ESPRESSO: the ultimate rocky exoplanets hunter for the VLT

ESPRESSO, the VLT rocky exoplanetshunter, will combine the efficiency of modern echelle spectrographwith extreme radial-velocityprecision. It will be installed at Paranal on ESO's VLT in order to achieve a gain of two magnitudes with respect to its predecessor HARPS, and the instrumental radial-velocityprecision will be improved to reach 10 cm/s level. We have constituted a Consortium of astronomical research institutes to fund, design and build ESPRESSOon behalf of and in collaboration with ESO, the European Southern Observatory. The project has passed the preliminary design review in November 2011. The spectrographwill be installed at the so-called "Combined Coude Laboratory" of the VLT, it will be linked to the four 8.2 meters Unit Telescopes (UT) through four optical "Coude trains" and will be operated either with a single telescope or with up to four UTs. In exchange of the major financial and human effort the building Consortium will be awarded with guaranteed observing time (GTO), which will be invested in a common scientific program. Thanks to its characteristics and the ability of combining incoherently the light of 4 large telescopes, ESPRESSOwill offer new possibilities in many fields of astronomy. Our main scientific objectives are, however, the search and characterization of rocky exoplanetsin the habitable zone of quiet, near-by G to M-dwarfs, and the analysis of the variability of fundamental physical constants. In this paper, we present the ambitious scientific objectives, the capabilities of ESPRESSO, the technical solutions for the system and its subsystems, enlightening the main differences between ESPRESSOand its predecessors. The project aspects of this facility are also described, from the consortium and partnership structure to the planning phases and milestones.