Superionic Helium in Mg₂SiO₄He₂ at Ultrahigh Pressure: Implications for Delayed Cooling of Hot Jupiters

Existing explanations invoke physical heating or delayed cooling through enhanced atmospheric opacity or inhibited convection, yet the possible role of reactions between volatiles and silicates under extreme conditions has received little attention. Here we predict a previously unknown compound, Mg₂SiO₄He₂, that becomes thermodynamically stable above 577 GPa, exhibits superionic helium diffusion at high temperature, and has thermal conductivity approximately one-quarter that of Mg₂SiO₄.

Its formation at hot Jupiter core-mantle boundaries sequesters helium into the silicate, creating a compositionally stratified, insulating thermal boundary layer that delays planetary cooling, a chemical mechanism complementing existing models of radius inflation. Our results provide new constraints on the chemical environment and thermal evolution of giant exoplanetary interiors.</p><p><br></p>