Normally, the core part of a planet is scorching hot.
Not only is most of the initial energy of the planet sealed within the core, but during the early solidification stage of the planet, the hot molten material generated inside the planet will shift towards the core under the influence of gravity and penetration effects. If it is a rock-based planet, the radioactive materials accumulated near the core can usually reach a concentration millions of times that of the surface. In such an environment, a highly radioactive core is almost equivalent to a slow ongoing nuclear reaction in a thermal power plant, and this heat cannot be vented, ultimately heating the core into a scorching liquid metal ball: under astonishing pressure and temperature, even diamonds will become as soft as butter, and no matter how high the temperature is, the material can only liquefy here, but cannot vaporize.
This is the regular version of the core.
