New analysis of samples collected by Japan's Hayabusa2 spacecraft from asteroid Ryugu has provided strong evidence of water flow occurring on the asteroid's parent body over a billion years after its formation. This significant finding, detailed in the journal Nature, challenges the long-held scientific belief that substantial water activity on asteroids was primarily limited to the solar system's earliest stages. The research, spearheaded by Tsuyoshi Iizuka of the University of Tokyo, employed lutetium-hafnium (Lu-Hf) isotopic analysis to precisely date this fluid flow event.
The study suggests that an impact on Ryugu's original parent body created fractures. These fractures subsequently allowed buried ice to melt, enabling liquid water to infiltrate the asteroid's internal structure. This extended presence of water on Ryugu's parent body indicates that similar asteroids could have served as a more consistent source of water for Earth over prolonged periods. Such an extended delivery mechanism might have played a more crucial role in shaping Earth's early oceans and atmosphere than previously understood.
The Hayabusa2 mission, a major endeavor by the Japan Aerospace Exploration Agency (JAXA), successfully retrieved approximately 5.4 grams of material from Ryugu in 2020. These samples have yielded unprecedented insights into the composition and history of primitive asteroids, significantly enhancing our understanding of the early solar system. Ryugu is identified as a carbonaceous asteroid, a type known for its high content of carbon and water. The returned samples exhibit characteristics comparable to CI chondrites, which are considered highly representative of the solar system's primordial materials due to their chemical composition closely mirroring that of the Sun.
The discovery of late-stage fluid flow on Ryugu, confirmed by the Lu-Hf isotopic data, implies that asteroids may have retained ice for considerably longer durations than previously assumed. This recalibrates the potential for these celestial bodies to have delivered substantial quantities of water to early Earth, possibly two to three times more than current models estimate. This groundbreaking research not only deepens our knowledge of asteroid evolution but also necessitates a re-evaluation of the processes by which Earth and other terrestrial planets acquired their essential water resources.