ESA Science & Technology - Objectives

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