Saturn's Ocean Moon Was Hiding in Plain Sight

> Rhoden: […] Some ocean moons even have low enough densities that they probably have water ice mixed into the rock in their interiors. With heat, that water ice melts into liquid water, which will erode rock to create salt water. […]

> Hall: Given how cold it is in the outer solar system, what generates the heat?

If you haven’t read the article yet, take a guess! Amazing. (Though I don’t know how well Rhoden’s explanation is supported or what other explanations might suffice.)