Jupiter's internal heat source:

* Gravitational compression: Jupiter's massive size generates immense pressure and heat in its core.

* Helium rain: Jupiter's atmosphere is rich in helium, which condenses and falls towards the core, releasing heat.

Saturn's internal heat source:

* Gravitational compression: Saturn is less massive than Jupiter, resulting in lower internal pressure and heat.

* Helium rain: Saturn also experiences helium rain, but its process is less efficient than Jupiter's.

Temperature differences:

* Jupiter's core temperature: Estimated to be around 24,000°C (43,000°F).

* Saturn's core temperature: Estimated to be around 11,700°C (21,100°F).

Surface temperature:

* Jupiter's average temperature: -145°C (-234°F).

* Saturn's average temperature: -178°C (-288°F).

Conclusion:

Jupiter's greater mass and more efficient internal heat source make it significantly hotter than Saturn, both in terms of core temperature and overall internal heat. However, both planets have extremely low surface temperatures due to their distance from the sun.