A study published in Science confirms that the parent body of asteroid Ryugu formed within 2 million years of the solar system’s birth, based on analysis of Hayabusa2 samples. Researchers from Hokkaido University and collaborators used radioisotope dating of dolomite to trace its early history, while another team identified an unexpected mineral that challenges assumptions about Ryugu’s origins.
Scientists have pinpointed the formation of Ryugu’s parent body to within 2 million years of the solar system’s birth, a discovery that reshapes understanding of early planetary processes. The findings, published in the journal Science, rely on mineral analysis of samples collected by Japan’s Hayabusa2 mission, which returned material from the asteroid in 2020. Researchers from Hokkaido University and other institutions used radioisotope dating of dolomite—a carbonate mineral found in the samples—to determine that the parent body formed 4.56 billion years ago, just 2 million years after the solar system began.
Formation Timeline Confirmed
The research team, led by Hokkaido University Associate Professor Noriyuki Kawasaki, analyzed temperature changes in Ryugu’s parent body by modeling the conditions under which dolomite formed. The mineral, which crystallized at around 90°C, provided a key timestamp. By accounting for the time required to reach that temperature through radioactive heating, the scientists concluded the parent body formed less than 2 million years after the solar system’s inception, roughly 4.6 billion years ago.
Earlier theories suggested Ryugu was a fragment of a larger body that broke apart, but the exact timing of its parent body’s formation remained unclear. This study fills a critical gap, according to Hokkaido University Associate Professor Noriyuki Kawasaki, who emphasized the importance of refining models of early solar system dynamics. The results align with findings from another group of researchers, who independently dated the parent body to less than 2 million years after the solar system’s formation, as reported by NHK World and The Japan Times.
The samples, collected from Ryugu’s surface, contain hydrated minerals formed when ice melted and reacted with rock inside the parent body. This process, driven by heat from radioactive decay, created conditions for the formation of minerals like dolomite. The team’s use of a new error-correction method for radioisotope dating improved the accuracy of their timeline, as noted in UA.NEWS and adnkronos.com.
Unexpected Mineral Challenges Assumptions
A separate study, published in Meteoritics & Planetary Science in May 2025, uncovered an anomaly in Ryugu’s composition: the presence of djerfisherite, a potassium-rich iron-nickel sulfide typically found in enstatite chondrites. This mineral, which forms in highly reduced environments, was never before detected in CI chondrites or other Ryugu grains, according to Masaaki Miyahara, an associate professor at the Graduate School of Advanced Science and Engineering, Hiroshima University.
Its occurrence is like finding a tropical seed in Arctic ice—indicating either an unexpected local environment or long-distance transport in the early solar system,
Miyahara said. The discovery suggests that Ryugu’s parent body may have incorporated materials from diverse regions of the solar system, challenging the notion of its uniform composition. The team proposed two hypotheses: either djerfisherite was transported from another region during the parent body’s formation, or it formed locally under previously unrecognized conditions.
While the mineral’s origin remains uncertain, its presence adds complexity to models of early solar system mixing. The parent body of Ryugu is believed to have formed in the outer solar system, where water and carbon dioxide existed as ice. Heat from radioactive decay eventually melted this ice, creating the hydrous minerals observed in the samples. However, the djerfisherite’s formation conditions—requiring temperatures above 350°C—suggest localized heating events or external influences, as outlined in Sciencedaily.com.
Implications for Planetary Formation
The findings from both studies contribute to broader efforts to reconstruct the early solar system’s evolution. By understanding how small bodies like Ryugu formed and evolved, scientists can better model planetary accretion and material transport. Ultimately, our goal is to reconstruct the early mixing processes and thermal histories that shaped small bodies like Ryugu,
said Miyahara, highlighting the significance of these insights for planetary science.
Previous research, including analyses by researchers including those from the Museum, has shown that Ryugu’s parent body likely formed in the outer solar system and was later shattered by a collision. The fragments coalesced to form Ryugu, which now offers a window into the conditions of the early solar system. The new data refine these models, providing a more precise timeline for the formation of primitive asteroids.
The Hayabusa2 mission’s return of pristine samples has been pivotal in these discoveries. Unlike meteorites, which undergo changes during their journey to Earth, Ryugu’s samples remained largely unaltered, preserving their original composition.
As researchers continue to analyze the samples, they aim to uncover more about the solar system’s earliest days. The presence of djerfisherite and the precise dating of Ryugu’s parent body underscore the complexity of planetary formation, offering new questions about the processes that shaped our cosmic neighborhood.
