The researchers used muon beams to analyze the elemental composition of the asteroid samples Ryugu

Newswise – The components of stones brought to Earth from the asteroid Ryugu were analyzed using a muon beam synthesized from the particle accelerator at J-PARC. Researchers have found a number of important elements needed to sustain life, including carbon, nitrogen and oxygen, but they also found that the abundance of oxygen relative to silicon in the Ryugu asteroid is different from all meteorites found on Earth, according to a new study in Sciences.

In 2014, the Japan Aerospace Exploration Agency (JAXA) launched the unmanned asteroid explorer Hayabusa 2 into space on a mission to return samples from the Ryugu asteroid, a type C asteroid that researchers believe is rich in carbon. After successfully landing on Ryugu and collecting samples, Hayabusa 2 returned to Earth in December 2020 with intact samples.

Since 2021, researchers have conducted the first analyzes of the samples, led by University of Tokyo professor Shogo Tachibana. Split into several teams, the researchers were studying the samples in different ways, including lithic shapes, elemental distribution, and mineral composition.

In this study, Tohoku University professor Tomoki Nakamura, Professor Tadayuki Takahashi and graduate student Shunsaku Nagasawa of the Kavli Institute for Physics and Mathematics of the Universe (Kavli IPMU), University of Tokyo, led in collaboration with the High Energy Acceleration Research Organization (KEK) Institute for Material Structure Science, and Osaka University. , the Japan Atomic Energy Agency (JAEA), Kyoto University, International Christian University, Institute of Astronautics and Astronautics (ISAS), and Tohoku University have applied elemental analysis methods using negative muons, the elementary particles produced by the accelerator at J-PARC. They applied the method of elemental analysis using negative muons to stones from the asteroid Ryugu, and succeeded in determining their elemental compositions in a non-destructive manner.

This was important, because if asteroids were built in the solar system at the beginning of the formation of the solar system itself, they would still obscure information about the average initial formation at that time, and therefore about the entire solar system.

Analysis of meteorites that have fallen to Earth has been carried out in the past, but it is likely that these samples were contaminated by the Earth’s atmosphere. Therefore, until Hayabusa 2, no one knew what the chemical composition of the asteroid was for sure.

But the researchers faced a challenge. Due to the limited number of samples and the large number of other researchers willing to study them, they needed to find a way to conduct their analyzes without destroying them so that the samples could be transferred to other groups.

The team developed a new method, which involved firing a quantum beam, or specifically a beam of negative muons, produced by one of the world’s largest high-energy particle accelerators J-PARC in Ibaraki Prefecture, Japan, to determine the chemical elements of sensitive samples without breaking them.

Then Takahashi and Nagasawa applied statistical analysis techniques in X-ray astronomy and particle physics experiments to analyze the muon property of X-rays.

Muons are one of the elementary particles in the universe. Its ability to penetrate materials deeper than X-rays makes it ideal for material analysis. When the negative muon is captured by the irradiated sample, a muon atom is formed (Fig. 1). The muon x-rays emitted by the new muon atoms have high energy, and therefore can be detected with high sensitivity. This method was used to analyze the Ryugu samples.

But there was another challenge. In order to prevent the samples from contaminating Earth’s atmosphere, the researchers needed to keep the samples away from contact with oxygen and water in the air. Therefore, they had to develop an experimental setup, placing the sample in a helium gas chamber (Fig. 2). The inner walls of the chamber were lined with pure copper to reduce background noise when analyzing samples.

In June 2021, 0.1 grams of asteroid Ryugu was brought to J-PARC, and researchers performed muon X-ray analysis, which produced an energy spectrum (Fig. 3). In it, they found the elements needed to produce life, carbon, nitrogen and oxygen, but they also found that the sample had a composition similar to that of the CI chondrite asteroids, which are often referred to as standard solids. in the solar system. This showed that the Ryugu stones were among the oldest stones that formed in our solar system.

However, while the composition of the Ryugu sample is similar in composition to that of the CI chondrite, the oxygen abundance of the Ryugu sample relative to silicon was about 25 percent lower than that of the CI chondrite (Fig. 4). The researchers say this may indicate that the excess abundance of oxygen relative to silicon in the CI chondrite could be due to pollution after it enters the Earth’s atmosphere. Ryugu stones could set a new standard for matter in the solar system.

The team’s results show the success of the muon X-ray method, and could be used to analyze samples from future space missions.

Details of this study have been published in Sciences On September 22.