Transcript: In the 1960s scientists were surprised to find that Jupiter emits twice as much infrared radiation as it receives from the Sun. We see Jupiter in the reflected light of the Sun, and since no planet is a perfect reflector, like a mirror, we must receive less visible radiation from a planet then is received by that planet from the Sun. The same must be true of heat as well, yet in Jupiter's case the planet is emitting more infrared radiation then it receives from the Sun. The answer must be an unanticipated heat source within Jupiter. The answer to the puzzle is the fact that Jupiter is still contracting slightly. The contraction leads to the conversion of gravitational potential energy into thermal energy which is then radiated into space as infrared waves.