Researchers use muon beams to analyze the elemental composition of samples from the asteroid Ryugu

(left) A muon X-ray created after a muon was captured by irradiated material and (right) a sample of the asteroid Ryugu. Credit: (left image) muon analysis team, (right image) JAXA

Stone samples brought back to Earth by the asteroid Ryugu had their elemental composition analyzed using an artificially generated muon beam from the particle accelerator in J-PARC. The researchers discovered a number of important elements needed to support life, including carbon, nitrogen and oxygen, but they also found that the abundance of oxygen compared to silicon in the asteroid Ryugu was different from any meteorites that have been 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 a mission to bring back samples from asteroid Ryugu, a C-type asteroid that researchers believed was rich in carbon. After successfully landing on Ryugu and collecting samples, Hayabusa 2 returned to Earth in December 2020 with samples intact.

Since 2021, researchers have conducted the first analyzes of the samples, led by Professor Shogo Tachibana of the University of Tokyo. Divided into different teams, the researchers studied the samples in different ways, including the shapes of the stone, the distribution of the elements and the mineral composition.

In this study, led by Professor Tomoki Nakamura of Tohoku University, 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, 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 accelerator at J-PARC.

They applied the method of elemental analysis using negative muons to the stones of the asteroid Ryugu, managing to determine their elemental compositions in a non-destructive way.

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

The bespoke experiment setup was developed to prevent samples from being contaminated by the Earth’s atmosphere. The interior is filled with helium gas and the chamber is lined with pure copper to minimize background noise. Credit: muon analysis team

This was important, because if the asteroids in the solar system had been built at the beginning of the solar system’s formation, they would still have hidden information about the average elemental composition at that time, and therefore of the entire solar system.

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. So, 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 who wanted to study them, they needed 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 emitting a quantum beam, or specifically a negative muon beam, produced by one of the world’s largest high-energy particle accelerators J-PARC in Ibaraki prefecture, in Japan, to identify the chemical elements of sensitive samples without breaking them.

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

Spectral comparison of muon X-rays of the sample of the asteroid Ryugu and of the chondrite CI Orgueil. Credit: muon analysis team

Takahashi and Nagasawa then applied statistical analysis techniques in X-ray astronomy and particle physics experiments to analyze the characteristic X-rays of muons.

Muons are one of the building blocks of the universe. Their ability to penetrate deeper into materials than X-rays makes them ideal in material analysis. When a negative muon is captured by the irradiated sample, a muon atom is formed. The muon X-rays emitted by the new muon atoms have a high energy and therefore can be detected with high sensitivity. This method was used to analyze Ryugu samples.

But there was another challenge. To prevent the samples from becoming 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 by fitting the sample into 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 the J-PARC and the researchers performed their X-ray analysis of the muon, which produced an energy spectrum. In it, they found the elements necessary to produce life, carbon, nitrogen and oxygen, but they also found that the sample had a similar composition to that of carbonaceous chondrite (chondrite CI) asteroids, which are often referred to as the standard for solid substances in the solar system. This showed that the Ryugu stones were some of the first stones to have formed in our solar system.

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

Comparison of the elemental composition of the sample of the asteroid Ryugu and of the chondrite CI Orgueil (K. Lodders, The Astrophysical Journal, 591, 1220-1247, 2003). The oxygen radiograph shows that the oxygen abundance of the Ryugu sample compared to the silicon was lower than the CI chondrite. Credit: muon analysis team

However, although similar in composition to CI chondrites, the oxygen abundance of the Ryugu sample relative to silicon was about 25% less than that of CI chondrite. The researchers say this could indicate that the abundance of oxygen in excess of silicon in CI chondrites could come from contamination after they enter Earth’s atmosphere. Ryugu’s stones could set a new standard for matter in the solar system.


Asteroid Ryugu dust grains oldest in our solar system


More information:
T. Nakamura, Formation and Evolution of the Ryugu Carbon Asteroid: Direct Evidence from Returned Samples, science (2022). DOI: 10.1126 / science.abn8671. www.science.org/doi/10.1126/science.abn8671

Provided by the Kavli Institute for Universe Physics and Mathematics

Citation: Researchers use muon beams to analyze the elemental composition of Ryugu asteroid samples (2022, September 22) recovered on September 22, 2022 from https://phys.org/news/2022-09-muons-elemental-composition -asteroid-ryugu .html

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