This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Asteroid Ryugu and some carbonaceous meteorites, which are thought to have similar origins in the early solar system, are known as chemically "primitive" materials because they preserve the chemical composition of the early solar system remarkably well. Yet these rocks also reacted extensively with water after they formed, transforming many of their original minerals into new ones.
When rocks react with water, elements can dissolve into the fluid or move from one place to another, potentially altering the original chemical composition. This seemingly contradictory combination—extensive reaction with water while preserving the chemical composition of the early solar system—has long been one of the puzzles of cosmochemistry. A research team led by Kanazawa University and The University of Tokyo used powerful X-rays at the large-scale synchrotron facilities KEK-PF and SPring-8 to examine these extraterrestrial materials in detail.
They identified a previously overlooked material that may provide an important clue to this longstanding puzzle. The paper is published in the journal Communications Earth & Environment. In the conventional mineralogical picture, aqueous alteration of primitive carbonaceous meteorites has been interpreted mainly in terms of the formation of serpentine and saponite.
Using synchrotron-based soft X-ray absorption spectroscopy, however, the researchers found that, in addition to the well-recognized serpentine and saponite, a previously underrecognized component resembling poorly crystalline magnesium silicate hydrate (M-S-H) is widespread in Ryugu and carbonaceous meteorites. "What makes M-S-H particularly interesting is that it can accommodate a wide range of magnesium-to-silicon ratios," says Keisuke Fukushi of Kanazawa University. "This flexibility may be key to understanding how water-rock interactions proceeded without erasing preexisting chemical differences within their parent asteroids." In general, materials with different compositions tend to be stable under different aqueous conditions.
However, laboratory experiments combined with previously published data on the solubility of M-S-H showed that M-S-H with different magnesium-to-silicon ratios can exist under similar aqueous conditions. The serpentine and saponite observed in the samples may also have formed from precursor M-S-H with corresponding compositions before transforming into these more crystalline minerals. Together, these results suggest a pathway by which different alteration minerals could form while preserving preexisting compositional differences from place to place.
M-S-H may therefore provide an important clue to understanding how these materials could be extensively altered yet remain chemically primitive. Reon Okumura et al., Pervasive poorly crystalline Mg-rich hydrous silicate material in C-type asteroid matrices, Communications Earth & Environment (2026). DOI: 10.1038/s43247-026-03958-2 Journal information: Communications Earth & Environment Swati Mestri holds a bachelor's degree in Electronics Engineering and has worked as a content editor since 2019.
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