The Exploration of Titan with an Orbiter and a Lake-Probe

Titan, Saturn's largest satellite, is a unique object in the Solar System presenting a substantial atmosphere, a surface with a complex interplay of geological processes and an outer ice shell overlying a subsurface ocean. The climate on this icy satellite boasts a multi-phase hydrological cycle where methane plays a role similar to water on Earth. The Cassini-Huygens mission to the Saturn system, which is still ongoing, accomplished a first in-depth exploration of Titan showing extended hydrocarbon lakes and seas in Titan's polar regions which, combined with extensive equatorial dune deposits, form the largest reservoir of organics in the solar system. The presence of standing bodies of liquid, dissected fluvial channels, tectonic features, vast dune fields and putative cryovolcanic flows express striking analogies with terrestrial geological activity. Titan is the only other place in the Solar System with the Earth to have lakes and seas. In spite of all its advances, the Cassini-Huygens mission, due to its limited instrumentation and timeline among other, cannot address some fundamental questions such as "What are the complex organic molecules that form the dune material, and how have they been formed?" and "What is the composition of the lakes and seas". Cassini has demonstrated that there must be exchanges between the interior and the atmosphere: "What are the processes that form the atmosphere?" and "Is Titan endogenically active?" We discuss how the future exploration of Titan can benefit from a dedicated orbiter and an in situ lake-probe that would address central themes regarding the nature and evolution of this icy satellite and its organic-rich environment. Prior to an orbiter phase around Titan and an in situ exploration of its lakes, mission scenarios could also involve investigations of the planet Saturn and its other satellites including the geologically active icy moon Enceladus.