A research team from Kanazawa University and The University of Tokyo solved a long-standing puzzle in cosmochemistry: how asteroid Ryugu and carbonaceous meteorites could undergo extensive water reactions while still preserving the chemical composition of the early solar system.
Using synchrotron X-ray facilities at KEK-PF and SPring-8, the researchers examined these extraterrestrial materials and identified a previously overlooked component called poorly crystalline magnesium silicate hydrate (M-S-H). This material is widespread in Ryugu samples 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."
The conventional understanding focused on serpentine and saponite minerals formed during aqueous alteration. The new work using synchrotron-based soft X-ray absorption spectroscopy revealed that M-S-H, with its variable composition ratios, could exist under similar aqueous conditions. This flexibility allowed different alteration minerals to form while maintaining compositional differences from place to place within the asteroids.
Laboratory experiments and published solubility data showed that serpentine and saponite may have formed from precursor M-S-H before transforming into these more crystalline minerals. This pathway explains how extensive water alteration could occur without erasing the primitive chemical signatures preserved in these ancient materials.
The findings appear in Communications Earth & Environment.