Stone samples brought back to Earth from the asteroid Ryugu have had their elemental composition analyzed using a beam of muons artificially generated by the J-PARC particle accelerator. The researchers discovered a number of important elements needed to sustain life, including carbon, nitrogen and oxygen, but also found that the abundance of oxygen relative to silicon in asteroid Ryugu was different from all meteorites found on Earth, reports a new study in Science.
In 2014, the unmanned asteroid explorer Hayabusa 2 was launched into space by the Japan Aerospace Exploration Agency (JAXA) with the mission of bringing back samples of asteroid Ryugu, a C-type asteroid that researchers believed to be carbon-rich. After successfully landing on Ryugu and collecting samples, Hayabusa 2 returned to Earth in December 2020 with samples intact.
Since 2021, researchers have carried out the first analyzes of the samples, led by Professor Shogo Tachibana from the University of Tokyo. Divided into several teams, the researchers studied the samples in different ways, including stone shapes, elemental distribution and mineral composition.
In this study, led by Tohoku University Professor Tomoki Nakamura, Professor Tadayuki Takahashi and graduate student Shunsaku Nagasawa of the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), University of Tokyo, in collaboration with the High Energy Accelerator Research Organization (KEK) Institute for Materials Structure Science, Osaka University, Japan Atomic Energy Agency (JAEA), Kyoto University, International Christian University, Institute of Space and Astronautical Science (ISAS) and Tohoku University, applied elementary analysis methods using negative muons, elementary particles produced by the J-PARC accelerator.
They applied the elemental analysis method using negative muons to the stones of the asteroid Ryugu, successfully determining their elemental compositions non-destructively.
This was important, because if the asteroids in the solar system were built early in the formation of the solar system itself, they would still retain information about the average elemental composition at that time, and therefore about the entire system solar.
Analyzes of meteorites that have fallen to Earth have been carried out in the past, but it is possible that these samples have been contaminated by the Earth’s atmosphere. Thus, until Hayabusa 2, no one knew for sure what the chemical composition of an asteroid was.
But the researchers faced a challenge. Due to the limited amount of samples and the large number of other researchers wishing to study them, they had to find a way to perform their analyzes without damaging them so that the samples could be passed on to other groups.
The team had developed a new method, which involved firing a quantum beam, or more specifically a negative muon beam, produced by one of the world’s largest high-energy particle accelerators J-PARC in the prefecture of Ibaraki, Japan, to identify chemical elements in sensitive samples without breaking them.
Takahashi and Nagasawa then applied statistical analysis techniques in X-ray astronomy and particle physics experiments to analyze characteristic muon X-rays.
Muons are one of the elementary particles of the universe. Their ability to penetrate deeper into materials than X-rays make them ideal for materials analysis. When a negative muon is captured by the irradiated sample, a muonic atom is formed. The muonic X-rays emitted by new muonic atoms have high energy and can therefore be detected with high sensitivity. This method was used to analyze the samples from Ryugu.
But there was another challenge. In order to prevent the samples from being contaminated by the Earth’s atmosphere, the researchers had to keep the samples out of contact with oxygen and water in the air. Therefore, they had to develop an experimental setup, enclosing the sample in a helium gas chamber. The interior walls of the chamber were lined with pure copper to minimize background noise during sample analysis.
In June 2021, 0.1 grams of asteroid Ryugu was introduced into J-PARC, and the researchers performed their X-ray analysis of the muons, which produced an energy spectrum. They found there the elements necessary for the production of life, carbon, nitrogen and oxygen, but they also discovered that the sample had a composition similar to that of carbonaceous chondrite (CI chondrite) asteroids. , often called the standard for solid substances. in the solar system. This showed that the Ryugu Stones were among the first stones to form in our solar system.
However, although similar in composition to the CI chondrites, the oxygen abundance of the Ryugu sample relative to silicon was about 25% lower than that of the CI chondrite. The researchers say this could indicate that the excess oxygen relative to silicon in the CI chondrites could come from contamination after they entered the Earth’s atmosphere. The Ryugu stones could set a new standard for matter in the solar system.
Dust grains from the asteroid Ryugu older than our solar system
T. Nakamura, Formation and Evolution of the Carbonaceous Asteroid Ryugu: Direct Evidence from Returned Samples, Science (2022). DOI: 10.1126/science.abn8671. www.science.org/doi/10.1126/science.abn8671
Provided by Kavli Institute for the Physics and Mathematics of the Universe
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