Moon rocks are typically three billion years old or older. The difference arises because the Earth's mantle is still hot and therefor plastic, so that the surface is constantly being destroyed and rebuilt by tectonic processes. Similarly, Neptune is currently losing more heat than Uranus, indicating that the interior of Neptune is hotter than that of Uranus. The warm core of Neptune is believed to be responsible for Neptune's rather strong magnetic field. Heat Loss Mechanisms Conduction.
Heat is the random motion of atoms.
Collisions between atoms will transport this random motion. This is the least efficient of the major heat loss mechanisms, but in opaque rigid matter is the operative one. In a gravitational field, lighter fluids surrounded by heavier fluids are buoyant. Since planets tend to be hot in the center and cool at the surface, it can happen that hot, less dense fluids lie below cool, more dense fluids. In that case, the hot fluids will rise toward the surface of the planet, carrying heat with them.