What mechanism might maintain liquid water oceans subsurface on worlds like Europa or Enceladus, far outside the traditional Habitable Zone?

Answer

Tidal kneading from their giant host planets.

Worlds situated far outside the traditional HZ can possess subsurface liquid oceans warmed by internal heating generated through powerful tidal forces exerted by massive neighboring planets.

What mechanism might maintain liquid water oceans subsurface on worlds like Europa or Enceladus, far outside the traditional Habitable Zone?

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What Is the Habitable Zone? - YouTube

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