Rock samples returned to Earth from asteroid Ryugu have their elemental composition analyzed using an artificially generated muon beam from the particle accelerator in J-PARC. Researchers found a number of key elements needed to sustain life, including carbon, nitrogen and oxygen, but also found that the amount of oxygen relative to silicon in asteroid Ryugu was different from any 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 a mission to return samples of asteroid Ryugu, a type C 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 been conducting the first analyzes of the samples, led by Professor Shogo Tachibana of the University of Tokyo. Split into several teams, researchers studied the samples in a variety of ways, including rock 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 basic analysis methods using negative muons, elementary particles produced by the accelerator at J-PARC.
They applied the elemental analysis method using negative muons on rocks from the asteroid Ryugu, and managed to determine their elemental compositions non-destructively.
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 withhold information about the average elementary composition at that time, and thus of the entire solar system.
Analysis of meteorites that have fallen to Earth has been conducted in the past, but it is possible that these samples were contaminated by Earth’s atmosphere. So until Hayabusa 2, no one knew for sure what an asteroid’s chemical makeup was.
But the researchers faced a challenge. Due to the limited number of samples and the large number of other researchers who wanted to study them, they had to find a way to conduct their analyzes without damaging them so that the samples could be passed on to other groups.
The team had developed a new method in which 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, was fired to extract the chemical elements of sensitive samples without using them. to break.
Takahashi and Nagasawa then applied statistical analysis techniques in X-ray astronomy and particle physics experiments to analyze muon-characteristic X-rays.
Muons are one of the elementary particles in the universe. Their ability to penetrate materials deeper than X-rays makes 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 the new muonic atoms have a high energy and thus can be detected with a high sensitivity. This method was used to analyze the Ryugu samples.
But there was another challenge. To prevent the samples from being contaminated by Earth’s atmosphere, the researchers had to keep the samples out of contact with oxygen and water in the air. So they had to develop an experimental setup, encasing the sample in a chamber of helium gas. The inner walls of the chamber were lined with pure copper to minimize background noise when analyzing the samples.
In June 2021, 0.1 gram of Ryugu asteroid was introduced into J-PARC and the researchers performed their muon X-ray analysis, which produced an energy spectrum. 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 carbonaceous chondrite (CI-chondrite) asteroids, often referred to as the standard for solids in the solar system. This showed that the Ryugu stones were some of the earliest stones formed in our solar system.
Although the composition is similar to CI chondrites, the oxygen abundance of the Ryugu sample relative to silicon was about 25 percent less than that of the CI chondrite. The researchers say this could indicate that the excess oxygen over silicon in CI chondrites could have come from contamination after they entered Earth’s atmosphere. Ryugu rocks could set a new standard for matter in the solar system.
T. Nakamura, Formation and Evolution of 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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