An analysis of samples from asteroid Ryugu offers insights into its space environment

Magnetite particles cut from an asteroid Ryugu's sample
An article published in the journal “Nature Communications” reports the results of tests conducted on samples from the asteroid Ryugu brought back to Earth by the Japanese space agency JAXA’s Hayabusa 2 space probe. A team of researchers led by Professor Yuki Kimura of Hokkaido University found traces of the effects probably caused by the bombardment of micrometeorites.

In particular, the technique called electron holography made it possible to discover that the tiny grains called framboids, composed of magnetite, completely lost the magnetic properties they normally have. According to Professor Kimura, this type of study can also be useful for estimating the degradation caused by interplanetary dust on spacecraft.

The image (Courtesy Yuki Kimura, et al. Nature Communications) shows magnetite particles cut from an asteroid Ryugu’s sample. (A) shows a bright field transmission electron microscope image while (B) shows an image of the magnetic flux distribution obtained by electron holography.

In December 2020, the Hayabusa 2 Japanese space probe parachuted to Earth the container with samples taken over two years earlier on asteroid Ryugu. The procedures used in handling those samples have as their priority the prevention of their contamination, therefore each examination requires a long time. Now a study showed the internal structure of some samples and the effects of space weathering on them.

To obtain these results, the group of researchers from thirteen Japanese institutions led by Professor Yuki Kimura used the sophisticated technique called electron holography. It’s a technique that allows to create 3D images using electrons instead of light to scan microscopic objects. In this case, these are samples from asteroid Ryugu into which electron beams penetrated, which also made it possible to detect their electromagnetic characteristics.

Framboids are tiny grains of the iron oxide called magnetite. The name isn’t accidental since normally this material has magnetic properties but the framboids arrived from Ryugu lost it. According to the researchers, that’s due to the bombardment of micrometeorites, microscopic particles with a diameter between 2 and 20 micrometers. The framboids were surrounded by thousands of iron nanoparticles, and examining them could offer insight into the magnetic field experienced by Ryugu for a long time.

Space weathering can only be studied with precision in samples such as the ones collected directly on asteroids. That’s because meteorites that fall to Earth are altered by friction as they descend into the atmosphere.

This study may pave the way for new discoveries about the magnetic field experienced by asteroid Ryugu for long periods of time. This would provide new information useful to the history of asteroids and the solar system in general. This is an important reconstruction also when thinking about the complex molecules, up to uracil, found in the samples. Professor Kimura thinks that this type of study could also help estimate the degradation caused by space dust affecting spacecraft, including crewed ones. In essence, the electron holography technique could have important developments.

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