Evolution of Titan's Seas and Lakes during Northern Spring
Abstract:Titan is the only body in the solar system, besides Earth, to have stable liquid seas at its surface . The three main seas, known as Kraken Mare, Ligeia Mare, and Punga Mare are located at the North Pole where they cover a surface area of 500,000-, 126,000-, and 50,000-km2, respectively. In addition, several hundreds of small lakes are present, raising the questions of their relationships with the large seas. These hydrocarbon lakes and seas can be better imaged at optical wavelengths as the season moves towards summer solstice. At the same time, the North Pole area is receiving more solar light, which modifies the atmospheric circulation. Global Circulation Models (GCMs) predict stronger winds, more evaporation, and formation of methane clouds .
The Visual and Infrared Mapping Spectrometer (VIMS) has observed the North Pole area during several high inclined flybys. Mosaics in seven infrared atmospheric windows have been constructed. Several units can be distinguished by their surface albedo. The 5-micron bright unit has been interpreted as evaporitic material based on its location relative to the lakes and seas . The spectral characteristics cannot be matched by a simple mixture of water ice and ‘typical Titan organic material’ known as tholins. The composition of these different units is therefore still enigmatic. In addition, some of the spectral characteristics may be related to the texture of the units.
The few passes over the North Pole have allowed the VIMS team to image some places several times looking for changes on the surface or/and in the lower atmosphere. Although GCMs predict evaporation of the seas and lakes and the formation of methane clouds , neither changes in the shorelines, nor clouds have been identified. Very recent specular reflection observations suggest the formation of waves on Punga , and therefore more active winds. In addition, the VIMS recently observed a brightening of the area between Punga, Kraken and Ligeia. Whether this change is related to surface processes or evaporation of the seas is being investigated.
This work has been performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA.
 Stofan E.R. et al., Science, 2007 ;  Schneider T. et al., Nature, 2012 ;  MacKenzie S.M. et al., Icarus, in press ;  Barnes J.W., Ap.J., 2014.