Liquid core has little to do with gravitation, rather the magnetic field.
Actually, that'd be an issue for terraforming as well, since it's fairly important in not getting irradiated.
The artificial gravity system seems convoluted from a thermodynamic standpoint, since to provide energy to a system that moved high-density material at large fractions of c around you'd need to have a load of fuel on hand. Assuming it's fusion or some other conventionally predictable process, all the mass and energy would be already present...
We need more Aika/Al romance if only they would let him talk technobabble