More surprises from PAMELA


The PAMELA satellite has been launched in 2006 and since then it has held many surprises. Back in 2008, the PAMELA collaboration found an anomalous cosmic positron abundance, which prompted the publication of hundreds of papers (690 citations to the original paper as of March 8, 2011). 
Last week, the collaboration has published on ‘Science Express‘ the measurement of proton and Helium spectra in the rigidity range 1 GV – 1.2 TV (see figure above). The shape of these spectra deviate significantly from the simple power-law behavior predicted by the current paradigm (see e.g. this review paper), which posits that cosmic rays in this energy range are accelerated in supernova remnants. 

Interestingly, the deviations from the predictions are different from protons and He nuclei, a feature that is difficult to accomodate even in the most sophisticated models of acceleration. 
In short, this means that we are probably seeing the effect of new sources of cosmic rays (in the paper the authors cite e.g. this study of a multi-component population of cosmic rays).