Japan probe finds scars of micrometeoroid bombardment on asteroid Ryugu

Analysis of asteroid Ryugu samples hints at its surface property changes over time, some most likely due to collisions with micrometeoroids. 

A micrometeoroid refers to a particle tinier than a grain of sand. As per NASA, millions of micrometeoroids strike Earth's atmosphere every day.

However, the majority of them never make it to the Earth's surface as they get vaporized upon entering the atmosphere.

The Japanese Space Agency's Hayabusa2 spacecraft traveled far, arriving at the asteroid Ryugu in June 2018. In December 2020, the spacecraft returned the asteroid Ryugu samples to Earth and resumed its voyage to other asteroids.

Hokkaido University researchers discovered signs of the "magnetic and physical bombardment environment of interplanetary space" in the analyzed samples. 

Sample analysis using electron holography

Direct sample analysis offers several advantages over robotic explorers conducting it from the surface of an asteroid or planet and then beaming back the data.

It provides a window into understanding how the surface of a celestial body has changed due to its constant exposure to the harsh deep space environment. 

The scientists conducted their analysis using electron holography, a technique in which electron waves infiltrate materials. This method has the potential to uncover key details about the sample's structure and magnetic and electric properties. 

They observed indications of space weathering due to solar wind and micrometeoroid impacts over time. The solar wind consists of highly charged particles released by our star, the Sun.

"The signatures of space weathering we have detected directly will give us a better understanding of some of the phenomena occurring in the Solar System," said Professor Yuki Kimura from the university who led the research study. 

Alteration of mineral grains

Moreover, the asteroid sample analysis revealed the alteration of tiny mineral grains called framboids. 

These minerals are made up of magnetite, a type of iron oxide. The analysis showed that framboids had lost their magnetic characteristics, suggesting impacts with high-velocity micrometeoroids.

These tiny entities most likely measured between 2 and 20 micrometers in diameter. 

"The framboids were surrounded by thousands of metallic iron nanoparticles. Future studies of these nanoparticles will hopefully reveal insights into the magnetic field that the asteroid has experienced over long periods of time," the press release mentioned. 

Hayabusa2 spacecraft on its way to explore other asteroids

Furthermore, these findings provide valuable clues about the early solar system and can help experts better understand the magnetic field dynamics during its formation.

Experts believe that when planets developed in the early solar system, the intensity of the magnetic field was reduced.

Scientists can learn about the parameters of the magnetic field during the early phases of the solar system's history by analyzing the residual magnetization found on asteroids. 

Kimura adds in the press release: "In future work, our results could also help to reveal the relative ages of surfaces on airless bodies and assist in the accurate interpretation of remote sensing data obtained from these bodies."

Kimura mentions that the findings hold practical implications as well. 

Specifically, this study's findings might help estimate the level of deterioration that spacecraft—both robotic and manned—may endure as a result of high-velocity encounters with space dust.

Meanwhile, the Hayabusa2 spacecraft is on its way to explore two other asteroids in 2029 and 2031.

The findings have been published in the journal Nature Communications.

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