Why do Jupiter and Saturn emit more heat than they receive from the Sun?

Jupiter and Saturn are giant planets with enormous internal energy stores. They formed by rapidly accumulating gas and rock, and as they slowly contracted under gravity, they converted gravitational energy into heat. Jupiter’s deep interior still leaks that ancient heat into space, while Saturn appears to have an additional energy source from helium separating from hydrogen and raining downward. This extra internal heating explains why these planets glow in infrared even though they are far from the Sun.