The European Space Agency Gaia mission: exploring the Galaxy

The Gaia astrometric mission is one of the next two cornerstones of the European Space Agency's science program.
It was approved in 2000 and the launch is foreseen by August 2012. Gaia will continuously scan the entire sky for five
years, yielding positional and velocity measurements with the
accuracies needed to produce a stereoscopic and kinematic census of about one billion stars throughout our Galaxy and beyond, i.e., about 1% of the galactic stellar population. Gaia's main scientific goal is to quantify early formation and the subsequent
dynamic and chemical evolution of the Milky Way and its history of star formation. It will provide insight into questions
such as: When did the stars in our Galaxy form? When and
how was it assembled? What is the distribution of dark matter? The stellar survey will have a completeness to V = 20 mag, with
an accuracy of about 20 µas at 15 mag. The astrometric information
will be combined with astrophysical data acquired
through on-board spectrophotometry and spectroscopy, allowing
the chemical composition and age of the stars to be
derived. In addition, Gaia will observe tens of thousands of extra-solar planetary systems, some 10⁵10⁶ minor bodies in our solar system, millions of galaxies in the nearby universe, and some 500,000 distant quasars. It will also provide a number of stringent new tests of general relativity and cosmology. Data
acquired and processed as a result of the Gaia mission are estimated
to amount to about 1 petabyte. The challenging problem is the close relationship between astrometric and astrophysical data, which involves a global iterative solution that updates instruments parameters, the attitude of the satellite,
and the properties of the observed objects. The Data Processing and Analysis Consortium is a joint European effort in charge of preparation and execution of data processing.