Laboratory Decompression of Metastable Salt-Bearing Ice VII Expels Sodium Chloride at 5.1 GPa
What Was Observed (Empirical Data)
Using synchrotron X-ray diffraction and neutron diffraction, researchers observed that a quenched amorphous sodium chloride solution crystallized into a metastable ice VII lattice exhibiting an 8.5% unit-cell volume expansion without detectable crystalline halite. Ab initio calculations confirmed that ionic substitution of water molecules by sodium and chloride ions reproduces this structural expansion. Upon decompression at 300 K, the synthesized phase expelled crystalline sodium chloride at 5.1 ± 0.3 GPa without reforming during recompression.
The Reality Check (Anti-Hype Analysis)
These findings represent high-pressure laboratory experiments and computational models rather than in situ measurements of any planetary mantle. The observed salt-bearing ice VII is strictly metastable and requires rapid pre-quenching into an amorphous state, a pathway that may not reflect natural planetary accretion or convective conditions. Consequently, the proposed 5.1 GPa compositional boundary remains a theoretical transport mechanism rather than confirmed evidence of exoplanetary ocean dynamics.
PRIMARY SOURCE:
arXiv Astrophysics (astro-ph)