The objectives of the optional ExoMars Programme are two-fold:
The scientific objectives are to target the questions of past and present life on Mars, investigating the presence of water and the geochemical environment as well as atmospheric trace gases and their sources.
The technological objectives are the safe landing of a payload on Mars, exploring the surface with a rover, and acquiring subsurface samples and subsequently performing in-situ analysis.
These objectives shall be reached with two different missions scheduled for 2016 and 2018, respectively. The 2016 mission includes a Trace Gas Orbiter (TGO) and an Entry, Descent and Landing Demonstrator Module (EDM). The 2018 mission includes a European Carrier spacecraft to place a European Rover on the surface of Mars. The Rover will carry a drill and a suite of instruments dedicated to exobiology and geochemistry research.
Through an elaborate international cooperation Roscosmos will provide a Proton launcher for both missions.
The extensive website of Robotic Exploration of Mars provides detailed background information of the spacecrafts, their modules, the payload and an up-to-date programme timeline.