Establish the physical mechanism of hydrogen–silicate core–envelope intermingling

Establish the physical processes that produce intermingling between hydrogen-rich planetary envelopes and molten silicate-rich cores, including whether convective surface renewal provides a sufficient intrinsic mechanism for hydrogen incorporation during planetary growth.

Background

The paper identifies the formation of hydrogen-rich molten cores beneath hydrogen-rich envelopes as an important unresolved issue in sub-Neptune evolution. Earlier work establishes strong chemical-potential driving forces for hydrogen dissolution and indicates that silicate, iron, and hydrogen may become fully miscible at relevant pressures and temperatures, but it does not establish how hydrogen is physically transported and mixed into the molten core.

The paper investigates convective surface renewal as a candidate mechanism: cooling-driven convection repeatedly replaces hydrogen-enriched surface melt with fresh interior melt, allowing continued diffusive transfer across the core–envelope interface despite stabilizing compositional buoyancy. Because the paper presents this mechanism as plausible rather than as a definitive resolution of all physical processes leading to core–envelope intermingling, the broader mechanism remains explicitly identified as unsettled.