DIFFUSION HEAT transfer is due to RANDOM molecular motion. Neighboring molecules move randomly and transfer energy between one another - however there is no bulk motion. RADIATION heat transfer, on the other hand, is the transport of heat energy by electromagnetic waves. All bodies emit thermal radiation.

In particular, notice that unlike diffusion, radiation heat transfer does not require a medium and is THUS the only mode of heat transfer in space. The time scale for radioactive heat transfer is much smaller than diffusive heat transfer.

Diffusion heat transfer is due to random molecular motion. Neighboring molecules move randomly and transfer energy between one another - however there is no bulk motion. Radiation heat transfer, on the other hand, is the transport of heat energy by electromagnetic waves. All bodies emit thermal radiation.

In particular, notice that unlike diffusion, radiation heat transfer does not require a medium and is thus the only mode of heat transfer in space. The time scale for radioactive heat transfer is much smaller than diffusive heat transfer.