The unusual trajectories of the Pioneer 10 and 11 spacecraft as they leave the solar system are not caused by any exotic new physics but by mundane thermal emissions powered by radioactive decay. That is the verdict of researchers in the US and Canada, who have compared the results of an extremely detailed computer simulation of the thermal forces on one of the craft with the same forces calculated from the trajectory of the mission. The study also suggests that the observed reduction of the extra acceleration over time is the result of how electricity is generated on board the spacecraft and distributed to its scientific instruments.

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