Yeah, but Mars started with a molten core. Any planet without a molten core has no magnetic field, and will get its atmosphere stripped by solar winds.
100bit, there is no way to make that without melting the whole planet if ambient heat is enabled. It would also get rid of everything in the center besides the GPMP. I hope you understand. Also, not all planets have molten cores, take mars for example.
not very realistic, there is no molten core