We finally have the very first analysis of stardust recovered from asteroid Ryugu

It’s been over a year since the Hayabusa2 probe delivered its precious cargo of dust from an alien space rock, and we finally have a more detailed look at what constitutes asteroid Ryugu.

In two papers published today, international teams of scientists have revealed that, according to analyzes conducted by the probe while on the asteroid, Ryugu is very dark, very porous, and among the solar system’s materials. most primitive we have ever had access to. here on Earth.

While this is not unexpected, the results are very cool. Since the asteroid has remained more or less unchanged since the formation of the solar system 4.5 billion years ago, the sample is one of our best tools to date for understanding the makeup of dust. from which the internal objects of the solar system merged.

“The samples returned by Hayabusa2… appear to be some of the most essential materials available in our labs,” wrote one of the teams in their article. “The samples constitute a particularly valuable collection, which can help to revisit the paradigms of the origin and evolution of the solar system.”

Asteroid Ryugu, formerly known as 1999 JU3, is just the second asteroid from which a sample return mission has been conducted. The first was Itokawa, whose sample return mechanism failed, causing only a tiny amount of dust to finally reach Earth in 2010.

Ryugu is about a kilometer (0.62 mile) in diameter, with a ridge around its equator; it travels in an elliptical orbit that transports it just inside the Earth’s orbital path around the Sun, and then almost as far as the orbit of Mars. The mission to reach the asteroid, double-hit it, and then bring any collected dust back to Earth took a deeply impressive level of skill and planning.

But it worked, and 5.4 grams of precious asteroid dust was returned and duly analyzed, while Hayabusa2 set out on a series of rendezvous with other asteroids over the next several years.

Ryugu samples returned by the Hayabusa2 probe. (Yada et al., Nat. Astron., 2021)

Based on remote sensing and asteroid measurements, we already know that Ryugu is what we call a C-type asteroid, the most common type of asteroid in the solar system. These rocks are rich in carbon, which makes them very dark; they also have a lot of volatile elements.

In the first article, led by astronomer Toru Yada of the Japan Aerospace Exploration Agency (JAXA), an analysis of a sample from Ryugu reveals that the asteroid is extremely dark. Typically, Type C asteroids have an albedo (the measure of the amount of solar radiation reflected by a body) of 0.03 to 0.09. Asphalt has an albedo of 0.04. Ryugu’s albedo is 0.02. This means that it only reflects 2% of the solar radiation that hits it.

The asteroid is also, according to the researchers, extremely porous. According to their measurements, Ryugu has a porosity of 46%. It’s more porous than any carbonaceous meteorite we’ve ever had the chance to study, although we’ve seen more porous asteroids. This is consistent with the porosity of the asteroid as measured by remote thermal imaging and measurements made on the asteroid itself.

In the second article, a team led by astronomer Cédric Pilorget from the University of Paris-Saclay in France analyzed the composition of dust. They detected that the asteroid appears to consist of an extremely dark matrix, possibly dominated by phyllosilicates or clay minerals, although there was no clear hydration signature.

In this matrix, they identified inclusions of other minerals, such as carbonates, iron and volatile compounds.

These two papers agree that, in porosity and composition, Ryugu appears most similar to a type of meteorite classified as “CI chondrites”. This means that the meteorite is carbonaceous and similar to the Ivuna meteorite. These meteorites have, compared to other meteorites, a composition very similar to that of the solar photosphere, suggesting that they are the most primitive of all known space rocks.

Further analysis will undoubtedly be on the verge of trying to uncover more – not just on Ryugu, but what our solar system looked like as it was formed from the dust remnants of the Sun.

“Our initial laboratory observations for all returned samples demonstrate that Hayabusa2 recovered a representative, untreated (albeit slightly fragmented) sample from Ryugu,” Yada’s team wrote in their paper.

“Our data support and extend remote sensing observations which suggest that Ryugu is dominated by hydrated chondrite-like carbonaceous materials, similar to CI chondrites, but with a darker, more porous, and more brittle nature. This inference should be further corroborated by further investigation by advanced analytical methods with higher resolution and precision. “

Both articles were published in Nature astronomy. They can be found here and here.


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