Liquid Water Persistedโฃ on โคasteroid โคRyugu’s Parent Bodyโค forโข Billions โof years, โNew Analysis Reveals
TOKYO – An international team led โby University of Tokyo researcher โTsuyoshi Iizuka hasโข discovered evidence that โคliquid water โflowed through the parent asteroid of Ryugu for a surprisingly long โperiod – over a billion years – challengingโ previous assumptions about โthe delivery of water to Earth. Theโข findings,โฃ published September 10, 2025, in the journal Nature, suggest carbon-rich asteroids may have contributed substantially more water toโค ourโ planet than previously estimated.
Researchers analyzed isotopes of lutetium (Lu) and hafnium (Hf) in samples returned from the asteroid Ryugu by the โHayabusa2 mission. โขThe ratio โคof hafnium-176 to lutetium-176 was unexpectedly high,โข indicating thatโข lutetium hadโฃ been washed out of theโค rocks by a fluid. โ
“We found that Ryugu preserved a pristineโฃ record ofโ water activity, evidence that fluids moved through its rocks far later than we expected,” Dr.Iizuka said. “This changes how we think about the long-term fate of water in asteroids.โ The water โฃhung around for a long time and was not โคexhausted โso quickly as thought.”
The team believes a large impact on Ryugu’s parent body fracturedโข the rock โฃand melted buried ice, โคallowing liquid water โto percolate through the asteroid’s interior.This impact event may haveโข also been โฃresponsible for the breakup of the parent body, ultimately forming Ryugu.
The prolonged presence โขof โwater on โฃRyugu’s parent body has significant โimplications for understanding Earth’s early oceans and atmosphere. โScientists โestimate that similar bodiesโฃ impacting a young Earth couldโฃ have โdelivered two to three timesโข more water than current modelsโ predict.
“It seems Ryugu’s parent โคbody retained ice forโฃ overโ a billion years, meaning similarโ bodiesโ striking a young Earth could โhave carried anโค estimated two to three times more water โขthanโ standard โฃmodels account for,” Dr. Iizuka explained. “The idea that Ryugu-like objects held on to iceโ for so long is remarkable. โคIt suggests that the building blocks of Earth were far wetter than we imagined.”
The researchโฃ prompts a reevaluation ofโ the conditions necessary โfor โEarth to become habitable. “This forcesโ us toโ rethink the โstarting conditions for our planet’s water system,”โ Dr.โ iizuka stated. “Thoโ it’s too early to say โขfor โคsure, my teamโฃ and others might build onโ this research to clarifyโฃ things, including how and whenโข our Earth became โฃhabitable.”
It’s long been understood that carbonaceous asteroids like Ryugu formed in the outer Solar System and supplied water to Earth. This new study provides โคcrucial insight into the longevity of that water source.