Scientists have found that liquid water flowed on the surface of the asteroid that birthed the near-Earth object (NEO) Ryugu much later than it was expected, indicating impacts might've melted ice, allowing liquid water to flow through rocks.
Ryugu, a spinning-top-shaped near-Earth object, is a carbonaceous asteroid formed from ice and dust in the outer solar system. Scientists study it to get insights into planet formation and the potential delivery of water to Earth via asteroids.
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The surprising discovery was made possible by studying rock samples collected by Japan's Hayabusa2 probe between 2018 and 2019. It had returned to Earth on December 5, 2020.
According to the research published on Wednesday (September 10) in the journal Nature, these samples revealed that water existed in liquid form a billion years after Ryugu's parent body formed.
The latest findings have challenged previous assumptions about asteroid water activity. The scientists previously thought that the asteroid water activity only lasted for the earliest moments of solar system history.
"We found that Ryugu preserved a pristine record of water activity, evidence that fluids moved through its rocks far later than we expected," research team member Tsuyoshi Iizuka, a scientist at the University of Tokyo, said as quoted by Space.com.
"This changes how we think about the long-term fate of water in asteroids. The water hung around for a long time and was not exhausted so quickly as thought."
The researchers have studied lutetium and hafnium isotopes in Ryugu samples, finding evidence of fluid washing out lutetium, pointing to late fluid flow. This suggests carbon-rich asteroids like Ryugu might've delivered more water to primordial Earth than estimated, impacting early oceans and atmosphere.
"We thought that Ryugu's chemical record would resemble certain meteorites already studied on Earth," Iizuka said. "But the results were completely different. This meant we had to carefully rule out other possible explanations and eventually concluded that the lutetium-hafnium system was disturbed by late fluid flow."
"The most likely trigger was an impact on a larger asteroid parent of Ryugu, which fractured the rock and melted buried ice, allowing liquid water to percolate through the body. It was a genuine surprise! This impact event may also be responsible for the disruption of the parent body to form Ryugu."
The discovery underscores how asteroids like Ryugu hold "fossil records" of early solar system materials. The findings reshape understanding of planetary building blocks and Earth's water origins.
