Eli5: How does the core of the Earth (or any planets) not cool and still give off tons of heat energy? Where is this energy coming from?

Question

Eli5: How does the core of the Earth (or any planets) not cool and still give off tons of heat energy? Where is this energy coming from?

In: 202

Answer 1

The core is 19,400,000,000,000,000,000,000,000 kilograms. That does cool down if you give it a few billion years.