Ancient Grains of Dust Reveal Life Story of Solar System Asteroid
Scientists have analyzed grains collected from asteroid Ryugu and discovered that this carbon-rich rock has a complex history involving multiple migrations through the Solar System. These findings indicate that asteroids contain valuable records of different periods throughout the history of the Solar System.
Asteroid Ryugu, classified as a C-type asteroid, is rich in carbon and water and is typically found in the Main Belt of asteroids between Mars and Jupiter. However, its orbit is very close to Earth’s, suggesting that it was disrupted and sent out of the asteroid belt long ago.
The Japan Aerospace Exploration Agency’s Hayabusa2 probe, launched in 2014 as a sample return mission, surveyed Ryugu from 2018 to 2019 before returning home in 2020. In addition to collecting samples, the probe also discovered that Ryugu is not a single large chunk of rock but rather a “rubble pile” consisting of smaller rocks bound together by gravity.
While Ryugu shares similarities with asteroids in the Main Belt, studies on the samples brought back to Earth reveal that some of the minerals in the rubble pile are more consistent with material from the outer Solar System. For instance, Ryugu has a significant amount of organic matter similar to comets, which predominantly originate from the outer Solar System.
Dr. Rosario Brunetto from the University of Paris-Saclay and her international team further examined grains rich in olivine, pyroxene, and amorphous silicates, which have been least altered by the asteroid’s water content. Using infrared spectrometry, they found that these grains reflect infrared light profiles similar to objects from the outer Solar System, suggesting a more distant origin than the Main Belt.
The researchers propose that Ryugu’s primary parent body was initially formed in the outer Solar System as a planetesimal, the building blocks of planets. However, something disrupted its growth, potentially breaking it apart and subsequently sending it to the Main Belt, where it underwent transformation due to water alteration.
According to the researchers, asteroid Ryugu serves as an essential record of the Solar System’s evolution. The pristine lithologies of the Ryugu samples contain anhydrous grains that are spectrally similar to some outer Solar System primitive bodies, providing valuable information about the formation and evolution of planetesimals.
The study, published in The Astrophysical Journal Letters, highlights the importance of analyzing ancient grains of dust to unlock the life stories of Solar System asteroids and gain insights into the history of our celestial neighborhood.