  Protons detected by the PAMELA experiment in the period 2006-2014 have been
analyzed in the energy range between 0.40-50 GV to explore possible
periodicities besides the well known solar undecennial modulation. An
unexpected clear and regular feature has been found at rigidities below 15 GV,
with a quasi-periodicity of $\sim$450 days. A possible Jovian origin of this
periodicity has been investigated in different ways. The results seem to favor
a small but not negligible contribution to cosmic rays from the Jovian
magnetosphere, even if other explanations cannot be excluded.
