Reconstructing the aqueous environment of the Ryugu parent body through the speciation of multiple elements.

Ryugu's aqueous environment was highly reducing, strongly alkaline, and had lower salinity than previously estimated, with pH 10.3–11.5 and Eh -0.5 to -0.8 V.

• Why it matters: Understanding the conditions of water in asteroid parent bodies like Ryugu helps clarify the processes of aqueous alteration and the delivery of water and organics to early Earth, filling gaps in planetary evolution models.
• What they did: The study used chemical equilibrium modeling constrained by EPMA and X-ray absorption near-edge structure spectroscopy to reconstruct Ryugu’s water chemistry, focusing on element speciation and environmental parameters.
• The result: Findings suggest aqueous alteration occurred beneath a surface ice layer, with subsequent ice sublimation causing water loss, refining models of asteroid evolution and early Earth's water sources.