GAIA: composition, formation and evolution of the Galaxy

Abstract

The GAIA astrometric mission has recently been approved as one of the next two \cornerstones' ofESA's science programme, with a launch date target of not later than mid-2012. GAIA will provide positionaland radial velocity measurements with the accuracies needed to produce a stereoscopic and kinematic census ofabout one billion stars throughout our Galaxy (and into the Local Group), amounting to about 1 percent of theGalactic stellar population. GAIA's main scienti c goal is to clarify the origin and history of our Galaxy, froma quantitative census of the stellar populations. It will advance questions such as when the stars in our Galaxyformed, when and how it was assembled, and its distribution of dark matter. The survey aims for completenesstoV= 20 mag, with accuracies of about 10 as at 15 mag. Combined with astrophysical information for eachstar, provided by on-board multi-colour photometry and (limited) spectroscopy, these data will have the precisionnecessary to quantify the early formation, and subsequent dynamical, chemical and star formation evolution ofour Galaxy. Additional products include detection and orbital classi cation of tens of thousands of extra-Solarplanetary systems, and a comprehensive survey of some 105−106minor bodies in our Solar System, throughgalaxies in the nearby Universe, to some 500 000 distant quasars. It will provide a number of stringent new testsof general relativity and cosmology. The complete satellite system was evaluated as part of a detailed technologystudy, including a detailed payload design, corresponding accuracy assesments, and results from a prototype datareduction development.