Enceladus’s internal ocean could be maintained for billions of years by the heat generated by tidal forces within its very fragmented and porous core, suggests a model presented this week in Nature Astronomy. This tidal friction inside the unconsolidated rocky core can explain all the global properties of Enceladus observed by the Cassini spacecraft.

Cassini discovered that Enceladus, a moon of Saturn, possesses a global ocean fed by intense hydrothermal activity beneath its icy crust. Cassini measurements of water escaping from geysers at the south pole show that this ocean is salty and contains organic molecules. However, tidal forces within the ice are not sufficient to sustain this activity, and without an additional contribution the ocean would freeze in less than 30 million years.

Gael Choblet and colleagues explore the possibility that this additional heating comes from the effect of tidal forces acting on a highly fragmented, highly porous core with a state-of-the-art model constructed from Cassini observations. They find that enough heat is generated by the resulting hydrothermal activity to keep the ocean liquid for tens of millions to billions of years. They find that this heat is dissipated preferentially at the poles, which explains why the ice shell is thinner there.

The authors’ model suggests that an ocean has existed within Enceladus for a long time, possibly long enough to create the conditions to develop life, but future missions to Enceladus are required to provide additional constraints on the habitability of this ocean world.