Asteroid Ryugu. Credit: ©2025 Jaxa, UTokyo & collaborators (CC-BY-ND)Scientists have uncovered evidence that liquid water flowed on the asteroid Ryugu more than a billion years after it formed. “We found that Ryugu preserved a pristine record of water activity, evidence that fluids moved through its rocks far later than we expected,” says Associate Professor Tsuyoshi Iizuka from the University of Tokyo, Japan. When the researchers examined the asteroid samples, they discovered the ratio of hafnium-176 to lutetium-176 was higher than expected. Diagram showing how the researchers think the evolution of Ryugu played out over at least a billion years.