PX282 - K3 - internal heat

all giants have thermal emission temperatures (effective temperatures) higher than their equilibrium temperatures

this implies additional sources of internal heat

jupiter can be heated from the gravitational potential energy left over from formation as it is slow to cool due to its large size

saturn and jupiter have ongoing differentiation from He rain, releasing gravitational potential energy, which is supported by an under-abundance of He in their atmospheres

neptune probably also has ongoing differentiation of metals/rocks

uranus does not have a significant excess heat, which is a mystery