Mystery of the Missing Waves on Titan   
       
   July 22, 2013:  One of the most shocking discoveries of the past 10 years is   
   how much the landscape of Saturn's moon Titan resembles Earth.  Like our own   
   blue planet, the surface of Titan is dotted with lakes and seas; it has river   
   channels, islands, mud, rain clouds and maybe even rainbows.  The giant moon   
   is undeniably wet.   
       
   The "water" on Titan is not, however, H2O.  With a surface temperature dipping   
   290 degrees F below zero, Titan is far too cold for liquid water. Instead,   
   researchers believe the fluid that sculpts Titan is an unknown mixture of   
   methane, ethane, and other hard-to-freeze hydrocarbons.   
       
   http://www.youtube.com/watch?v=-pj4G101o-M   
       
   A new ScienceCast video ponders the mystery of the missing waves on Titan.   
   Play it   
       
   The idea that Titan is a wet world with its own alien waters is widely   
   accepted by planetary scientists. Nothing else can account for the   
   observations: NASA's Cassini spacecraft has flown by Titan more than 90 times   
   since 2004, pinging the Moon with radar and mapping its lakes and seas. ESA's   
   Huygens probe parachuted to the surface of Titan in 2005, descending through   
   humid clouds and actually landing in moist soil.   
       
   Yet something has been bothering Alex Hayes, a planetary scientist on the   
   Cassini radar team at Cornell University.   
       
   If Titan is really so wet, he wonders, "Where are all the waves?"   
       
   Here on Earth, bodies of water are rarely still.  Breezes blowing across the   
   surface cause waves to ripple and break; raindrops striking sea surfaces also   
   provide some roughness.  Yet on Titan, the lakes are eerily smooth, with no   
   discernable wave action down to the millimeter scale, according to radar data   
   from Cassini.   
       
   "We know there is wind on Titan," says Hayes. "The moon's magnificent sand   
   dunes [prove] it."   
       
   Add to that the low gravity of Titan-only 1/7th that of Earth-which offers so   
   little resistance to wave motion, and you have a real puzzle.   
       
   http://www.nasa.gov/mission_pages/cassini/whycassini/cassini20091217.html   
       
   This glint of sunlight detected by Cassini in 2009 is widely thought to be a   
   reflection from the mirror-like surface of one of Titan's northern lakes.   
   MoreResearchers have toyed with several explanations.  Perhaps the lakes are   
   frozen. Hayes thinks that is unlikely, however, "because we see evidence of   
   rainfall and surface temperatures well above the melting point of methane." Or   
   maybe the lakes are covered with a tar-like substance that damps wave motion.   
   "We can't yet rule that out," he adds.   
       
   The answer might be found in the results of a study Hayes and colleagues   
   published in the July 2013 online edition of the journal Icarus. Taking into   
   account the gravity of Titan, the low viscosity of liquid hydrocarbons, the   
   density of Titan's atmosphere, and other factors, they calculated how fast   
   wind on Titan would have to blow to stir up waves: A walking-pace breeze of   
   only 1 to 2 mph should do the trick.   
       
   This suggests a third possibility: the winds just haven't been blowing hard   
   enough. Since Cassini reached Saturn in 2004, Titan's northern hemisphere   
   (where most of the lakes are located) has been locked in the grip of winter.    
   Cold heavy air barely stirs, and seldom reaches the threshold for wave-making.   
       
   But now the seasons are changing. In August 2009 the sun crossed Titan's   
   equator heading north. Summer is coming, bringing light, heat and wind to   
   Titan's lake country.   
       
   "According to [climate models], winds will pick up as we approach the solstice   
   in 2017 and should be strong enough for waves," he says.   
       
   If waves appear, Cassini should be able to detect them.  Radar reflections   
   from wavy lake surfaces can tell researchers a great deal.  Wave dimensions,   
   for instance, may reveal the viscosity of the underlying fluid and, thus, its   
   chemical composition.  Also, wave speeds would track the speed of the   
   overlying winds, providing an independent check of Titan climate models.   
       
   Hayes is excited about "bringing oceanography to another world. All we need   
   now," he says, "are some rough seas."   
       
   Credits:   
       
   Author:Dr. Tony Phillips| Production editor: Dr. Tony Phillips | Credit:   
   Science@NASA   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.94   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)