Saturn Appears to Emit Heat as Infrared Radiation in Excess

Saturn appears to emit heat as infrared radiation in excess of the energy absorbed from sunlight and also the Kelvin-Helmholtz contraction. The most likely major cause of this excess heating is:

A) the condensing of helium into droplets that fall into the planet, releasing gravitational energy as heat.
B) the radioactive decay of naturally occurring isotopes in the atmosphere and interior of Saturn.
C) energy released from the continuous shrinking and condensation of this fluid planet.
D) remnant heat from the original formation of the planet.