Table of content:

 Primary fluctuations

 Secondary effects

 The Galaxy & the ISM

 Other scientific aspects of the Planck mission are still in construction.

This part is devoted to the scientific goals of the Planck mission. The main goal of the Planck mission is to measure the primary CMB fluctuations, that is the temperature fluctuations that arise from density fluctuations of the CMB emitting region itself (called the last scattering surface). These primary fluctuations are particularily useful to estimate the matter content of the universe and also to shed lights on the yet unknown mechanism which has generated these fluctuations much earlier in history of the universe. This is presented in heading Primary fluctuations.

In addition to these primary fluctuations, there are secondary sources of CMB anisotropies, which mainly come from interaction of CMB photons with cosmic structures. These anisotropies are called secondary both because they are usually not the dominant contribution to the observed anisotropies and because they cannot be computed “from first principles” in the sense that they exist only because of the presence of cosmic structure which form when the density fluctuations become large, so that a lot of astrophysical ingredients are in fact needed to understand these objects correctly. Various aspects of secondaries anisotropies is presented in heading Secondary effects.

Finally, when one tries to observe the furthest light of the universe (the CMB), one also sees everything that stands between us and the CMB emitting region. The solar system, the interstellar medium, our galaxy and other galaxies therefore act as foregrounds. If one is interested only in the primary and secondary fluctuations, these unwanted foregrounds are annoying and they are to be studied only to be better removed from the data so as to extract the CMB fluctuations as accurately as possible.However, these foregrounds can also be observed for themselves and their understanding is useful to many groups of astrophysicists. As a matter of fact, a mission such as Planck will obtain a lot of information about them. More on these foregrounds can be found in heading The Galaxy & the ISM.

One can find a complete overview of the scientific program of Planck in the so-called "Blue Book" (9MB pdf) issued at the end of 2004.