J. Geophys. Res. http://doi.org/nsh (2013)
The geologically active surface of Enceladus indicates that this icy moon of Saturn is differentiated into a rocky core, an icy mantle and possibly an internal ocean; however, the moon's shape is inconsistent with differentiation. Mathematical analyses suggest that a modestly flattened and distorted core can explain the global shape of Enceladus.
William McKinnon at Washington University in St Louis, USA, used a mathematical model to quantitatively assess the hypothesis that the core of Enceladus is topographically lumpy. Core irregularity would alter Enceladus's global geoid and therefore the dimensions of its axes, assuming Enceladus is in hydrostatic equilibrium. He finds that the amount of excess topography that is required to explain the moon's shape is only about 10 km for a core with a radius of 160 km. The model predictions can be tested by measuring the gravity field of Enceladus.
A suitably irregular core would affect the tidal heating of the icy mantle and allow an internal ocean to remain unfrozen near the south pole of Enceladus, potentially explaining the concentration of geological activity at high southern latitudes.
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Goldin, T. Wonky to the core. Nature Geosci 6, 805 (2013). https://doi.org/10.1038/ngeo1979