Planck’s cooling system (at 1 degree Kelvin)

To achieve the mission goals, the Planck instruments – the Low Frequency Instrument (LFI) and the High Frequency Instrument (HFI) - will operate at a few degrees above absolute zero. To achieve this, a series of cooling stages are required.

The picture shows the third and last cooling stage, bringing down the temperature of the bolometers in HFI down to 0.1 K.