Wind-driven surface waves on Titan

The surface of Titan represents the largest surface area in the solar system essentially unexplored, although recent observations from Hubble Space Telescope and ground-based telescopes using adaptive optics have given perhaps the first low-resolution indications of its nature. Whilst early models citing global oceans have been all but abandoned, substantial bodies of liquid up to several hundred kilometers in extent are not precluded. if such reservoirs do exist then in the presence of any surface winds it is expected that wind-driven surface waves will be generated. As on Earth, gravity remains the dominant controlling factor for such waves, with surface tension and viscous effects only becoming significant below wavelengths of several centimeters, Empirical models used for terre strial wind-driven sea waves are adapted to investigate the properties of such waves on Titan using predicted parameters for Titan's liquids. Significant wave height, peak period, wavelength, phase speed, and wave steepness are predicted as a function of wind speed and liquid body extent. It is found that waves will grow to a limiting height, limiting wavelength and limiting period which are all inversely proportional to gravity. The limiting significant wave height under the action of a 1 m s(-1) Titan wind over 50 km, for example, is predicted to be 0.2 m compared to 0.02 m On Earth under similar circumstances, More interesting, however, is the wave growth prior to this limiting value. A useful visualization is that surface waves on a Titan sea arising fi om surface wind speeds of 0.3 and 1 m s(-1) will resemble in scale waves on Earth generated by terrestrial winds of 1 and 3 m s(-1) respectively. These particular Titan waves will have nearly 3 times the period and travel almost 3 times slower than the terrestrial waves, however. The wave parameters predicted in this work have potential surface mission implications for the European Space Agency's Huygens Probe which will land on Titan in 2004. Conversely, their measurement by instruments on board Huygens and NASA's Cassini spacecraft could yield important planetological information.