by An analysis of samples collected from asteroid Ryugu revealed its origin and birthplace.
The findings show that although Ryugu now classified as a near-Earth object, its journey inward solar system it started hundreds of millions of miles away and billions of years ago.
Asteroids such as Ryugu are composed of intact material left over from the formation of the solar system 4.5 billion years ago. This means they contain information about the chemical state of the early solar system that could lead to a better understanding of how our cosmic backyard has evolved.
Related: The pieces of asteroid Ryugu are among the most “primordial” materials ever examined
Ryugu — which is now 60,000 miles (97,000 km) from Earthvisited by the Japan Aerospace Exploration Agency (JAXA) Hayabusa2 spaceship in 2019.
In 2020, Hayabusa2 collected and returned samples which have now been analyzed by teams of scientists around the world. Different teams used dozens of research techniques to analyze the properties of the samples, such as rock shape, elemental distribution and mineral composition.
A team, from the US Department of Energy’s Argonne National Laboratory, used an X-ray technique called Mössbauer spectroscopy to look for microscopic changes in the chemistry of the Ryugu samples by probing the fragments of each particle.
Their results were amazing.
“There is enough evidence that Ryugu started in the outer solar system,” said Esen Ercan Alp, a senior physicist in the X-ray Science division at Argonne National Lab who led the research. statement. ”Asteroids in the outer regions of the solar system will have different characteristics than those closer to the sun.”
One piece of evidence that Ryugu comes from the edges of the solar system is that the grains that make up the asteroid are finer than they would be if they had formed at the higher temperatures found closer to sun.
In addition, the fragments are porous, indicating that they once held water and ice.
Carbon dioxide and water would exist in solid form about three to four times distance from the sun to Earthmeaning Ryugu’s parent body was at least that far away, possibly even beyond its orbit Zeus.
Unlike asteroid fragments that reach Earth’s surface after passing through our planet’s oxygen-rich atmosphere, Ryugu’s pieces were delivered to Earth in vacuum-sealed containers, so they were never exposed to oxygen. Therefore, the team could assess the oxidation that the Ryugu samples had experienced.
Their analysis revealed that the chemical composition of the Ryugu samples is similar to that of meteorites that have hit Earth, particularly a rare group called CI chondrites, of which there are only nine known samples on the planet.
Using spectroscopy, the researchers found another feature that distinguished the Ryugu samples: a large amount of pyrrhotite, an iron sulfide missing from the dozen other meteorite samples they examined.
Ryugu is thought to have formed when a larger body was struck by another space rock, and like the fingerprint of ice, a large amount of pyrrhotite helps to constrain where Ryugu’s parent asteroid was when that collision occurred.
“Our results and those from other groups show that these asteroid samples differ from meteorites, particularly because meteorites have undergone fiery atmospheric entry, weathering, and especially oxidation on Earth,” said Michael Hu, an Argonne physicist and member of the research team, the announcement states. “This is exciting because it’s a completely different kind of sample, from going out into the solar system.”
Along with research by hundreds of other scientists at 11 institutions, the results from Argonne reveal billions of years of Ryugu history.
Writing Ryugu’s biography
So far, research indicates that Ryugu’s parent body formed about 2 million years after the solar system. Although this parent body was originally composed of many different materials—including water and carbon dioxide ice—over the next 3 million years, that ice melted and left a hydrated interior and a relatively dry surface.
A billion years or so later, the parent body experienced the cosmic collision that ejected fragments that coalesced to become the asteroid we call Ryugu.
The lack of shockable material in the fragments, which are created by asteroid impacts or other impacts, indicates that Ryugu formed away from the impact and then migrated toward the inner solar system, the researchers said.
“For planetary scientists, this is first-rate information coming directly from the solar system, and as such is invaluable,” Alp said.
The Argonne team’s results are part of a paper published in the journal Science September 22 containing the work of several groups that analyzed Ryugu samples. The Argonne team will publish their results separately at a later date.
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