Asteroid Ryugu Formed at the Dawn of the Solar System
New research suggests Ryugu predates the formation of common solar system building blocks.
1Early Solar System Origins
Most carbon-rich meteorites contain chondrules, which are millimeter-sized molten droplets formed 4.6 billion years ago. However, samples from the asteroid Ryugu, collected by Japan's Hayabusa2 spacecraft, lack these common features. This suggests Ryugu belongs to the very first generation of planetesimals, forming before the solar system's ubiquitous chondrules even existed.
2Dating the Ancient Mineral
Researchers identified dolomite minerals within Ryugu samples to determine the asteroid's age. By measuring radioactive manganese decaying into chromium, they calculated the formation timeline. Additionally, analyzing the ratio of heavy to light oxygen atoms helped scientists estimate the temperature of water present during the crystallization process of these ancient minerals.
3Thermal History and Timing
The dolomite formed at approximately 92 degrees Celsius roughly 4.565 billion years ago. According to NASA scientist Ann Nguyen, the heat required for this process originated within the parent body and took at least one million years to accumulate. This indicates Ryugu assembled less than two million years after the first solids.
4Wave of Planet Building
The findings support theories that planetary bodies were constructed in distinct waves. Fine dust, ice, and organic matter clumped together around the newborn sun to form early precursors. Ryugu appears to be a remnant of this initial wave, preserving raw ingredients from the very beginning of our solar system's complex history.
5Scientific Community Perspective
Planetary scientist Myriam Telus, who was not involved in the study, describes the findings as high-impact for the field. She notes that while other dating methods have previously placed chondrule formation earlier, the manganese-chromium system requires further refinement. Despite these debates, experts agree that Ryugu formed during the system's earliest stages.
6Future Comparative Analysis
Ann Nguyen and her colleagues plan to apply these same dating methods to samples from the asteroid Bennu, collected by NASA's OSIRIS-REx mission. Comparing Bennu and Ryugu will help researchers determine if these two bodies share a common parent asteroid or if they are simply siblings from the same early solar epoch.
7Context of Solar Evolution
The formation of planetesimals is a critical phase in solar system development, marking the transition from simple dust to larger, complex bodies. By studying these ancient asteroids, scientists gain insight into the chemical and thermal conditions present 4.5 billion years ago, long before the major planets reached their current stable configurations.
8Significance of Sample Return
Missions like Hayabusa2 and OSIRIS-REx provide direct physical evidence that remote sensing cannot match. By bringing pristine material back to Earth, researchers can perform high-precision laboratory analyses. These samples act as time capsules, allowing scientists to reconstruct the chaotic environment that existed during the birth of our planetary neighborhood.