Located in the focal plane of the telescope, Planck’s Low Frequency Instrument (LFI), and the High Frequency Instrument (HFI), are equipped with a total of 74 detectors covering nine frequency channels. These detectors must be cooled to temperatures around or below 20 Kelvin so that their heat does not swamp the faint microwave signals they are designed to detect. Credit: ESA/AOES Medialab)