The planet Saturn generates more heat than it receives from the Sun.
It has lost the heat caused by its formation, but helium drops “rain” down from the atmosphere, mostly hydrogen, which creates heat.
The droplets of helium releasing heat by friction as they fall down through the lighter hydrogen.
The cloud-top temperature ranges around –300°F (-200°C).
However, most of the extra energy is generated by the Kelvin-Helmholtz mechanism, which is slow gravitational compression.