Wind-driven surface waves on Titan

The surface of Titan represents the largest surface area in the solar syste m essentially unexplored, although recent observations from Hubble Space Te lescope and ground-based telescopes using adaptive optics have given perhap s the first low-resolution indications of its nature. Whilst early models c iting global oceans have been all but abandoned, substantial bodies of liqu id up to several hundred kilometers in extent are not precluded. if such re servoirs 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 rema ins the dominant controlling factor for such waves, with surface tension an d viscous effects only becoming significant below wavelengths of several ce ntimeters, Empirical models used for terre strial wind-driven sea waves are adapted to investigate the properties of such waves on Titan using predict ed parameters for Titan's liquids. Significant wave height, peak period, wa velength, phase speed, and wave steepness are predicted as a function of wi nd speed and liquid body extent. It is found that waves will grow to a limi ting height, limiting wavelength and limiting period which are all inversel y proportional to gravity. The limiting significant wave height under the a ction 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 intere sting, however, is the wave growth prior to this limiting value. A useful v isualization is that surface waves on a Titan sea arising fi om surface win d speeds of 0.3 and 1 m s(-1) will resemble in scale waves on Earth generat ed by terrestrial winds of 1 and 3 m s(-1) respectively. These particular T itan waves will have nearly 3 times the period and travel almost 3 times sl ower than the terrestrial waves, however. The wave parameters predicted in this work have potential surface mission implications for the European Spac e Agency's Huygens Probe which will land on Titan in 2004. Conversely, thei r measurement by instruments on board Huygens and NASA's Cassini spacecraft could yield important planetological information.