[inkcapmushroom]

I'm no geologist but I would think it would be hard for the outer layer to stay stable enough to harden to that degree, while the inner part is still liquid and cooling. On our own planet the crust is incredibly thin compared to the other layers, even while the mantle is cooled enough to be solid, and the solid mantle still moves around enough to break apart the crust constantly. Seems impossible for the hollow eggshell of the crust to not break and crumble into the retreating center at some point.