An analysis of the Hayabusa-2 sample of material returned to Earth from the carbon-rich, diamond-shaped, near-Earth asteroid Ryugu shows that the material is very dark, reflecting only 2% of light, porous and similar to clay, contains carbonates (a fraction of them enriched in iron) as well as compounds rich in nitrogen and hydrogen.
A carbonate-rich grain in the sample of material from the near-Earth asteroid Ryugu. Image credit: Pilorget et al., doi: 10.1038/s41550-021-01549-z.
Ryugu, also known as 1999 JU3, is a near-Earth C-type asteroid. Its name refers to Ryūgū (Dragon Palace), a magical underwater palace in a Japanese folktale.
The asteroid was discovered in May 1999 by astronomers with the Lincoln Near-Earth Asteroid Research.
It measures approximately 900 m (0.56 miles) in diameter and orbits the Sun at a distance of 0.96-1.41 astronomical units (AU) once every 474 days.
On December 6, 2020, a total of 5.4 grams of material from Ryugu was returned to Earth by JAXA’s Hayabusa-2 spacecraft in a hermetically sealed container within the re-entry capsule, and transported from South Australia to the Extraterrestrial Sample Curation Center in Sagamihara, Japan.
Ryugu is the fourth extraterrestrial body of which samples have been returned to the Earth by spacecraft, following past sample return missions by Apollo, Luna and Chang’e-5 from the Moon, stardust from comet 81 P/Wild2 and Hayabusa from near-Earth S-type asteroid Itokawa.
The Ryugu sample has sizes ranging from 8 mm, the largest average diameter, down to fine submillimeter dusts, with millimeter-scale particles being the most common.
In one study, Dr. Toru Yada from JAXA’s Institute of Space and Astronautical Science and colleagues analyzed particle size distribution, density and porosity, spectral and textural properties of the sample, and searched for inclusions and chondrules.
They found that the sample is very dark — reflecting only 2% of the light that hits it — with a high porosity of 46%, greater than any meteorite studied so far.
In a second study, Dr. Cédric Pilorget from the Institut d’Astrophysique Spatiale at the Université Paris-Saclay and colleagues determined the composition of the sample using a microscope that can acquire images at different wavelengths of light in the visible and the infrared spectrums.
They found that the sample is composed of a hydrated matrix, such as clay, with a variety of organics embedded in.
However, some individual parts are made of different substances, such as carbonates or volatile compounds.
“Our findings reveal the microscopic heterogeneous composition of Ryugu samples, while confirming in situ observations made by Hayabusa-2, suggesting that Ryugu is macroscopically uniform in structure and composition — resembling carbon-rich chondrite meteorites — but is darker, more porous and more fragile,” the authors said.
“The contents of this sample appear to be among the most primordial material available in our labs to date, forming a unique collection for studying the origin and evolution of our Solar System, whilst representing a model for the return of samples from planets in the future.”
The results were published in two papers in the journal Nature Astronomy.
_____
T. Yada et al. Preliminary analysis of the Hayabusa2 samples returned from C-type asteroid Ryugu. Nat Astron, published online December 20, 2021; doi: 10.1038/s41550-021-01550-6
C. Pilorget et al. First compositional analysis of Ryugu samples by the MicrOmega hyperspectral microscope. Nat Astron, published online December 20, 2021; doi: 10.1038/s41550-021-01549-z
