Asteroid Ryugu and some carbonaceous meteorites are considered chemically primitive because they preserve much of the early solar system’s original composition. At the same time, these materials underwent extensive reactions with water after forming, altering many of their initial minerals. This apparent contradiction has remained a longstanding problem in cosmochemistry.
A research team led by Kanazawa University and The University of Tokyo used synchrotron X-rays at the KEK-PF and SPring-8 facilities to examine Ryugu samples and carbonaceous meteorites. Their findings, published in Communications Earth & Environment, point to a previously underrecognized material as a possible explanation.
The researchers found that, alongside the better-known minerals serpentine and saponite, the samples commonly contain a poorly crystalline magnesium silicate hydrate known as M-S-H. Using soft X-ray absorption spectroscopy, they identified this component in Ryugu and carbonaceous meteorites.
M-S-H can accommodate a broad range of magnesium-to-silicon ratios. According to Keisuke Fukushi of Kanazawa University, that flexibility may have allowed water-rock reactions to occur without eliminating chemical differences that already existed within the asteroids from which the materials came.
Laboratory experiments and previously published solubility data showed that M-S-H with different magnesium-to-silicon ratios can remain stable under similar aqueous conditions. The team also suggests that some serpentine and saponite in the samples may have formed when precursor M-S-H transformed into more crystalline minerals.
The results indicate that different alteration minerals could develop while preserving compositional variations from one location to another. M-S-H may therefore help explain how Ryugu and related meteorites were extensively altered by water yet retained chemical characteristics inherited from the early solar system.
The study, by Reon Okumura and colleagues, is titled “Pervasive poorly crystalline Mg-rich hydrous silicate material in C-type asteroid matrices.” It was published in 2026 in Communications Earth & Environment and has the DOI 10.1038/s43247-026-03958-2.
Sources: Phys.org.