Microarcsecond light bending by Jupiter

The detectors designed for Gaia, the next ESA space astrometry mission to be launched in 2011, will allow us to repeatedly observe 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 formulae relevant for the monopole and quadrupole light deflection by an oblate planet and have developed a simulator to investigate the processing of the Gaia astrometric observations 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 γ 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 3σ confidence level. Given the accuracy of the experiment for the monopole deflection, this will permit testing of alternative models of light bending by moving masses.