Schematic view of the relative size and internal structure of Pluto and Enceladus, both with proposed rocky cores, liquid water oceans, capping hydrate, and an ice layer. For Enceladus, we also illustrate the subsurface shallow reservoirs of liquid water proposed by Matson et al. (2018). For Pluto, we illustrate the structure with the thermally-insulating layer of CO₂ hydrate, similar to the methane hydrate layer proposed by Kamata et al. (2019).