Following the recent emergence of the ESA Rosetta mission from its 2.5-year deep-space hibernation, the first new data from the on-board Standard Radiation Environment Monitor (SREM) instrument have been received, The attached figure shows the charged particle count rates observed in two energy channels of the SREM: TC3, which is sensitive to protons from roughly 27 MeV energy upward, and TC2 from 49 MeV on. The counts observed give an indication of the Galactic Cosmic Ray (GCR) environment encountered by Rosetta at its current location at 4.4 AU distance from the Sun. These new measurements take place during a solar maximum period and are a factor ~2 lower than in February 2011 which was during the previous solar minimum. This is as expected by the variation of the GCR fluxes over the 11-year solar cycle. Similar behaviour can be observed by another SREM unit on the ESA Integral spacecraft ("IREM") at 1 AU, showing the good agreement between the different SREM units. The spikes seen in the Integral diagram result from the periodical passage of the spacecraft through the Earth's radiation belts, while the periods in between correspond to the interplanetary space.
Plots courtesy of P. Buehler