Titan, Saturn's largest moon, with a diameter of 5150 km and a surface pressure of 1.5 bar, is revealing itself to Cassini-Huygens as a very complex and dynamic world. On a 16-day time scale (the length of Titan's day and also its period around Saturn), tides rise and fall in seas and lakes of hydrocarbons, winds are driven in the atmosphere, and stresses are created deep in the interior.
From year-to-year, seasonal changes are expected in the atmosphere and on the surface, in the atmospheric composition and temperature, in the aerosol concentration, in the clouds, in the wind patterns and in the lakes and seas. Many analogs to the Earth have been found in the organic-rich, icy environment of Titan.
Cassini-Huygens has revealed Titan's surface eroded by fluvial activity, and in some places precipitation may be torrential enough to cause flash floods. The atmosphere exhibits a greenhouse effect like Earth's. Clouds, dunes, rivers, lakes, seas, possibly ice volcanoes, and stratospheric anomalies analogous to our planet's ozone hole have been observed.
Enceladus, only 500 km in diameter, is also surprising us. To the Cassini instruments, this puzzling little moon revealed dramatic organic-laden jets of water vapour and dust-sized ice particles emanating from its south polar region (marred by narrow tectonic rifts called tiger stripes, probably containing organics), possibly from liquid water reservoirs just below the icy surface.
The main mission goals are to investigate thoroughly the two most intriguing moons of Saturn, Titan and Enceladus and their connection to the overall Saturn system. More specifically, the mission will address the following objectives:
- Conduct a thorough investigation of Titan's space environment: atmosphere, ionosphere and exosphere as well as its plasma and magnetic field environment. Of particular interest is the 800-200 km transition region, a key component in understanding the entire atmosphere and the origin of the organic molecules that it produces.
- Characterise the neutral atmosphere in terms of temperature, pressure, wind fields and CH4 and C2H6 humidity
- Study the internal structure and evolution of clouds; haze characteristics; evaporation rates and temperature over lakes; surface composition and thermal properties
- Map Titan's surface from orbit with resolutions <100 m, and at much higher resolution (< 1 m) from the in-situ elements, including compositional context and infrared imaging
- Explore Titan's and Enceladus' interior structure and bulk composition by quantifying spatial and temporal variations rotation, topography, gravity field, magnetic field, seismicity, and surface properties
- Obtain constraints on Titan and Enceladus formation and evolution models, in particular isotopic ratios to constrain the origin and cycle of methane on Titan, isotopic ratios and the origin of the plumes and jets emanating from Enceladus' southern hemisphere
- Study the potential for astrobiological studies and the potential habitability of these two objects
- Perform Saturn System science, particularly as it pertains to understanding formation and evolution of Titan and Enceladus