CAN THE PIONEER ANOMALY BE INDUCED BY VELOCITY-DEPENDENT FORCES? TESTS IN THE OUTER REGIONS OF THE SOLAR SYSTEM WITH PLANETARY DYNAMICS

We analyze the impact of some velocity-dependent forces recently proposed to explain the Pioneer anomaly on the orbital motions of the outer planets of the solar system from Jupiter to Pluto, and compare their predictions ( secular variations of the longitude of perihelion pi or of the semimajor axis a and the eccentricity e) with the latest observational determinations by E. V. Pitjeva with the EPM2006 ephemerides. It turns out that while the predicted centennial shifts of a are so huge that they would have been easily detected for all planets with the exception of Neptune, the predicted anomalous precessions of pi are too small, with the exception of Jupiter, so that they are still compatible with the estimated corrections to the standard Newton-Einstein perihelion precessions. As a consequence, we are inclined to discard those extra forces predicting secular variations of a and e, also for some other reasons, and to give a chance, at least observationally, to those models yielding perihelion precessions. Of course, adequate theoretical foundations for them should be found.