Media release

From: Springer Nature

Planetary science: A long fluid history for near-Earth asteroid Ryugu’s parent

Fluids may have flowed within the parent body of the near-Earth asteroid Ryugu more than one billion years after it formed, according to research published in Nature. The findings indicate that such bodies, known as carbonaceous asteroids, may have retained two to three times more water than previously thought. Understanding the history of fluids on carbonaceous asteroids is important as it can have implications for the origin of water on terrestrial planets.

Carbonaceous asteroids, rich in carbon and water, are the most common objects in the outer regions of the asteroid belt of the Solar System. They are thought to have formed from dust and ice in the outer Solar System and may have delivered water and other substances to the terrestrial planets. Understanding the aqueous activity in such asteroids can provide insights into their evolution. Although some analyses of carbonaceous asteroids, including Ryugu, have identified fluid–rock interactions within a few million years after parent body formation, longer-term aqueous histories have been poorly understood.

The Hayabusa2 spacecraft, from the Japan Aerospace Exploration Agency, retrieved samples from the near-Earth, carbonaceous asteroid Ryugu in 2019. An analysis of these samples provides evidence for a late fluid flow, Tsuyoshi Iizuka and colleagues report. They present isotopic data documenting the decay of lutetium-176 to hafnium-176 (¹⁷⁶Lu–¹⁷⁶Hf), a system used for dating rocks but adapted to constrain the timing of aqueous fluid flow in Ryugu’s parent body. An apparent excess of hafnium-176 is detected, which indicates that lutetium was transported by fluids more than one billion years after the formation of the parent body. Such a late fluid flow may have been triggered by an impact that generated heat, melting ice and opening fractures in the rock that allowed fluid to flow, the authors propose. These findings suggest that carbonaceous asteroids may have had the potential to deliver two to three times more water to terrestrial planets than previously thought, the authors conclude.