Scientists have uncovered surprising evidence that the asteroid Ryugu contained liquid water much more recently than previously thought. Using an 80-milligram sample from this near-Earth asteroid, researchers determined that water existed within Ryugu’s structure for a significantly longer period, indicating its parent asteroid hosted liquid water without evaporating or chemically reacting with surrounding minerals.
Geochemist Tsuyoshi Iizuka from the University of Tokyo expressed his astonishment at the findings: “It was a genuine surprise! We found that Ryugu preserved a pristine record of water activity, evidence that fluids moved through its rocks far later than we expected.”
New Insights into Asteroid Formation
Ryugu originated as part of a “planetesimal,” the building block of planets, which formed in the outer regions of our Solar System approximately 4.565 billion years ago. This protoplanet, made from accumulated ice and dust, likely thawed about a billion years after its formation. Researchers speculate that a collision may have fractured and heated the planetesimal, melting its buried ice and allowing liquid water to flow.
The implications of this discovery extend beyond Ryugu itself. If collisions resulted in water-laden asteroids being propelled into the inner Solar System, they might have delivered two to three times more water to early Earth than current models suggest. The longstanding question of how water first arrived on our planet could see new answers, as Ryugu may provide vital clues.
Challenging Existing Theories
The traditional understanding of water distribution in the early Solar System has faced challenges, particularly regarding the apparent scarcity of moisture. The findings from Ryugu indicate that some asteroids, previously thought to be too dry, may have held onto ice for extended periods. Iizuka noted, “The idea that Ryugu-like objects held on to ice for so long is remarkable. This suggests that the building blocks of Earth were far wetter than we imagined.”
Chemical analysis of Ryugu’s samples was conducted through the radioactive decay of lutetium-176 (176 Lu) to hafnium-176 (176 Hf). The presence of liquid water disrupted the decay process, resulting in a different ratio of these elements compared to terrestrial meteorites. As Iizuka explained, “This meant we had to carefully rule out other possible explanations and eventually concluded that the Lu-Hf system was disturbed by late fluid flow.”
Although Ryugu is currently dry, its chemical composition provides insights into the conditions that prevailed in the early Solar System. The study, published in the journal Nature, reinforces the asteroid hypothesis for Earth’s water sources.
As research continues, the implications of Ryugu’s findings may reshape our understanding of how water arrived on Earth and the role of asteroids in our planet’s history.
