  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 scientific
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.
