Your News Feature 'The test of inflation' (Nature 458, 820–824; 2009) highlights some of the exciting scientific data to be collected by the European Space Agency's Planck spacecraft, and the theoretical issues underlying its objectives to study the moments after the Big Bang.
You discuss the new high-frequency 52-bolometer detector, but do not mention the 22-radiometer low-frequency instrument (LFI). However, it is this unique combination of Planck radiometers and bolometers in an integrated focal assembly that is key to achieving the broad spectral coverage needed to separate foreground emission of galactic and extragalactic origin from the cosmological signal.
This feature is essential in searching for subtle signatures in the cosmic microwave background, including possible clues from an inflationary era of the Universe (such as polarization B-modes and non-Gaussianity). Planck's 70-gigahertz radiometers will observe the sky in the frequency band that is least contaminated by foregrounds, and with a sensitivity and angular resolution surpassing that of all previous experiments.
Following the 1989 Cosmic Background Explorer differential microwave radiometer and the 2001 Wilkinson microwave anisotropy probe, the Planck radiometric instrument will use polarization-sensitive detectors based on indium phosphide HEMT (high electron-mobility transistor) cryogenic amplifiers cooled to 20 K. It is the data from these detectors, combined with the bolometer data, that will give Planck its superiority over its predecessors.