Ancient grains of dust have become the unexpected storytellers of an asteroid’s life, providing valuable insights into the history of our Solar System. Recent analysis of grains collected from asteroid Ryugu has revealed that the carbon-rich rock had a much more complex journey than previously thought. It originated far from the Sun, migrated through the asteroid belt, and eventually settled at a distance from the Sun similar to Earth’s orbit. This discovery suggests that asteroids like Ryugu can carry records of different periods in the Solar System’s history, making them invaluable sources of information.
Ryugu, a C-type asteroid, belongs to the most common type of asteroids found in the Main Belt between Mars and Jupiter. However, what sets Ryugu apart is its orbit, which closely resembles that of Earth. This peculiar characteristic indicates that Ryugu went through a disruptive event that expelled it from the asteroid belt. To unravel the mysteries of this unconventional space rock, the Japan Aerospace Exploration Agency’s (JAXA) Hayabusa2 probe embarked on a sample return mission, sending back grains of Ryugu for analysis.
The samples collected from Ryugu have sparked a growing number of studies, shedding light on its complex origins. Researchers, led by astrophysicist Rosario Brunetto of the University of Paris-Saclay, closely examined grains rich in olivine, pyroxene, and amorphous silicates. These specific grains experienced minimal alteration from the water present on the asteroid. Using infrared spectrometry, the team discovered that the reflected profile of infrared light from these grains resembles objects originating from the outer Solar System. The similarity is strikingly apparent when compared to asteroid Hektor, a Trojan sharing Jupiter’s orbit, Comet Hale-Bopp, and interplanetary dust likely of cometary origin.
The findings from the analysis of Ryugu’s grains indicate that its primary parent body was a planetesimal, a building block for planets, that initially formed in the outer Solar System. This suggests that the asteroid incorporated ingredients from the outer regions during its formation. However, something disrupted its growth, potentially fragmenting it and causing it to migrate to the Main Belt. Once there, Ryugu underwent transformation through exposure to water.
The unique characteristics of Ryugu make it an essential record of the Solar System’s evolution. The researchers emphasize that the returned samples from Ryugu offer a significant opportunity to gain insights into the source of asteroid spectral diversity. These samples contain pristine lithologies with anhydrous grains, similar in spectral composition to primitive bodies from the outer Solar System. Ryugu, therefore, holds the potential to reveal several reservoirs of anhydrous primitive dust that carry valuable information about the formation and evolution of planetesimals in the protoplanetary disk.
The analysis of ancient grains of dust from asteroid Ryugu has given us a glimpse into the asteroid’s complex journey through the Solar System. From its distant origins in the outer Solar System to its migration to the Main Belt, Ryugu’s story is one of disruption and transformation. By studying the grains that have remained largely unchanged by water, researchers have unlocked clues to the asteroid’s origins and the evolution of the Solar System. Ryugu’s unique composition and history make it a treasure trove of information, shining a light on the mysteries of our celestial neighborhood.
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