  Protons and helium nuclei are the most abundant components of the cosmic
radiation. Precise measurements of their fluxes are needed to understand the
acceleration and subsequent propagation of cosmic rays in the Galaxy. We report
precision measurements of the proton and helium spectra in the rigidity range 1
GV-1.2 TV performed by the satellite-borne experiment PAMELA. We find that the
spectral shapes of these two species are different and cannot be well described
by a single power law. These data challenge the current paradigm of cosmic-ray
acceleration in supernova remnants followed by diffusive propagation in the
Galaxy. More complex processes of acceleration and propagation of cosmic rays
are required to explain the spectral structures observed in our data.

High Energy Astrophysical Phenomena