  We provide a revised assessment of the number of exoplanets that should be
discovered by Gaia astrometry, extending previous studies to a broader range of
spectral types, distances, and magnitudes. Our assessment is based on a large
representative sample of host stars from the TRILEGAL Galaxy population
synthesis model, recent estimates of the exoplanet frequency distributions as a
function of stellar type, and detailed simulation of the Gaia observations
using the updated instrument performance and scanning law. We use two
approaches to estimate detectable planetary systems: one based on the S/N of
the astrometric signature per field crossing, easily reproducible and allowing
comparisons with previous estimates, and a new and more robust metric based on
orbit fitting to the simulated satellite data.
  With some plausible assumptions on planet occurrences, we find that some
21,000 (+/-6000) high-mass (1-15M_J) long-period planets should be discovered
out to distances of ~500pc for the nominal 5-yr mission (including at least
1000-1500 around M dwarfs out to 100pc), rising to some 70,000 (+/-20,000) for
a 10-yr mission. We indicate some of the expected features of this exoplanet
population, amongst them ~25-50 intermediate-period (P~2-3yr) transiting
systems.
