The Earth's core is significantly hot, with temperatures around 5500K, primarily due to gravitational compression and internal heat generation processes. Unlike smaller celestial bodies, which may have cold cores due to insufficient gravity, the Earth's size ensures that its core remains hot. The heat is not solely residual from initial formation but is generated by processes such as radiogenic decay of heavy elements like uranium and thorium, as well as potassium-40 decay. Core-mantle friction may also contribute to this heat. The cooling of the Earth's core is a gradual process expected to occur over hundreds of millions of years. Geologists determine core temperatures through heat flow measurements, which indicate an average of about 100 milliwatts per square meter at the Earth's surface. In contrast, stars like the Sun can sustain thermonuclear fusion due to their massive size, which creates the necessary pressure and temperature in their cores.
