Planck is designed to image the anisotropies of the Cosmic Microwave
Background (CMB) over the whole sky, with unprecedented sensitivity (ΔT/T ~ 2 × 10-6) and angular resolution (~5 arcmin). Planck
will provide a major source of information relevant to several cosmological
and astrophysical issues, such as testing theories of the early universe and
the origin of cosmic structure. The ability to measure to high accuracy the
angular power spectrum of the CMB fluctuations will allow the determination of
fundamental cosmological parameters with an uncertainty of order a few
percent. In addition to the main cosmological goals of the mission, the Planck
sky survey will be used to study in detail the very sources of emission which
“contaminate” the signal due to the CMB. This will result in a wealth of
information on the properties of extragalactic sources, and on the dust and
gas in our own galaxy. One specific notable result will be the measurement of
the polarized emission from our own Galaxy. The ability of Planck to measure
polarization across a wide frequency range (30–350 GHz), with high precision
and accuracy, and over the whole sky, will provide unique insight into the
properties of the interstellar medium. An overview is presented of the Planck
mission, its scientific objectives, the key elements of its technical design,
and its current status.