Pioneer slowing anomaly caused by thermally-induced infra-red photon thrust

The mysterious slight slowing of the NASA Pioneer 10 and 11 space probes which were launched in hte early 1970s has been explained.  According to the scientists at JPL (Jet Propulsion Labororatory in Pasadena) reporting in Physical Review Letters, the slight decelerration can be traced to a heating effect from the now distant space probes' power systems.  The scientists describe the effect as being anagolous to thrust being caused by photons from a light souce. In this instance it is the thermally induced emission of infra-red photons that is causing the deceleration.