By examining samples brought back from the asteroid explorer Hayabusa2, an international team of scientists including Dr. Ashley King and Prof. Sara Russell of the Natural History Museum, examining the mineralogy of the carbonaceous asteroid and revealing its early history.
The pattern return
Hayabusa2 is an asteroid sample return mission operated by Japan’s national space agency JAXA, and is the fifth mission ever to collect samples from a known object in our solar system. In December 2020, Hayabusa2 returned with a capsule containing approximately 5g of sample from the asteroid Ryugu. The team was able to study this sample in incredible detail, almost atom by atom, in labs here on Earth, including the museum.
dr Ashley King of Earth Sciences at the museum obtained a combination of materials from the sample, including powder, flat polished surfaces and a small chip approximately 3mm in size. He says: “By examining the minerals in small fragments of the returned samples, we were able to reconstruct the 4.6 billion year history of the asteroid Ryugu. We now know that it records chemical reactions between water and rock in the cold, outer regions of the solar system. Asteroids like Ryugu are the building blocks of the solar system and could help us understand the origin of water on Earth.’
A key finding of this study is the confirmation that Ryugu is a carbonaceous chondrite. Although long suspected by the planetary scientific community, only exemplary return missions such as Hayabusa2 can provide complete confidence. This confirmation is the basis on which all subsequent investigations can now be built.
Carbonaceous chondrites are primitive building blocks of our solar system and may provide answers to some of humanity’s biggest questions, such as how the planets formed. Hayabusa2 is the first mission to bring back samples from a carbonaceous asteroid.
The team found that Ryugu’s mother body formed very early – within the first few million years of the solar system – and formed between C02 and snow lines, the point where it’s cold enough for ice to form. Today this would fall around the main asteroid belt between Mars and Jupiter.
Based on the detection of the magnetic field in the samples examined, it is likely that Ryugu’s mother body was born of CO2 ice and rock particles in the darkness of the nebula gas, far from the sun where sunlight cannot reach. However, there was also a small amount of particles formed at high temperatures. These had migrated into the outer solar system from near the sun, indicating a strong mixing of materials in the inner and outer solar systems at the time of Ryugu’s birth. Chemically, Ryugu has a very primitive structure, similar to that of the sun, suggesting it evolved from the same primordial cloud.
The asteroid’s parent body was then struck by a violent collision that shattered it into smaller pieces. Some of these pieces then merged together to create a “rubble pile” that is the ryugu we know today.
Prof Sara Russell, Merit Researcher in Cosmic Mineralogy and Planetary Sciences at the Museum, says: “It was so exciting to be involved in such an ambitious mission to an asteroid and back and we are thrilled to see that the rocks returned are tight Relatives of are some of the precious space rocks that make up our collection of meteorites in the Natural History Museum.’
The paper Formation and Evolution of Carbonaceous Asteroid Ryugu: Direct Evidence from Backsampling under the supervision of Prof. Tomoki Nakamura, Tohoku University, was published in Science on Thursday 22 September at 7pm BST.
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