The essential difference between the models of Schmidt et al. (2011) and Greenberg et al. (1999) concerns where and how melting occurs within icy satellites like Europa. Greenberg et al. (1999) propose that tidal flexing causes frictional heating in the ice shell, generating local melting and the formation of subsurface water pockets near the surface. In contrast, Schmidt et al. (2011) argue that melting primarily occurs at the ice-ocean interface at the base of the shell due to thermal and compositional convection rather than near-surface tidal heating. Schmidt et al. (2011) dismiss the Greenberg et al. (1999) mechanism because their thermal modeling shows that tidal heating is insufficient to generate the required near-surface melting; instead, heat flow and melting are concentrated at the shell's base. This fundamental reasoning leads Schmidt et al. to favor basal melting over near-surface melt pockets.