The Asteroid Ryugu Once Harbored Liquid Water

A significant amount of water once cascaded along the surface of an asteroid, indicating that asteroids may have delivered more water to Earth than previously believed.

The source of Earth’s water remains somewhat enigmatic. Although incoming asteroids are considered potential contributors, skepticism exists regarding their ability to supply the vast quantities of water present on Earth today.

Carbonate asteroids develop from dust and ice in the outer solar system. In 2019, Japan’s Hayabusa 2 spacecraft landed on Ryugu and collected 5.4 grams of material, returning it to Earth in 2020.

Initial images of Ryugu suggested it was drier than anticipated, but further studies revealed the presence of cracks once filled with vital elements, including water.

Early dating of the samples indicated that the asteroid was among the oldest celestial objects, originating around 460 million years ago.

However, when Tsuyoshi Itsuka from the University of Tokyo and his team assessed its age using the radioactive decay of lutetium-176 in tiny asteroid samples, they found something intriguing.

“Our analysis estimates the age of the Ryugu sample at about 4.8 billion years, significantly predating the solar system,” notes Ikemoto. “This indicates the timing of Ryugu’s sample collection is critical.”

Instead, the researchers believe that roughly a billion years after its parent body was formed, Ryugu was warmed enough to convert ice into water, which in turn removed some lutetium-176, complicating dating techniques.

Solar radiation warms only the surface ice to about 40 centimeters, while the Ryugu samples were extracted from much deeper layers. Researchers suggest that collisions with other celestial objects may explain how the interior of the parent body was heated.

By estimating the volume of water required to alter the lutetium-176 levels in the Ryugu samples, the team concluded that the asteroid consists of roughly 20-30% water.

Ikemoto asserts that asteroids are believed to have delivered water to Earth in mineral form. “Our findings imply that they can actually provide water as both minerals and ice,” he adds.

The research highlights the value of sample-return missions, according to Jonti Horner from the University of South Queensland, who was not involved in this study. “By retrieving samples directly, we eliminate Earth’s interference, enhancing the validity of our findings,” Horner explains.

“This suggests that these bodies were wetter than previously thought, allowing us to better understand the origins of Earth’s oceans as we analyze early planetary formation,” he concludes.

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