Asked by: Harvey Turner, Jersey
It is probably not possible for a planet to be entirely liquid. This is because a planet needs to be ‘self-gravitating’ so that it holds its spherical shape under gravity. It thus requires a substantial amount of mass, which means the pressure and temperature in the inner regions are usually high. The difference between the interior and exterior means that matter cannot exist in a single state, and there will always be regions where the material is vapour or solid. However, it is possible for a planet to be entirely covered by liquid over a solid core.
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