The Hayabusa2 target Ryugu was once part of a much larger asteroid

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Everyone is currently focused on his revenge for the dinosaurs by crashing the DART spacecraft into an asteroid, but that wasn’t our first salvo against the space rock threat. It’s been just over three years since Japan’s Hayabusa 2 probe fired multiple metal slugs at asteroid Ryugu to collect samples. It wasn’t just a matter of justice for the dinos, though. Hayabusa2 elements have been on Earth since late 2020, and new research reveals how Ryugu has changed over its lifetime, including a catastrophic impact that turned it into the small-ish rock it is today.

The Japan Aerospace Exploration Agency (JAXA) shared its precious 5.4 grams of Ryugu among six different teams around the world. One of the most interesting discoveries is how and where Ryugu was formed. Based on the residual magnetization in the samples, scientists determined that Ryugu formed in the primordial solar nebula, which existed before the planets formed and has since condensed into the planets, moons, asteroids and comets we see today. That means, by some measures, parts of Ryugu are older than the Solar System.

Ryugu formed when the nebular gas was still very dense, blocking sunlight and dropping temperatures to -200 °C (-328 °F). This original body collected large amounts of water and carbon dioxide ice and was probably about 62 miles (100 kilometers) in diameter. Water and carbon dioxide react in the parent body to form hydrous silicate and carbonate minerals, which make up most of the samples obtained by Hayabusa2. Even some liquid water was still trapped inside the crystals in the sample.

The research suggests that the original Ryugu collided with a smaller object, about a tenth of its size, a billion years ago. This event exploded the main body into pieces, and part of it reformed as the sub-kilometer asteroid we know today. Scientists report that today’s Ryugu is a mixture of internal and external materials from the parent’s body. It is believed that water-bearing asteroids such as Ryugu, which formed outside Jupiter’s orbit and later pulsated, may have played a role in the early formation of planets in the Solar System.

We’ve obviously learned a lot already from a few villages of Ryugu, and there’s more to come. NASA’s OSIRIS-REx mission collected several kilograms of material from Bennu and is now on its way to Earth. It is expected to land in September 2023, about a year from now.

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