Jupiter, Saturn, and Neptune radiate more energy into space than they receive from the Sun. What is the source of the additional energy?

The additional energy radiated by gas giant planets like Jupiter, Saturn, and Neptune, beyond what they receive from the Sun, primarily comes from their internal heat sources. These planets possess substantial amounts of internal heat, which are remnants from their formation and subsequent processes. Here's a breakdown of the sources of this internal heat:

Gravitational Contraction: During the formation of these planets from the primordial solar nebula, gravitational forces caused the gas and dust to collapse, leading to the compression of material. This gravitational contraction releases heat energy as potential energy is converted into thermal energy. Over billions of years, the heat generated by this process has contributed to the internal temperatures of these planets.
Differentiation and Core Heating: The process of planetary differentiation, where denser materials sink towards the center while lighter materials rise towards the surface, also generates heat. The energy released during this process helps to heat up the interiors of these planets. Additionally, the presence of metallic hydrogen in the cores of Jupiter and Saturn, and possibly in Neptune, generates heat due to the pressure exerted by the overlying layers.
Radioactive Decay: Radioactive elements present within the rocky cores of these planets contribute to their internal heat budget. The decay of radioactive isotopes such as uranium, thorium, and potassium releases heat energy as a byproduct, which adds to the overall internal heat of the planet.
Fluid Dynamics and Atmospheric Processes: Internal heat also drives fluid dynamics within the planets, such as convective motion in their atmospheres and the generation of powerful storms and weather patterns. These processes release additional heat into the atmosphere, which is eventually radiated into space.