Diamond anvil experiments at 50 GPa show magma oceans dissolve hydrogen to form Earth-volume water

Experiments compressed synthetic peridotite with hydrogen under core-formation conditions, measuring hydroxyl incorporation via Raman and FTIR. Resulting D/H ratios fell within terrestrial mantle values, bypassing the mismatches recorded by Rosetta at 67P and by Hayabusa2 at Ryugu. Parallel JWST spectra of young rocky exoplanets show steam atmospheres consistent with outgassing rather than late veneer delivery.

Comet D/H ratios average 3-10 times VSMOW while carbonaceous chondrites reach only 0.7-1.5 times VSMOW; neither set reproduces Earth's bulk inventory without ad-hoc fractionation. The new solubility data indicate a 500-1000 km deep magma ocean can sequester and later degas enough hydrogen to yield 1-3 oceans of water, aligning with Hf-W chronology placing core formation before 30 Myr.

Operationally this reframes habitability metrics: planets need only sufficient primordial hydrogen and magma ocean duration, not specific impactor populations. Mission planning for Dragonfly and future ocean-world orbiters must now incorporate endogenous water budgets when interpreting surface chemistry.

Next measurements will come from the Europa Clipper MASPEX instrument, which can test whether plume volatiles match predicted mantle-derived D/H rather than chondritic ratios.