Microarcsecond astrometric observatory Theia: from dark matter to compact objects and nearby earths

Theia is a logical successor to Gaia, as a focused, very high precision astrometry mission which addresses two key science objectives of the ESA Cosmic Vision program: the nature of dark matter and the search for habitable planets. Theia addresses a number of other science cases strongly synergistic with ongoing/planned missions, such as the nature of compact objects, motions of stars in young stellar clusters, follow-up of Gaia objects of interest. The "point and stare" operational mode will enable Theia to answer some of the most profound questions that the results of the Gaias survey will ask. Extremely-high-precision astrometry at 1-pas level can only be reached from space. The Theia spacecraft, which will carry a 0.8-m telescope, is foreseen to operate at L2 for 3,5 years. The preliminary Theia mission assessment allowed to identify a safe and robust mission architecture that demonstrates the mission feasibility within the Soyuz ST launch envelope and a small M-class mission cost cap. We present here the features of the mission that has been submitted to the last ESA M4 call in January 2015.