The Cosmic Microwave Background (CMB) preserves a picture of the Universe as it was about 380 000 years after the Big Bang, and can reveal the initial conditions for the evolution of the Universe. Planck’s main objective is to measure the fluctuations of the CMB with an accuracy set by fundamental astrophysical limits. The spacecraft will chart the most accurate maps yet of the CMB.
Planck's instrument detectors are so sensitive that temperature variations of a few millionths of a degree will be distinguishable. This unrivalled sensitivity together with the large and smooth surface of its telescope and its unprecedented wavelength coverage make Planck the most sophisticated 'time machine' ever.
Planck's major objectives are:
To determine the large-scale properties of the Universe with high precision.
Planck will take a census of the main constituents of the Universe and build a history of their evolution in time. For example, it will accurately determine the density of normal matter, allowing us to calculate the total number of atoms in the visible Universe.
It will also investigate the nature and determine the amount of dark matter — a strange substance that does not emit or reflect electromagnetic radiation, but whose presence can be inferred from its gravitational pull on normal detectable matter, and which may account for around 90% of matter in today's Universe. Planck will also investigate the nature of dark energy, a form of energy that is theorised to account for the Universe's expansion at an accelerating rate.
To test theories of inflation, a period of extremely rapid expansion that gave birth to the Universe and that is the current explanation for some of its observed fundamental features. Planck's measurements will make it possible to study how and why such rapid expansion may have been triggered, how it evolved, and its consequences on our still-expanding Universe.
To search for primordial gravitational waves. These waves are expected to have been present at the time when inflation took place. Gravitational waves distort the fabric of space-time and carry information about the mechanism and the energies at which they were generated. Should Planck succeed in detecting these signatures, it would provide strong evidence for inflation.
To search for 'defects' in space, that would indicate that the Universe harboured local inhomogeneities in its very early phases. For instance, the presence of cosmic strings would hint at exotic physical phenomena that may have contributed to the origin and evolution of the structures that we see in the Universe today.
To study the origin of the structures we see in the Universe today.
Planck's accurate measurements of the variations in the microwave background provide a direct probe into the initial inhomogeneities that slowly grew into the largest structures that we see today: galaxies, clusters of galaxies, and ubiquitous large voids. Comparing the structure of the Universe then and now allows testing the very complex theories of structure formation. In addition, the photons of the microwave background can tell us the time and manner of formation of the first stars of our Universe.
To study our and other galaxies in the microwave.
Planck will study the Milky Way and map, for the first time, the large- scale distribution of cold dust along the spiral arms. It will also be the first to map, in detail and in 3D, the magnetic field which permeates the Milky Way. Beyond our own Galaxy, Planck will observe distant radio and dusty galaxies and investigate how they form stars. At larger scales, it will study near and distant clusters of galaxies and extract clues on how they formed and evolved.