Planck has provided a map of the Cosmic Microwave Background (CMB) field at high angular resolution, covering at least 95% of the sky over a wide frequency range. Planck has been designed to have ten times better sensitivity to temperature variations of the CMB and more than fifty times the angular resolution of the Cosmic Background Explorer (COBE) spacecraft.
The simultaneous mapping of the sky over a wide frequency range has permitted scientists to separate Galactic and extragalactic foreground radiation from the primordial cosmological background signal. Planck has provided vastly improved performances compared to balloon-borne and ground-based experiments and has exceeded the performance of other space-based instruments. The spacecraft revolved about its Sun-pointing axis once per minute to gyroscopically stabilise its attitude. Planck used this stabilisation spin to operate in a sky-scanning survey mode, observing at least 95% of the sky on two separate occasions within twelve months.
The key objectives of Planck are as follows:
- Measurement of CMB anisotropies with a temperature resolution (ΔT/T) of the order of 10-6 (astrophysical limit set by small scale fluctuations in foreground emission) at all angular resolutions greater than 10 arcminutes - this allows scinetists to determine fundamental parameters such as the spatial curvature of the Universe, the Hubble constant H0 and the baryon density to a precision of a few percent
- Tests of inflationary models of the early Universe - specifically the determination of the spectral index of the primordial fluctuation spectrum to high precision and the possible detection of a component of the CMB anisotropies induced by primordial gravitational waves, which would show conclusively that the Universe passed through an inflationary phase
- Detection of characteristic signatures in the CMB created by topological defects, such as cosmic strings and textures, generated at a phase transition in the early Universe
- Measurement, with greatly improved accuracy, of the amplitudes of structures in the CMB with physical scales between 100 and 1000 h-1Mpc, that have sizes comparable to the voids and filaments observed in the galaxy distribution today - by comparing these Planck measurements with new redshift surveys of around 106 galaxies it will be possible to establish a consistent theory of the formation of cosmic structure and shed light on the nature of the dark matter that dominates the present Universe
- Measurements of the Sunyaev-Zeldovich effect - temperature anisotropies that are due to the frequency change of microwave background photons undergoing inverse Compton scattering by hot electrons in the gaseous atmospheres of rich clusters of galaxies - Planck can detect this effect in many thousands of rich clusters, providing information on the physical state of the intracluster gas and on the evolution of rich clusters - these measurements can also be combined with spatially resolved X-ray observations to estimate the Hubble constant H0
- Using the high sensitivity of Planck's sub-millimetre bolometer channels, it is possible to disentangle the frequency dependent Sunyaev-Zeldovich effect in rich clusters of galaxies from temperature differences caused by their peculiar motions - it should be possible to measure peculiar velocities for more than 1000 clusters to an accuracy of around 250 kms-1, providing powerful tests of theories of structure formation and information on the mean mass density of the Universe