Pioneer Anomaly is Fading

The Pioneer anomaly is a tiny, unexplained deceleration of the Pioneer 10 and 11 spacecraft, which are now at the edge of the Solar System. A 19 August report in Physical Review Letters describes an arduous, multi-year effort to accurately define the anomaly by gathering and analyzing all available tracking data for the two probes. The analysis shows that the anomaly is not constant, as researchers had believed, but is decreasing with time. The finding points toward a conventional explanation of the phenomenon, most likely asymmetric radiation of heat, and against some of the more exotic proposals.