It has been over a year since the Hayabusa2 probe delivered its precious cargo of dust from an alien space rock, and we are finally getting a more detailed glimpse of what makes up asteroid Ryugu.
In two papers published today, international teams of scientists have revealed that, in accordance with analyses conducted by the probe while at the asteroid, Ryugu is very dark, very porous, and some of the most primitive Solar System material we've ever had access to here on Earth.
The results are very cool. The sample is one of the best tools for understanding the composition of the dust from which the inner Solar System objects coalesced since the asteroid has remained more or less unchanged since the formation of the Solar System 4.5 billion years ago.
The Hayabusa2 returned samples seem to be among the most primordial materials available in our laboratories, according to one of the teams in their paper. The samples are a unique collection, which may contribute to revisiting the paradigms of Solar System origin and evolution.
A sample return mission has been conducted on the asteroid known as 1999 JU3. Itokawa's sample return mechanism failed and only a small amount of dust reached Earth in 2010.
It is about a kilometer across, with a ridge around its equator, and travels an elliptical path around the Sun, then out to Mars. It took a lot of skill and planning to get to the asteroid and return the dust.
After it worked, 5.4 grams of precious asteroid dust were returned and analyzed, and Hayabusa2 sailed off for a series of rendezvous with other asteroids.
The Hayabusa2 probe returned samples of ryugu. Yada et al. Astron., 2021.
The most common type of asteroid in the Solar System is called a C-type asteroid, and we already know that it is called Ryugu. The rocks are rich in carbon and have a lot of volatile elements.
An analysis of a sample from the asteroid shows that it is extremely dark. The albedo is the measure of how much solar radiation a body reflects. The albedo is 0.04. The albedo is 0.02. It reflects less than 2% of the solar radiation that hits it.
The researchers determined that the asteroid is porous. According to their measurement, it has a porosity of 46 percent. We have seen more porous asteroids, but that is more porous than any carbonaceous meteorite. This is consistent with the asteroid's porosity as measured by remote thermal images and by the measurement of the asteroid itself.
In the second paper, a team led by astronomer Cédric Pilorget of the Université Paris-Saclay in France analyzed the composition of the dust. The asteroid seems to be made of a dark matrix with a lack of a hydration signature.
They identified carbonates, iron, and volatile compounds in the matrix.
Both papers agree that, in terms of composition and porosity, it seems like a type of meteorite called "CI chondrites". The Ivuna meteorite is carbonaceous. The composition of these meteorites is similar to that of the solar photosphere, suggesting they are the most primitive of all known space rocks.
More in-depth analyses will be on the way to discover more about the Solar System as it was forming from the Sun's leftover dust.
Yada's team wrote in their paper that Hayabusa2 retrieved a representative sample from the sample they returned.
Our data supports the idea that the hydrous carbonaceous chondrite-like materials are dominated by a darker, more porous and more fragile nature. State-of-the-art analytical methods with higher resolution and precision should be used to corroborate the inference.
Nature Astronomy has published two papers. They can be found here.
