By BlueShift and AFP | 2025-12-02

New analysis of samples retrieved from the distant asteroid 162173 Ryugu by Japan's Hayabusa-2 probe suggests that Earth's building blocks were "far wetter" than previously imagined.

Research on a tiny portion of the 5.4 grams of rock and dust collected from the Ryugu ("Dragon Palace") asteroid offers new insights into the early life of our planet.

Scientists believe Earth has oceans, lakes and rivers because it was hit with water-carrying asteroids up to 4.5 billion years ago.

Previous research has shown that water existed on asteroids in the solar system's early years. But scientists used to believe that this water would have dissipated relatively quickly amid the heat of the solar system's formation.

"Here we learned for the first time that water existed (in the form of ice) for one billion years," associate professor of the University of Tokyo's Department of Earth and Planetary Science Tsuyoshi Iizuka told AFP.

The finding "forces us to rethink the starting conditions for our planet's water system," said Iizuka, who is an author of the study published September 10 in the Nature journal.

The findings are the latest in a trove of research done on the sample retrieved from Ryugu by Japan's Hayabusa-2 probe and returned to Earth in 2020.

The Ryugu asteroid, around 185 million miles from Earth, is estimated to be between 100 million and one billion years old. It is thought to be formed from fragments scattered after the destruction of its parent body.

Surprising findings

The new study suggests asteroids may have retained water in the form of ice and hydrated minerals.

This means asteroids striking a young Earth could have carried water in quantities two to three times larger than previously thought, significantly affecting the planet's early oceans and atmosphere, the study said.

Using a radioactive decay system, researchers found evidence that water flowed on Ryugu more than one billion years after the formation of its parent.

That flow may have been triggered by an impact that generated heat, melted ice and opened rock fractures, they said.

"I was surprised by the findings," Iizuka said, adding that he plans to investigate whether similar water activity happened on other asteroids.

His team also hopes to trace how water was stored, mobilized and finally delivered to Earth.

NASA and other institutes are also studying samples brought back from the 4.5-billion-year-old asteroid Bennu in 2023.

A better understanding of asteroid history "will help us to unravel the evolution of the solar system," Iizuka said.

JAXA's Hayabusa-2 probe

In October 2019, the Japan Aerospace Exploration Agency (JAXA) Hayabusa-2 probe landed on Ryugu for the last time, hoping to collect samples that could shed light on the evolution of the solar system.

It was the second time the probe had landed on the desolate asteroid, as part of a complex mission that also has involved sending European and Japanese rovers and robots to Ryugu's surface.

The mission hoped to collect pristine materials from beneath its surface that could provide insights into what the solar system was like at its birth.

To get at those materials, an "impactor" had been fired from Hayabusa-2 towards Ryugu in April 2019, creating a crater on the asteroid's surface and stirring up material that had not been previously exposed to the atmosphere.

It was the first-ever artificially created crater on an asteroid, JAXA said.

In 2005, NASA's Deep Impact project succeeded in creating an artificial crater on a comet, but only for observation purposes.

In February 2019, Hayabusa-2 landed briefly on Ryugu and fired a bullet into the surface to puff up dust for collection.

Hayabusa-2, which launched in December 2014, is about the size of a large refrigerator and is equipped with solar panels to keep it powered. It is the successor to JAXA's first asteroid explorer, Hayabusa ("Falcon").

That probe returned with dust samples from a smaller asteroid in 2010.