I may be wrong, but insolation probably isn't a substantial factor in keeping cores molten because of how small the energy input is. Venus does have extremely a

I may be wrong, but insolation probably isn't a substantial factor in keeping cores molten because of how small the energy input is. Venus does have extremely active volcanoes. There's suspicion that it might have a stronger magnetic field if it were spinning faster (it's rotational period is currently longer than its year).