Thermal and radiation environment of Planck. Vertical lines indicate boundaries between Surveys. Top panel: cosmic ray flux as measured by the onboard SREM; its decrease over time is due to the corresponding increase in solar activity, indicated by the sunspot number⁵. Solar flares show up as spikes in the proton flux. Second and third panels: temperature variation at two representative locations in the room-temperature SVM, i.e., on one of the (HFI) helium tanks and on one of the LFI back-end modules (BEMs). The sine-wave modulation tracks the variation of distance from the Sun. Bottom panel: temperature evolution of VG3, the coldest of three V-grooves, to which the sorption cooler is heat-sunk. The disturbances on the curve are due to adjustments of the operational parameters of this cooler.