Gaia and the Hunt for Extra - Solar Planetsm

We present the results of realistic end-to-end simulations of observations of nearby stars with the proposed global astrometry mission GAIA, recently recommended within the context of ESA's Horizon 2000 Plus long-term scientiic program. We show that under realistic, if challenging, assumptions, GAIA will be capable of surveying the solar neighborhood within 100{200 pc for the astrometric signatures of planets around stars down to V = 16 mag. The wealth of results on the frequency and properties of massive planets from GAIA observations will provide a formidable testing ground on which to confront the most sophisticated theories on planetary formation and evolution. Finally, we suggest the possibility of more sophisticated probabilistic detection techniques which may be able to detect the presence of Earth-like planets around stars within 20 pc.