A flexible, water-formed mineral material hiding in asteroid Ryugu may help explain a puzzle billions of years in the making: how rocks could be changed by water yet keep traces of the early solar system.
Ryugu and carbon-rich meteorites are called chemically primitive because they preserve much of the chemistry present when the solar system formed. At the same time, water altered many of their original minerals. Water can carry elements away or move them through rock, so scientists have wondered how these objects could undergo extensive change without losing their early chemical patterns.
A team led by Kanazawa University and The University of Tokyo examined samples using powerful X-rays at two large research facilities: KEK-PF and SPring-8. Their work, published in Communications Earth & Environment, found that a poorly crystalline material resembling magnesium silicate hydrate, or M-S-H, is widespread in Ryugu and carbonaceous meteorites. “Poorly crystalline” means its atoms do not form the neat, repeating structure seen in well-formed crystals.
Earlier interpretations had focused mainly on two water-altered minerals, serpentine and saponite. The new study suggests M-S-H was also an important part of the picture. Unlike a mineral with a narrow recipe, M-S-H can contain different proportions of magnesium and silicon. That range may have allowed it to form in varied parts of an asteroid without forcing those areas to share the same original chemistry.
The researchers tested this idea with laboratory experiments and information from earlier studies on how much M-S-H dissolves in water. Their results indicate that M-S-H with different magnesium-to-silicon ratios can remain stable under similar water conditions. They also propose that serpentine and saponite in the samples may have begun as M-S-H with matching compositions, then changed into more orderly minerals.
This offers a possible route through the apparent contradiction. Water could transform minerals, while M-S-H helped preserve chemical differences that were already present from one place to another. In that way, a rock could show clear signs of alteration and still retain a record of its beginnings.
The finding does not settle every question about how water moved through Ryugu’s parent asteroid or the meteorites’ parent bodies. But it gives researchers a material to include in future models of those processes, rather than focusing only on the better-known minerals. The study, by Reon Okumura and colleagues, points to the value of looking closely at materials that may be easy to overlook: in these ancient rocks, a less orderly mineral could help explain how the early solar system’s chemical history survived change.