Planck and the Cosmic Microwave Background

The European Planck surveyor satellite will map the entire sky at microwave wavelengths - why is this important? Scientist will be able to scrutinize models which explain the formation of galaxies by measuring fluctuations in the distribution of dark matter, only a mere 300 000 years after the big bang. These fluctuations manifest themselves as small variations of the mean sky temperature of 3 degrees Kelvin and have been generated when the first atoms were formed in cosmic history. From these seed fluctuations larger and larger objects were assembled by gravity which finally resulted in the formation of galaxies and clusters of galaxies. Important cosmological parameters are the amplitude of these seed fluctuations and the mean density of matter, which Planck will be able to measure.


A large part of the scientific programme is devoted to so-called secondary anisotropies: these are fluctuations of the sky temperature which are generated by the interaction of photons of the microwave background with the large-scale distribution of galaxies. There are basically two categories of interactions: gravitational lensing, which can be used for precision measurements of cosmological parameters, and Compton-interactions with electrons of the hot gas inside clusters of galaxies - a potential new powerful way of detecting clusters of galaxies.

Planck's advantage over previous experiments is its high sensitivity and angular resolution: it can measure fluctuations of a few microKelvin, and its angular resolution is better than a tenth of a degree. The survey will be carried out from the Lagrange-point L2, at roughly 1.5 million kilometers from Earth - 5 times the mean Earth-Moon distance. The science team of Planck comprises about 500 scientists who are anxious to see the satellite launched on 14 May 2009, after 15 years of preparation.

Written by Bjoern Malte Schaefer
Appeared in the Italian translation on Il Denaro, 14.05.2009

Image: map of the microwave sky as observed by NASA's satellite WMAP, launched in 2001. Different colours represent the tiny fluctuations in temperature: the difference between red and blue spots is only 0.0002 degrees. Planck's maps will be even more precise than that. Credits: NASA/WMAP team.