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Hayabusa2 Samples Reveal Ancient Hydrothermal Activity on Asteroid Ryugu
Hayabusa2 Samples Reveal Ancient Hydrothermal Activity on Asteroid Ryugu

Hayabusa2 Samples Reveal Ancient Hydrothermal Activity on Asteroid Ryugu

September 12, 2025

In a groundbreaking discovery that reshapes our understanding of the early solar system, an international team of scientists has found clear evidence that the parent asteroid of Ryugu once hosted vast networks of flowing liquid water. The findings, published today in the journal Science Advances, are based on a detailed analysis of samples returned to Earth by the Japanese Aerospace Exploration Agency’s (JAXA) Hayabusa2 spacecraft.

The Hayabusa2 mission successfully collected 5.4 grams of material from the carbon-rich, diamond-shaped asteroid Ryugu and returned it to Earth in December 2020. Since then, scientists worldwide have been meticulously analyzing the pristine samples.

The key discovery revolves around the identification of small veins of minerals within the Ryugu samples that could only have been formed by the circulation of liquid water. These veins are composed of clay minerals and carbonates, which precipitated from water that percolated through cracks and pores in the rock on Ryugu’s much larger parent body, billions of years ago.

“This is a direct snapshot of ancient fluid activity on a large, primordial asteroid,” said Dr. Tohoku University geochemist and lead author of the study. “The composition and mineralogy of these veins tell us that the water was warm, likely between 20°C and 75°C, and that it was rich in dissolved carbon dioxide. This isn’t a catastrophic flooding event; it’s evidence of a sustained, hydrothermal system.”

The research indicates that Ryugu is a rubble-pile asteroid, a conglomerate of debris that coalesced after its massive parent body was shattered in a catastrophic impact. The new evidence suggests that this parent body was not a simple, homogenous rock but a complex, differentiated object with a distinct internal structure. The flowing water appears to have circulated through a porous core, altering minerals and redistributing organic material.

This finding has profound implications for the study of life’s origins. Carbonaceous asteroids like Ryugu are thought to have been one of the primary delivery mechanisms for water and organic compounds to the early Earth.

“We are essentially looking at the very processes that delivered the building blocks of life to our planet,” stated a co-author from the University of Tokyo. “The fact that this water was warm and interacted with rocks for millions of years creates the kind of stable, chemically rich environment that is ideal for prebiotic chemistry. It strengthens the possibility that the seeds of life were sown from space.”

The analysis also helps explain Ryugu’s surprisingly dark and porous nature. The widespread water alteration, known as aqueous alteration, transformed the asteroid’s original minerals into the clays seen today, a process that also would have created the micro-pores that give the material its low density.

In summary, the important points are:

  • Evidence of warm, flowing liquid water has been found in samples from asteroid Ryugu.

  • The water circulated through cracks on Ryugu’s ancient, larger parent body billions of years ago.

  • This process formed veins of clay and carbonate minerals now visible in the samples.

  • The discovery points to a sustained, warm hydrothermal system on the parent asteroid.

  • This finding is crucial for understanding the delivery of water and organic materials to the early Earth.

  • It provides a new window into the complex processes that occurred in the early solar system.