Reference frame linking and tests of GR with Gaia astrometry of asteroids

The Gaia satellite, an ESA cornerstone mission to be launched at the end of the year 2011, will observe a large number of celestial bodies including also small bodies of the solar system. Albeit spread from the inner to the outer regions of the solar system, these are mainly near-Earth objects and main-belt asteroids. All objects brighter than magnitude V 20 that cross the field of view (i.e. with solar elongation 45◦ L 135◦) of the survey-mode scanning telescope will be observed. The mission will provide, over its 5 years duration, high precision photometry and astrometry with an unprecedented accuracy ranging roughly from 0.3 to 3 milli-arcsecond on the CCD level, and depending on the target’s magnitude. In addition, several hundreds of QSOs directly observed by Gaia will provide the kinematically non-rotating reference frame in the visible light, resulting in the construction of a ’Gaia-ICRF’. The positions of the asteroids hence enable to relate the dynamical reference frame—as defined by the equations of motion—to the kinematic one, and to further check the non-rotating consistency between both frames’ definition. Here we show the results of a variance analysis obtained from a realistic simulation of observations for such a link. The simulation takes into account the time sequences and geometry of the observations that are particular to Gaia observations of solar system objects, as well as the instrument sensitivity and photon noise. Additionally, we show the achievable precision for the determination of a possible time variation of the gravitational constant Ġ/G. Taking into account the non-completeness of the actually known population of NEOs, we also give updated values for the nominal precision of the joint determination of the solar quadrupole J2 and PPN parameter β.