Recent isotopic analysis of samples from asteroid Ryugu has provided compelling evidence that liquid water persisted within its parent body for over a billion years after formation. This discovery challenges the long-held scientific assumption that significant water activity on asteroids was primarily limited to the solar system's early stages. The findings suggest a more substantial and prolonged role for asteroids in delivering water to early Earth, potentially reshaping our understanding of how our planet's oceans formed.
Scientists examining the lutetium-176 to hafnium-176 isotope ratio in the Ryugu samples detected an unexpectedly high ratio. This anomaly indicates that a fluid had permeated the asteroid's parent body, altering its isotopic composition. The most plausible explanation for this alteration is an impact event that melted buried ice, facilitating the percolation of liquid water through the asteroid's rocky interior. This late-stage fluid activity on Ryugu's parent body occurred over a billion years after its initial formation, a timescale far exceeding previous estimations.
This revelation has significant implications for our understanding of planetary formation and the origins of Earth's water. Carbon-rich asteroids like Ryugu, which formed in the outer solar system approximately 4.56 billion years ago, are considered pristine remnants of the early solar system. The extended presence of liquid water within these bodies suggests they may have been far wetter than previously imagined, potentially delivering two to three times more water to early Earth than current models account for. This could equate to 60 to 90 times the mass of Earth's current oceans.
The research, published in Nature, indicates that asteroids may have delivered water not only as hydrated minerals but also as ice, contributing significantly to Earth's early oceans and atmosphere. The analysis of Ryugu samples, collected by Japan's Hayabusa2 mission and returned to Earth in December 2020, has provided a unique window into the solar system's early history. The pristine nature of these samples, untouched by Earth's atmospheric entry or surface processes, offers a direct glimpse into the materials that coalesced to form our solar system. Further studies on these samples are expected to continue for years, with ongoing comparisons being made to samples from NASA's OSIRIS-REx mission to asteroid Bennu. The detailed isotopic analysis, particularly of the lutetium-hafnium system, is crucial for dating these ancient materials and understanding the timeline of water activity. This extended period of water presence on Ryugu's parent body forces a re-evaluation of the initial conditions for Earth's water system and the processes that shaped our planet's habitability.