The Planck milestone

Planck, a European Space Agency satellite to be launched in 2007, is dedicated to surveying the full sky at sub-millimetre and millimetre wavelength. The primary goal of the mission is the final mapping of the Cosmic Microwave Background Anisotropies (CMBA). With an angular resolution of 5 arcmin and a sensitivity of ΔT_CMB/T_CMB=2×10⁻⁶, the Planck mission will be about 1000 times more sensitive than COBE-DMR and at least 20 times more than WMAP. Planck has also very good capabilites for measurements of polarization, although it will not exhaust the information contained in the CMBA polarization pattern. Two instruments share the Planck focal plane; the High Frequency Instrument (HFI) covers the wavelength ranging from 300 μm to 3 mm by using 48 bolometers cooled to 100 mK. This instrument is realized by an international collaboration, led by the IAS at Orsay. The other part of the relevant electromagnetic spectrum is covered by the Low Frequency Instrument (LFI) using HEMT radiometers cooled at 18 K and realized by a consortium led by the CNR in Milano. The first part of this article presents expected results of Planck on CMBA, both in intensity and polarization. In a second part, the global design of the Planck mission will be presented. We describe in particular the implications of Planck scientific goals on the instruments design, and especially on HFI that is the most sensitive Planck instrument. To cite this article: F.R. Bouchet et al., C. R. Physique 4 (2003).