First look at Japanese Hayabusa2 asteroid sample indicates Ryugu is similar to ...
First look at Japanese Hayabusa2 asteroid sample indicates Ryugu is similar to Earth's rarest meteorites
ABC Science
/ By Genelle WeulePosted 6h ago6 hours ago, updated 4h ago4 hours ago
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Hayabusa2 fired an "impactor" into the Ryugu asteroid to stir up material not previously exposed to the atmosphere.
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Just over a year ago, a space capsule carrying a very special cargo streaked across the sky and touched down in the South Australian outback.
Key points:
- The Japanese Hayabusa2 mission is the first to bring a sample of dust and pebbles back to Earth from a carbon-rich asteroid
- The sample indicates Ryugu is very similar to the rarest type of meteorites that have fallen to Earth
- These meteorites contain elements similar to those found in the Sun
Sealed in a canister were samples of dust and pebbles blasted off Ryugu, a lumpy asteroid, by the Japanese Hayabusa2 mission.
When the team from the Japan Aerospace Exploration Agency (JAXA) first opened the canister they were excited to find they'd snapped up a good sample.
And when they got the canister back to their lab in Japan they were even more surprised.
"There was some feeling among us that we should get one gram of sample from Ryugu," said Masaki Fujimoto, who led the team that retrieved the capsule from the Woomera Rocket Range.
Inside was almost 5 grams of dust and rocks.
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Professor Masaki Fujimoto at Woomera in December 2020.(ABC News: Sarah Mullins)The first analysis of the physical properties and the composition of the material retrieved from the asteroid is revealed today in two papers in the journal Nature Astronomy.
It turns out Ryugu is a very rare type of asteroid with a mix of elements seen in less than a handful of meteorites that have been found on Earth.
"It's not just rare, it's a very precious sample," Professor Fujimoto said.
"It will tell us about the very early history of the Solar System, and the process that made Earth habitable."
First samples from a carbon-rich asteroid
162173 Ryugu is a small asteroid that sits between Earth and Mars.
Earlier observations of the diamond-shaped rock suggested it was a C-type asteroid packed full of carbon.
C-type asteroids are thought to have seeded early Earth with water and organic material.
While we've brought space rocks back from the Moon, a comet and a stony – or S-type – asteroid known as Itokawa, Hayabusa2 is the first mission to return with samples of a C-type asteroid.
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Image from 40 km above shows Ryugu's shape and boulders on its surface.(Supplied: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, Aizu University, AIST)C-type asteroids are the most common type in our solar system.
However, meteorites from these asteroids — known as carbonaceous chondrites — are so fragile they rarely make it through Earth's atmosphere intact.
That was why the sample return mission to Ryugu was so important, Professor Fujimoto said.
"Only a sample return mission can tell you what it is like in space."
Dark dust similar to exceptionally rare meteorite
The Hayabusa2 spacecraft scooped up samples from two sites on the asteroid in 2019.
"If you look at it with your eye it's nothing, but scientific instruments can tell us a lot," Professor Fujimoto said.
One of the first things the scientists noted was the sample was very dark – only reflecting about 2 per cent of the light that hit it, said Toru Yada from JAXA, who led one of the studies.
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The sample taken from two locations on Ryugu were a mix of dark-coloured dust and pebbles.(Supplied: Yada et al, Nature Astronomy)"[The sample] is comparable to what we observed with Hayabusa2, which means … it is representative of the whole Ryugu surface," Dr Yada said.
Measurements of the size and shape of some single grains of dirt under a microscope indicated the particles were very porous.
And infrared scans by Dr Yada's team and another team led by Cedric Pilorget at the University of Paris-Saclay confirmed the sample was rich in hydrated minerals and clays, and carbon.
"Hayabusa previously did remote sensing of Ryugu so we had some feeling there should be hydrated minerals in there and also organics," Dr Yada said.
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The samples confirmed observations taken by the Hayabusa2 spacecraft.(Supplied: JAXA)But there was also something very unusual about the sample – unlike other kinds of carbonaceous chondrites it had a uniformly fine texture and didn't contain any small blobs of melted minerals called chondrules.
That suggests Ryugu is the parent body of an exceptionally rare type of meteorite known as a CI chondrite, said Trevor Ireland, a planetary scientist and study co-author at the University of Queensland.
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Professor Trevor Ireland, a planetary scientist at the University of Queensland, observed the retrieval of the Hyabusa2 sample at Woomera in 2020.(Supplied: Trevor Ireland)"So the first C-type object we go to is a CI chondrite and that is particularly strange in terms of survival statistics," he said.
We've only seen about five of these types of meteorites fall to Earth.
"We don't see these meteorites all that often because they just don't survive," Professor Ireland said.
"The material brought back by the missionhas lower density than any meteorite that has ever been recovered.
"Even if it did come down to Earth, as soon as it rained it would be gone, it would dissolve into a little puddle of mud," he said.
'Priceless' sample of the Solar System
Not only are CI chondrites rare, they are very special because their chemical composition is similar to the Sun, said Phil Bland, a planetary scientist at Curtin University not involved in the studies.
"Imagine if you could take all of the gas away from the Sun and were just left with a vestige of other elements … you're left with a CI chondrite."
That means 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 [a pristine sample of this material] before and that makes this stuff priceless."
"It's a perfect window into the building blocks of the Solar System."
The results in the first two papers are just the initial description of what's in the sample, with more detailed studies yet to come, said Professor Fujimoto and Dr Yada.
"Even though we are limited to non-destructive methods we've still got these nice results really proving the high potential of the Ryugu samples," Professor Fujimoto said.
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Follow up studies using other techniques will tease out more information and compare the sample to the handful of CI meteorites that have fallen to Earth.
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 be going further," Dr Yada said.
In the future, the sample will also be compared to a sample from Bennu, another C-type asteroid between Earth and Mars, which is due to be brought to Earth by NASA's OSIRIS-Rex mission in 2023.
Bennu is a great follow-up mission in terms of "what else is there?" said Professor Ireland, who is also involved with the NASA mission.
"The question will be is it the same or is it going to be a different kind of body?"
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