The Pioneer Anomaly – solved?
Over the years, a great many ideas have been suggested, from the mundane to the exotic. Some like the suggestion that there was a flaw Einsteins theories on gravitation, which remains our best fit, seemed to be grasping at straws since they ignored the fact that the anomaly was unique to these two spacecraft. Other scientists suggested that the measurements themselves could be suspect. One idea, which was rejected early on, was that infra-red radiation from the craft’s own internal heat (generated mainly by the radio-isotope power supply) could exert a tiny amount of radiation pressure, which would cause a tiny amount of thrust of about the same magnitude as observed.
What Francisco’s team did was to revisit this last idea, using a novel approach. In order to properly model the emissions of infra-red light, they used a technique from the world of computer graphics: Phong Shading. Developed by Dr Bui Tuong Phong in 1970, this technique has become a standard in graphical rendering software to accurately model light reflecting from curved surfaces so as to draw realistic shading. When Phong Shading was applied to 3D computer representations of Pioneer 10 and Pioneer 11, Francisco got a very accurate model of the infra-red emissions. With this new data they were able to show that the radiation pressure from the emitted heat, plus the pressure from that same heat reflecting from large surfaces (like the antenna dish) could accurately account for the anomalous acceleration.
An impressively novel way to use unusual tools to solve an old problem! The paper describing their work can be downloaded and read here: