  Analysis of the radio tracking data from the Pioneer 10/11 spacecraft at
distances between about 20 - 70 AU from the Sun has consistently indicated the
presence of an unmodeled, small, constant, Doppler blue shift drift of order 6
\times 10^{-9} Hz/s. After accounting for systematics, this drift can be
interpreted as a constant acceleration of a_P= (8.74 \pm 1.33) \times 10^{-8}
cm/s^2 directed towards the Sun, or perhaps as a time acceleration of a_t =
(2.92 \pm 0.44)\times 10^{-18} s/s^2. Although it is suspected that there is a
systematic origin to this anomaly, none has been unambiguously demonstrated. We
review the current status of the anomaly, and then point out how the analysis
of early data, which was never analyzed in detail, could allow a more clear
understanding of the origin of the anomaly, be it a systematic or a
manifestation of unsuspected physics.
