PRIMA, the instrument for Phase Referenced Imaging and Micro-arcsecond Astrometry, will implement the dual-feed capability at the ESO Very Large Telescope Interferometer (VLTI).

ESPRI will use PRIMA to combine the K-band light from two 1.8m diameter Auxiliary Telescopes (ATs) and interferometrically measure with very high accuracy the angular separation between two stars (astrometry). One of the two stars will typically be a distant background star (the reference star), the other one a nearby target star. From the relative motion of the two stars we will deduce the existence and orbital parameters of planets around the target star.

In order to reach this goal, a consortium lead by the Observatoire de Geneve (Switzerland), the Max Planck Institute for Astronomy, and the Landessternwarte Heidelberg, is currently building the Differential Delay Lines for PRIMA and develops the astrometric data reduction software and all necessary astrometric operation tools. The PRIMA facility is planned to become fully operational in 2011.

MPIA is involved with the science program, the development of the Differential Delay Line (DDL) hardware, the error budget, the development of the strategy and planning of observations and the data reduction software.