  The detectors designed for Gaia, the next ESA space astrometry mission to be
launched in 2011, will allow to observe repeatedly stars very close to
Jupiter's limb. This will open a unique opportunity to test General Relativity
by performing many Eddington-like experiments through the comparison between
the pattern of a starfield observed with or without Jupiter. We have derived
the main formulas relevant for the monopole and quadrupole light deflection by
an oblate planet and developed a simulator to investigate the processing of the
Gaia astrometric observation in the vicinity of the planet. The results show
that such an experiment carried out with the Gaia data will provide a new fully
independent determination of the PPN parameter gamma by means of differential
astrometric measurements and, more importantly, for the first time will
evidence the bending effect due to the quadrupole moment with a 3-sigma
confidence level. Given the accuracy of the experiment for the monopole
deflection, this will permit to test alternative modelling of the light bending
by moving masses.
