The Pioneer Anomaly is the effect seen in the paths of the Pioneer and Voyager spacecraft as they traveled out of the Solar System. An unknown force appears to be acting on them and causing them to deviate ever so slightly from their designed trajectories. This is not news, but a new study on other craft has revealed the same effect may have moved Galileo, NEAR, Rosetta, Cassini and the recent MESSENGER mission to Mercury.
Space.com has the full story and interviewed John Anderson, who performed the study. Anderson said, amongst other things, that he thought it likely that this was connected to the Pioneer Anomaly and suggested a couple of possible causes of the anomaly.
The question remains as to whether this is new physics or some problem in the way in which such objects are modelled as they move through deep space.
I did a talk on the Pioneer Anomaly last year. If you’re interested you can download the PowerPoint file here. It contains references for further reading.