First look at the Ryugu asteroid sample delivered by the Hayabusa-2 mission

The samples confirmed the observations made by the Hayabusa-2 spacecraft.  (Supplied: JAXA)
The samples confirmed the observations made by the Hayabusa-2 spacecraft. (Supplied: JAXA)

Just over a year ago, a space capsule carrying a special cargo flew across the sky and landed in the South Australian outback.

Dust and rock samples collected by the Japanese mission were sealed in the container. Hayabusa-2 from an asteroid Ryugu… When a team from the Japan Aerospace Exploration Agency (JAXA) first opened container, they were delighted to have received a good sample. And when they brought the container to their laboratory in Japan, they were even more surprised. “We had the feeling that we should get one gram of a sample from Ryugu,” said Masaki Fujimoto, who led the team that retrieved the capsule from the Woomera rocket range. Inside, there were almost 5 grams of dust and stones.

Professor Masaki Fujimoto in Woomera, December 2020 (ABC News: Sarah Mullins)

First analysis physical properties and composition The material extracted from the asteroid was published on Tuesday December 21st in two articles in the journal Nature Astronomy. It turns out that Ryugu is a very rare type of asteroid with a mixture of elements found in less than a handful of meteorites found on Earth. “This is not just a rarity, it is a very valuable specimen,” said Professor Fujimoto. “This will tell us about the earliest history of the solar system and the process that made the earth habitable.”

First samples of carbon-rich asteroid

(162173) Ryugu is a small asteroid located between Earth and Mars. Earlier observations of the diamond-shaped rock showed it to be a C-type asteroid composed primarily of carbon. C-type asteroids are believed to have seeded early Earth water and organic material. Although we brought space stones from the moon, from comets and from an S-type rock asteroid known as ItokawaHayabusa 2 is the first mission to return with samples of a C-type asteroid.

The image from an altitude of 40 km shows the shape of Ryugu and the boulders on its surface. (Supplied: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, Aizu University, AIST)

Type C asteroids are the most common type in our solar system. However, the meteorites of these asteroids, known as carbonaceous chondrites, are so fragile that they rarely pass through Earth’s atmosphere intact. This is why the mission to recover samples from Ryugu was so important, said Professor Fujimoto.

Dark dust similar to an exceptionally rare meteorite

In 2019, the Hayabusa 2 spacecraft collected samples from two locations on the asteroid. Samples have landed on Earth in December last year. “If you just look at it with your eyes, you won’t see anything special, but scientific instruments can tell us a lot,” said Professor Fujimoto. According to Toru Yada of JAXA, who led one of the studies, one of the first things the scientists noted was that the sample was very dark – only reflecting about 2 percent of the light falling on it.

Samples taken from two locations on Ryugu were a mixture of dark dust and rocks. (Supplied: Yada et al, Nature Astronomy)

“[Образец] comparable to what we observed from Hayabusa-2, which means … that it is representative of the entire surface of Ryugu, ”said Yada. Measurements of the size and shape of individual dust grains under a microscope showed that the particles were very porous. And an infrared scan by Dr. Yada’s team and another team led by Cedric Pilorget of the University of Paris-Saclay confirmed that the sample is rich in hydrated minerals, clays and carbon. “Hayabusa previously remote sensing Ryugu, so we had a feeling that there must be hydrated minerals as well as organic matter, ”said Dr. Yada.

But there was also something very unusual about this sample – unlike other types of carbonaceous chondrites, it had a uniform fine texture and did not contain small droplets of molten minerals called chondrules. This suggests that Ryugu is the parent body of an exceptionally rare type of meteorite known as chondrite CIsaid Trevor Ireland, a planetary scientist and research co-author at the University of Queensland.

Professor Trevor Ireland, a planetary scientist at the University of Queensland, oversaw the extraction of a Hayabusa-2 sample at Woomer in 2020. (Supplied: Trevor Ireland)

We found only five of these meteorites that fell to Earth. “We don’t see these meteorites that often because they just don’t survive,” said Professor Ireland. “The material delivered by the mission has a lower density than any meteorite that has ever been detected. Even if he really reached the Earth, he would dissolve into a small puddle of mud as soon as it started to rain, ”the professor said.

Priceless specimen from the solar system

CI chondrites are not only rare, they are very special because their chemical composition is similar to the sun, said Phil Bland, a planetary scientist at Curtin University in Western Australia who was not involved in the research. “Imagine if you could remove all the gas from the Sun and only traces of other elements remained … you would have CI chondrite.” This means that CI chondrites are very important to scientists because they provide a snapshot of the composition of the solar system when it first formed. “We’ve never had [нетронутого образца этого материала]and that makes this material invaluable. “

According to Prof. Fujimoto and Dr. Yada, the results of the first two articles are just an initial description of what is in the sample, and more detailed research is still to come. “Despite the fact that we are limited to non-destructive methods, we still got excellent results that really prove the high potential of the Ryugu samples,” said Professor Fujimoto.

Subsequent studies using other methods will provide more information and compare the sample to the handful of CI meteorites that hit Earth. A more detailed analysis of the sample will also tell us more about how Ryugu and the solar system evolved. “Our exciting journey has just begun and we will move on,” said Dr. Yada.

In the future, this sample will also be compared with a sample with Bennu, another C-type asteroid between Earth and Mars, to be delivered to Earth by NASA OSIRIS-Rex in 2023. “Bennu is a great continuation of the mission in terms of ‘what else is there?’” Said Professor Ireland, who is also involved with the NASA mission. “The question is, will it be the same or will it be a different type?”

Other articles on this topic:

Impactors: how and why they shoot at celestial bodies

Six years of Hayabusa-2

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