  We outline a flagship-class mission concept focused on studying Titan as a
global system, with particular emphasis on the polar regions. Investigating
Titan from the unique standpoint of a polar orbit would enable comprehensive
global maps to uncover the physics and chemistry of the atmosphere, and the
topography and geophysical environment of the surface and subsurface. The
mission includes two key elements: (1) an orbiter spacecraft, which also acts
as a data relay, and (2) one or more small probes to directly investigate
Titan's seas and make the first direct measurements of their liquid composition
and physical environment. The orbiter would carry a sophisticated remote
sensing payload, including a novel topographic lidar, a long-wavelength
surface-penetrating radar, a sub-millimeter sounder for winds and for
mesospheric/thermospheric composition, and a camera and near-infrared
spectrometer. An instrument suite to analyze particles and fields would include
a mass spectrometer to focus on the interactions between Titan's escaping upper
atmosphere and the solar wind and Saturnian magnetosphere. The orbiter would
enter a stable polar orbit around 1500 to 1800 km, from which vantage point it
would make global maps of the atmosphere and surface. One or more probes,
released from the orbiter, would investigate Titan's seas in situ, including
possible differences in composition between higher and lower latitude seas, as
well as the atmosphere during the parachute descent. The number of probes, as
well as the instrument complement on the orbiter and probe, remain to be
finalized during a mission study that we recommend to NASA as part of the NRC
Decadal Survey for Planetary Science now underway, with the goal of an overall
mission cost in the "small flagship" category of ~$2 bn. International
partnerships, similar to Cassini-Huygens, may also be included for
consideration.
