This water flow took place on ancient asteroids over a billion years after their formation, likely due to the heat generated by melting ice, which caused rock fractures that facilitated water movement. JAXA’s Hayabusa-2 Spacecraft.
This image of the asteroid was taken on June 26, 2018, by JAXA’s Hayabusa-2 Spacecraft optical navigation camera – telescopic (ONC-T). Image credits: JAXA / University of Tokyo / Kochi University / Ricchiho University / Nagoya University / Chiba University of Technology / Nishimura University / Aizu University / AIST.
Ryugu is a CG-type asteroid close to Earth and part of the Polana family of impact asteroids.
The diamond-shaped body, also known as 1999 JU3, was identified by astronomers in May 1999 during asteroid studies near Lincoln.
Its diameter measures about 900 m (0.56 miles), and it orbits the Sun at a distance of 0.96-1.41 Astronomical Units (AU) every 474 days.
“We have a relatively good understanding of how the solar system was formed, though many gaps remain,” said Shiyoshijima, a researcher at the University of Tokyo.
“One gap in our knowledge is how Earth acquired its water.”
“It has long been known that carbonaceous asteroids, originating from ice and dust in the outer solar system, have contributed water to Earth.”
“We discovered that Ryugu preserves an unaltered record of water activity, indicating that liquid water moved through the rock much later than previously anticipated,” added Dr. Ikemoto.
“This shifts our understanding of the long-term fate of water on asteroids. The water has remained for an extended period and hasn’t been depleted as quickly as we thought.”
In this study, the authors examined the isotopes of lutetium (Lu) and hafnium (HF), with the radioactive decay from lutetium-176 to hafnium-176 serving as a sort of clock to gauge geological processes.
The expected presence of these isotopes in the studied sample was hypothesized to correlate with the asteroid’s age in a predictable manner.
However, the ratio of Hafnium-176 to Lutetium-176 was significantly unexpected.
This strongly suggests to researchers that the liquid effectively washed away lutetium from the rocks containing it.
“We anticipated that Ryugu’s chemical signatures would align with certain meteorites currently under examination on Earth,” Dr. Iizuka stated.
“However, the results were strikingly different, necessitating the careful elimination of other possible explanations, ultimately concluding that the Lu-HF system was hindered by a delayed liquid flow.”
“The most probable triggers involved the parent body of Ryugu’s larger asteroid, which disrupted the rocks, melting the embedded ice and allowing liquid water to permeate the body.”
“It was truly surprising! This impact event could be the catalyst for the parent body disruption.”
One of the crucial implications is that carbon-rich asteroids may be a significant source of water for Earth, supplying far more than previously estimated.
Ryugu’s parent body seems to have retained ice for over a billion years. This suggests that similar bodies impacting the young Earth could have delivered 2-3 times more water than standard models predict, significantly influencing the planet’s early oceans and atmosphere.
“The notion that a Ryugu-like object has preserved ice for such an extended time is remarkable,” Dr. Ikemoto remarked.
“It implies that Earth’s components were far wetter than we had imagined.”
“This prompts a reevaluation of the initial conditions for the planetary water system.”
“It’s still early to draw definitive conclusions, but my team and others may build on this research to clarify various aspects, including how our planet became habitable.”
The findings will be published in the journal Nature.
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T. Iizuka et al. Late fluid flow of primitive asteroids revealed by Lu-HF isotopes of Lu. Nature. Published online on September 10th, 2025. doi:10.1038/s41586-025-09483-0
Source: www.sci.news
