Enceladus heats up because its core is like a sponge

mantle plumes seen on Earth, where hot upwellings drive material upwards, displacing cooler material that sinks toward the core. Any seafloor hotspot that generates power over 5GW is able to create a plume. Given a small enough core and high enough energy, these combine to create a web of upwellings across Enceladus’ interior. Heat also ends up concentrated under the poles, which may help explain why liquid water is closest to the surface there, powering its geysers.

As long as the power generated is above 15GW, it’s enough to keep Enceladus’ global ocean liquid for billions of years. No other sources of heat other than the gravity-driven tidal effects are required.

While it may be hard to imagine the core of an entire moon being fractured enough for any of this to work, Enceladus is relatively small and might not have formed in a way that generated enough heat to completely rework its core. Its radius, for example, is only half that of the dwarf planet Ceres in the asteroid belt. So there’s a chance that the core is something akin to a “rubble pile” that’s seen on smaller asteroids.

Nature Astronomy, 2017. DOI: 10.1038/s41550-017-0289-8  (About DOIs).

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