Sea Technology

JUN 2014

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Page 33 of 76 June 2014 / st 33 waves. Given maximum GCM wind- speed predictions of about 2 meters per second in summer, the signifcant wave height is expected to reach about 80 centimeters. Therefore, shoreline ero- sion and beach processes are possible on Titan. Given the low-density con- trast between ice bedrock and hydro- carbon liquid along with low gravity, sediments should be readily mobilized in Titan's seas. Since the relative humidity of meth- ane on Titan is only about 50 percent, a body of pure methane cannot persist indefnitely on Titan's surface since it is not in thermodynamic equilibrium. The evaporation rate has been estimated at up to 1 meter per year, using ter- restrial empirical transfer coeffcients, although this is strongly dependent on wind speed. The evaporation rate is composition-dependent, in that the sat- uration vapor pressure of ethane is very low, so ethane acts to suppress the par- tial pressure of methane above mixed- composition seas (much as syrup will evaporate in a kitchen much more slowly than water). Titan's air-sea in- teractions have some complexities not usually faced on Earth. While ethane probably migrates only over long peri- ods (more than 10,000 years), evapora- tion and precipitation of methane may be much more like terrestrial weather, with hourly and seasonal changes as well as longer-term effects. In fact, transient surface darkening has been observed at low latitudes on Titan in association with methane clouds. Fol- lowed by brightening, this suggests that shallow fooding occurred, followed by evaporation—the hydrological cycle is clearly active today. Conclusion Titan's landscape, atmosphere and climate system have many parallels with Earth, with the added interest of the astrobiological implications of Ti- tan's prebiotic chemistry and rich in- ventory of organics. Thus Titan is an important target for future exploration. The Cassini mission, in the Saturn sys- tem since 2004, continues to operate well and makes several Titan encoun- ters per year. A wide range of concepts has been advanced for future explora- tion of Titan, including hot air balloons, airplanes, orbiters, helicopters and even hovercraft, exploiting Titan's low gravity and thick, cold atmosphere. Recently, Titan's seas were the fo- cus of a mission evaluated by NASA, the Titan Mare Explorer (TiME), which would feature a capsule delivered by parachute to Ligeia. This vehicle would be launched in 2016 to arrive in 2023, permitting the Earth to be visible from Ligeia's high northern latitude and al- lowing a direct-to-Earth data transmis- sion, without requiring an expensive orbital relay. The capsule would oper- ate over three months (six Titan days) measuring the liquid composition and turbidity, studying sea-surface condi- tions and air-sea exchange processes with cameras and meteorological in- struments, and exploring the seabed with a depth sounder. In that time, it is expected to drift several kilometers per day, perhaps reaching the shoreline. Further exciting proposals to study Titan and its seas can be expected. In the meantime, ongoing Cassini obser- vations (planned to operate until north- ern midsummer in 2017) will doubtless reveal new surprises about Titan's alien seas. n Dr. Ralph Lorenz is a planetary scientist at the Johns Hopkins University Applied Physics Laboratory. More information on his work can be found by visit- ing the website Hydrographic Equipment & Software Teledyne TSS Motion & Navigation Systems And the following are on GSA! Chesapeake Technology SonarWiz Teledyne ODOM Echo Sounders & Multibeam Systems Hydrographic Equipment & Software And the following are on GSA! Hemisphere GPS Bluefin Robotics AUVs TELEDYNE TSS EdgeTech Marine Side Scan Sonars, Subbottom Profilers & Integrated Systems JUN2014.indd 33 6/4/14 1:04 PM

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