The Pioneer 10 anomalous acceleration and Oort cloud comets

Anderson et al. [Phys. Rev. D 65 (2002) 082004] recently reported new evidence that both Pioneer 10 and 11 are experiencing nearly the same unmodeled anomalous acceleration directed toward the Sun. Numerous mechanisms, both internal and external to the spacecraft, have been proposed to explain this unmodeled acceleration. If we assume that the cause of the anomalous acceleration is (1) external to the spacecraft, (2) isotropic, and (3) acts on bodies of cometary mass, then it would imply that new comets are more tightly bound to the Sun than previously believed. Here we show that the implied higher binding energy is incompatible with the established evidence that the galactic tide is dominant in making Oort cloud comets observable. We conclude that one or more of these assumptions must be invalid.