A ternary phase diagram for the system MgSiO₃–Fe–H₂ at T = 5318 K and P = 13.5 GPa. Regions of one-phase stability that lie outside of both the spinodal and binodal curves are shown in pale gray. Regions inside of the spinodals where two liquid phases are ensured are shown in darker gray. The binodals are shown by the blue curves, and coexisting phase compositions for a given bulk composition are shown by the tie lines connecting individual binodes. Regions of two-phase metastability are between the spinodals and binodals and shown in sky blue. Reference planet bulk compositions projected into this ternary space, in mole fractions, are shown for Earth (⊕), our fiducial sub-Neptune , and Neptune , with the weight fractions of H₂ being 0.17%, 2%, and 20%, respectively.