Asteroid Ryugu samples reveal their secrets

On the morning of December 6, 2020, in a desert area in southern Australia, a precious package that fell from the sky was recovered. After more than a year of travel and millions of kilometers traveled, the Japanese space agency’s Hayabusa-2 probe dropped on Earth a cargo of 5.4 grams taken from the asteroid Ryugu at two times, the February 22 and July 11, 2019.

This celestial body in the shape of a top, 1 kilometer wide, inflated with an equatorial bead and pockmarked with thousands of rocks several meters in diameter, rotates at a distance of between 140 and 210 million kilometers from the Sun, in a fairly large orbit. close to that of Earth. It could be one of the witness fossils of the early ages of the formation of the Solar System. When the gases and dust from the disk around the Sun began to aggregate into larger bodies, before shattering between them, to give smaller bodies, like asteroids, and the bricks that will make the planets.

“If we want to find the recipe for the formation of planets, asteroids are the best tracer, because they have remained small, they have not heated much and have kept the memory of the initial composition of the Solar System”, recalled Patrick Michel, member of the Hayabusa-2 mission at the Côte d’Azur Observatory, in The world, November 16, 2019. Hence the importance of Ryugu, the fourth object to donate its body to science, after the Moon, comet 81P / Wild-2 and the asteroid Itokawa.

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One year after this sample return, two articles from Nature Astronomy published on December 20 deliver the results of the first analyzes. “It is more than moving to observe a material whose age of 4.5 billion years goes back to the beginning of the formation of the Solar System. And for the first time, our tools allow us to observe the collection in its entirety ”, appreciates Jean-Pierre Bibring, professor of astrophysics at Paris-Saclay and responsible for one of the instruments, MicrOmega, which fitted the Mascot robot, dropped on the asteroid. “It’s a unique opportunity to observe this primitive material. We are very happy to have been invited to participate in these preliminary analyzes by the Japanese ”, also considers his colleague Cédric Pilorget, at the Institute of Space Astrophysics (IAS).

One of the darkest bodies in the Solar System

From the end of December 2020, a few days after recovery, analyzes began in a special Japanese laboratory, ensuring the protection of the Ryugu component material in vacuum or nitrogen enclosures to avoid contamination and degradation. The first article describes microscopic weighings and measurements of grains of different sizes. The second, informed by the observations of the IAS instrument, MicrOmega, delivers the first information on the composition of these grains.

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