Thermal radiation may account for Pioneer anomaly

Space.com : The Pioneer anomaly, which caused deep space probes Pioneer 10 and 11 to slow down on their paths away from the sun may be solved. NASA first noted the anomaly 30 years ago. The broader scientific community began investigating it in 1998, and a host of reasons for the slow-down have been proposed, among them gravitational forces from the Kuiper belt, dark matter, or some other unidentified source; drag from the interplanetary medium; and radiation pressure, including thermal radiation from the heat of the probes themselves. Orfeu Bertolami, of the University of Porto in Portugal and colleagues created three-dimensional simulations of how thermal radiation emitted by the deep space probes bounces off their surfaces. They found that when the reflected heat was added into prior calculations of thermal effects, thermal radiation accounts for all of the anomaly, rather than the 66% previously supposed.