ryugu asteroid: It came from the outer solar system, say scientists

Japanese Hayabusa-2 probe samples reveal coarse-grained phyllosilicates that may have served as 'cradles' for organics and water

Scientists examining samples from the asteroid Ryugu retrieved by the Japanese Hayabusa-2 probe have concluded that Ryugu is a drifter from the outer solar system.

The results, published in Nature Astronomy, come after just over a year of initial analysis conducted by institutes and universities across Japan, the UK, and USA.

The team, led by Motoo Ito of the Extra-cutting-edge Science and Technology Avant-garde Research (X-star), Kochi Institute for Core Sample Research, kicked off their analysis on June 20, 2021, following an initial cataloging phase.

Getting up close and personal with asteroids in space gives scientists insight into the building blocks of the solar system. Peering at those that fall to Earth as meteorites doesn't quite cut it in comparison, since the inevitable interaction with the Earth's atmosphere tends to result in alterations to the chemical composition of materials.

The team said: "By collecting samples directly from asteroid Ryugu and delivering them to Earth free from terrestrial contamination, the JAXA Hayabusa2 mission has provided scientists with the opportunity to study contamination-free, primitive samples for the very first time."

The results make for interesting reading. "Aliphatic carbon-rich organics associated with coarse-grained phyllosilicates were found," noted scientists, something not observed in previous meteorite studies and "could be unique to the asteroid Ryugu."

More excitingly, "the results suggest that coarse-grained phyllosilicates may have served as 'cradles' for organics and water, which may subsequently have been transported to the early Earth."

The Kochi team were allocated 50mg of Ryugu pieces in the form of eight particles (with diameters ranging from one to four millimeters). Studies of the Ryugu samples have already found all manner of exciting stuff, ranging from reports of amino acids to organic matter. The latest findings will only add to the excitement, particularly considering NASA's OSIRIS-REx asteroid probe is due to drop its samples from Bennu back to Earth next year.

"Mineral assemblages in the Ryugu particles are consistent with having formed in the presence of water," said scientists, "suggesting that ice (water) existed on/within the Ryugu parent body in the past and that the minerals formed as a result of the reaction between water (liquid) and the original minerals."

Since Ryugu has never experienced significant heating, according to the study, it has retained its primitive characteristics.

Naturally, scientists are keen to keep on investigating the samples, as well as stirring in the results of whatever was collected from Bennu. For now, the findings conclude that Ryugu accreted components from the outer solar system (containing water and organics) and traveled to the inner solar system.

Asteroids like it (C-type asteroids) could well have been one of the sources of Earth's water. ®

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