Astrometry as an Exoplanet Discovery Method

Astrometry consists in measuring the positions and the motions of the astronomical objects on the sky compared to other stars. The increased accuracy of such measurements opens the way to determine not only the proper motions of stars and their parallactic displacements due to Earth motion around the Sun but also the orbital motion caused by the presence of orbiting planets of all nature. Several techniques have been investigated using different types of instrument with limited impact on exoplanet detection so far, but the technique has not only great potentials but is complementary to other discovery methods. The importance of stability and precision of the astrometric measurements over a long period may explain the relative lack of results, but the advent of a space mission like Gaia will certainly change the impact of astrometry in the exoplanet field.