Asteroids are many things – dinosaur killers, archives of the early days of the solar system, targets for planetary defense – but they don’t have to be water worlds. TRUE?
At least not these days. But in the early days of the Solar System’s formation, Ryugu, the diamond-shaped target of the Japan Aerospace Exploration Agency (JAXA), Hayabusa2 task – inside there is a small ocean.
Before it became the asteroid today, high-precision isotope analysis shows it was part of a larger, older parent before it was disintegrated in a collision. But even more surprising is that in that tiny ocean, some dry silicates from the original parent asteroid managed to survive unchanged. A new article from one of Hayabusa’s Curatorial Teams published this month Nature Astronomy He understands what Ryugu’s parent has shown about the structure and the asteroids of the very early Solar System.
WHAT’S UP – In December 2020, Hayabusa2 returned just over five grams of Ryugu after a six-year mission. Because the samples were relatively limited in number of small particles, each was labeled with its own name and number. In this case, the team’s analysis relied on just one of these particles, C0009.
talk to Oppositeisotope cosmochemist Ming Chang Liu From UCLA, he explains that C0009 is particularly interesting because it “is distinguished by having a small amount of anhydrous silicates”—that is, it contains oxygen-enriched minerals that are unaffected by water in the middle of a sample that is strongly modified by H2O.
Ryugu’s structure has been significantly altered by the liquid water inside. Although it formed deep within the cold outer Solar System, water and carbon dioxide ice combined with short-lived radioactive isotopes in the protolith that formed Ryugu’s parent. Liu notes that as these radioactive rocks heat the ice around them, they will “start floating within the main body”—and over time converts the silicates and pyroxine that made up Ryugu’s predecessor into water-bearing phyllosilicates.
The remaining anhydrous silicates give the team a clue as to what other material in the early Solar System might have looked like before it crashed into Ryugu’s small ocean. And the materials are similar to the earliest materials formed in the Sun’s photosphere. Oxygen isotopes in the sample the team worked with show that the asteroid contains amoeboid olivine and magnesium-rich chrondules directly combined with the solar nebula.
Motoo Ito, cosmochemist and member of the larger Phase 2 team at the Japan Sea-Earth Science Technology Agency, with Liu et al. A study of the pristine particles of RyuguThis shows how CI meteorites on Earth have been altered by our own much more volatile environment.
talk to OppositeIto notes that even though knowing the chemical composition “doesn’t tell us where the main body formed,” it still allows us to “construct a kind of Ryugu history, how it formed in the outer solar system.”
WHY IMPORTANT — This work stems from the efforts of the larger Phase 2 Curatorial Team. After Hayabusa2 passed by Earth to drop off its cargo, the five-gram sample it brought back was split between eight teams: six of them perform specific initial analyzes for chemical makeup, stony and sandy substances, volatiles, and solid and soluble organic matter. two other major international teams working to clarify the potential scientific impact of materials and samples.
In June, Liu and Ito’s larger team from Okayama University in western Japan published interpretations of the specimens. They found that Ryugu’s phyllosilicates were similar to those found in CI chondrites, a rare and very primitive type of meteorite mostly collected in Antarctica.
But they “could have been sitting there for decades, years, before we got them,” Liu notes. “Earth has a very reactive atmosphere, so CI chondrite materials will interact with the atmosphere.” By comparison, samples from Hayabusa2 are “probably the purest chondrite materials a human can get.”
The survival of these elements of Ryugu’s first stone is perhaps even more surprising in light of the work of some other teams. Stony Analysis Team published its first results this month ScienceIt also contained liquid water from Ryugu trapped inside a crystal. The liquid water in the sample is carbonated, as Ryugu takes up frozen carbon dioxide as well as water ice as it forms.
NEXT – Some of the context for Ryugu is already on its way to Earth. Last May, NASA OSIRIS-REx The spacecraft left the asteroid Bennu after collecting half a kilo of rock to begin its journey to Earth. This was after OSIRIS-REx unexpectedly pierced a 20-metre crater on Bennu’s side – a result of being held together much less tightly than anyone expected.
Like Ryugu, Bennu is a relatively intact carbonaceous asteroid, although it is a different type: B-type asteroids like Bennu appear slightly bluer than Ryugu and other C-types that appear reddish. But regardless of their color, finding similarly complex carbonaceous components in the sample “will tell us about the distribution of organic compounds in the solar system,” according to cosmochemist Ito.
While this study answers questions about Ryugu’s structure, it also raises questions about how Ryugu fits into the most primitive asteroids and meteorites schema. According to Liu, the team thinks that “these starting materials may be very similar,” despite different categories emerging over the years to encompass all the different chondrites found on Earth. We just want to be a little provocative, stir things up a bit, try to change the paradigm,” he added.
