Monday, 25 September 2017

Saturn’s moon Titan and Its Seas of Tranquility

Saturn’s moon Titan and Its Seas of Tranquility

Imagine sailing on the calm seas of another world, without a care in the world, or at least not a care in that other world. If you were sailing on one of the seas (or lakes) on Saturn’s large moon Titan, you wouldn’t have to worry about your boat being swamped by giant waves.  At least, that’s what some recent evidence suggests.

Of course you would still have a few other worries, like incredibly cold temperatures and lack of an oxygen atmosphere, but at least capsizing your boat wouldn’t be much of an issue. It would be a true Sea of Tranquility, much more aptly named that the landing site for Apollo 11, on the Earth’s moon.  According to these new findings, the height of the waves (amplitude) shouldn’t exceed a centimeter or so, and the distance between the waves (wavelength) shouldn’t be more than 5 to 10 centimeters.

And the view would be pretty amazing, until you got tired of a permanently hazy brown sky, rather like a smoggy day over a big polluted city.  

A recent paper (June 2017) in the journal “Earth and Planetary Science Letters” has used data from the Cassini orbiter, to estimated the conditions on the hydrocarbon lakes on Saturn’s moon Titan.  The researchers, based at several U.S. universities, used data from the Cassini RADAR altimetry mode to estimate the amplitude and wavelength of waves on several large liquid hydrocarbon bodies.  Those bodies are in the northern hemisphere of Titan, Ligeia Mare, Kraken Mare and Punga Mare (“mare” means “sea” in Latin).

Essentially, the researchers took radar data from Cassini, and ran it through what is called a classic specular mode.  The emitted signal is known, and the returned signal, after bouncing off of the liquid surfaces is analysed for changes that would be expected from signals being reflected off of such a surface.  Some fairly complicated theoretical mathematical modelling and statistical analysis is used, to determine the actual surface characteristics of the liquid (amplitude, wavelength, substance).  The theoretical models have some free parameters that can be varied, until a good fit with the actual data is achieved.  From that, the amplitude and wavelength of the waves on the surface can be inferred.  At least, that’s my interpretation – the interested reader can inspect the original paper for greater details.

There has been some long range planning about dropping another probe onto the surface of Titan, which would be much longer lasting than the Huygens probe (which produced the photo below). Huygens only had a short time to produce this photo, along with some other analysis.

One proposal is to have a floating lander, that could sail on one of the hydrocarbon lakes, to study it in greater detail.  It would be a nice touch if the probe studied the Kraken Mare, and was therefore given the same name.  Then, some future mission scientist could say these immortal words, while first sending the probe across the hydrocarbon sea:

“Release the Kraken”.


Earth and Planetary Science Letters

Surface roughness of Titan’s hydrocarbon seas
CyrilGrimaa,, MarcoMastrogiuseppeb, Alexander G.Hayesb, Stephen D.Wallc, Ralph D.Lorenzd, Jason D.Hofgartnerc, BryanStilesc, CharlesElachic, TheCassiniRADARTeam

Here are a few facts about Titan, courtesy of Wiki:

  • It's the second biggest moon in the solar system (about 2575 km radius, slightly smaller than the Jovian moon Ganymede).  It is about 50% larger than our moon.
  • It was discovered in 1655 by Huygens, the first moon of Saturn discovered and the fifth moon in all (excepting our own).
  • It is primarily made of ice and rock, apparently about half and half, based on its overall density.  It also has a dense atmosphere, which made telescope observations of the surface difficult.
  • The Cassini-Huygens space probe recently visited the system (2004) and established the fact that Titan has a methane cycle, similar to Earth’s water cycle.  Naturally, the methane cycle is at a much lower temperature than the Earth’s water cycle.
  • The Huygens probe actually sent back images from the surface, which is awesome when you think about it.
  • Titan is orbitally locked with Saturn, much like our moon is with Earth.  Thus, it always shows one side to the planet.
  • There appears to be a subsurface ocean, based on some Cassini observations. It may be water and ammonia, thus liquid at lower temperatures than on Earth.  The heat would be from the deep interior of the moon, rather than tidal heating as is the case with Jovian moons.
  • The atmosphere is mostly nitrogen (98.4%), and somewhat denser than Earth’s atmosphere (1.45 atmospheres pressure).  The remainder is methane and some trace hydrocarbons.  This produces smog of the characteristic orange colour.  The methane appears to be continuously generated from the interior.
  • It’s a bit on the cool side on the surface, about -180 Celsius, compared to Earth’s balmy average of about +20 degrees.
  • The surface appears to be fairly young.  The methane cycle sculpts it, the way the water cycle does on Earth, with lakes, river channels and the like.  There may also be volcanism, though spewing water rather than magma.
  • There appears to be some mountain ranges, though not nearly as long or as high as on the Earth.  There are few craters, a result of a thick protective atmosphere and a geologically active surface.
  • There are highly speculative theories that life could exist on Titan, with methane or ethane acting as a solvent, in place of water for Earth life.  Such organisms might breathe hydrogen rather than oxygen, and metabolize acetylene rather than glucose, exhaling methane rather than CO2.

Here's a picture of Titan, taken by the Cassini probe in 2005.

Perhaps you would like to read about a nice hike along a not so tranquil shore, on our own green and blue planet.  If so, you might consider “A Walk on the Juan de Fuca Marine Trail”, a beautiful hike on the western shore of British Columbia, Canada.

The Juan De Fuca Marine is considered by many to be one of Canada’s finest hiking trails. It hugs the south-western shore of Vancouver Island, between Jordan River and Port Renfrew for a distance of about 48 kilometres. Like its (perhaps) more famous neighbouring hiking trail just to the north, The West Coast Trail, it features both beach and forest hiking along a rugged coastline. The hiking is a nice test of one’s fitness, the views are spectacular, the wildlife (marine and forest) is plentiful and the people are friendly. What more could one ask for? 

What follows is a journal of a five day trip, taken in early September of 2002. It is about 13,000 words in length (60 to 90 minutes reading), and contains numerous photographs of the trail. There are also sections containing a brief history of the trail, geology, flora and fauna, and associated information.