  Measurements of the cosmic microwave background (CMB) allow high precision
observation of the cosmic plasma at redshift z~1100. After the success of the
NASA satellite COBE, that in 1992 provided the first detection of the CMB
anisotropy, results from many ground-based and balloon-borne experiments have
showed a remarkable consistency between different results and provided
quantitative estimates of fundamental cosmological properties. During the
current year the team of the NASA WMAP satellite has released the first
improved full-sky maps of the CMB since COBE, leading to a deeper insight in
the origin and evolution of the Universe. The ESA satellite Planck, scheduled
for launch in 2007, is designed to provide the ultimate measurement of the CMB
temperature anisotropy over the full sky, with an accuracy that will be limited
only by astrophysical foregrounds, and robust detection of polarisation
anisotropy. Planck will observe the sky with two instruments over a wide
spectral band (the Low Frequency Instrument, based on coherent radiometers,
from 30 to 70 GHz and the High Frequency Instrument, based on bolometric
detectors, from 100 to 857 GHz). The mission performances will improve
dramatically the scientific return compared to WMAP. Furthermore the LFI
radiometers (as well as some of the HFI bolometers) are intrinsically sensitive
to polarisation so that by combining the data from different receivers it will
be possible to measure accurately the E mode and to detect the B mode of the
polarisation power spectrum. Planck sensitivity will offer also the possibility
to detect the non-Gaussianities imprinted in the CMB.
