A Glassy Sea on Titan

by Paul Gilster on March 24, 2014

The second largest sea on Titan is Ligeia Mare, made up of methane and ethane in a body of liquid that is larger than Lake Superior. Now we have word that the surface of Ligeia Mare is so utterly still that it would appear like glass. The news comes from Stanford University, where geophysicist Howard Zebker had led a new study based on Cassini measurements made in 2013. “If you could look out on this sea,” said Zebker, “it would be really still. It would just be a totally glassy surface.”

Titan seizes the imagination not only because it is planet-like, with seas and a thick atmosphere, but because we know of no other body in the Solar System besides Earth that has a complex cycle involving solid, liquid and gas. Because the thickness of Titan’s atmosphere compromises optical observations, Cassini bounced radio waves off the surface and analyzed the resulting echo. Wave action could be measured by the strength of the returning echo. Zebker explains in this Stanford news release that the echo is analogous to an Earthly lake which, if completely still, would reflect an extremely bright image of the Sun, while a surface in motion would produce a much dimmer reflection.



Given that Cassini’s radar sensitivity is one millimeter in this study, any waves on Ligeia Mare would have to be smaller than one millimeter, which makes for a smooth surface indeed. Cassini’s only comparable observation occurred in a late 2008 Titan flyby that studied Ontario Lacus, with both studies indicating an equally smooth surface. Lack of winds during the time of observation is one explanation for the calm seas, but a layer of material could also suppress any waves. Says Zebker: “[O]n Earth, if you put oil on top of a sea, you suppress a lot of small waves.”

Also interesting here is that radiometry measurements of the terrain surrounding Ligeia Mare show little surface water ice. Instead, the area seems to be made up of solid organic materials, probably the same methane and ethane constituents that make up the sea itself.

Talking about Titan’s seas reminds me inevitably of Michael Swanwick’s Hugo winning novelette “Slow Life,” which ran in Analog in 2002. In it, astronaut Lizzie O’Brien finds herself landing at the shore of one such sea. This snippet gives you the flavor of the story:



What happens next involves unusual dreams, robotic exploratory ‘fish’ and a plunge into liquid ethane. You can track this one down in Swanwick’s short story collection The Dog Said Bow-Wow (Tachyon, 2007). We’re going to get a lot of interesting science fiction as the exploration of Titan continues. Meanwhile, the Zebker paper is “Surface of Ligeia Mare, Titan, from Cassini altimeter and radiometer analysis,” published online by Geophysical Research Letters 30 January 2014 (abstract).


ljk March 24, 2014 at 12:04

To use the phrase about people often not seeing the forest for the trees and influenced/inspired by the quote from the science fiction story in the main article, what if Titan itself (or at least its surface) IS the living being, rather than say some exotic fish swimming in one of its lakes (which are awfully darn still if they are supposed to be full of creatures larger than microbes or algae).

If we want there to be life on a place like Titan then we have to “play” by its rules. This means that we have to go with what would really work on that moon and get past our one data point for life Earth. I know it is hard, but so long as we keep thinking the galaxy is set up like it is in Star Trek, we will continue to miss the other possibilities. A few folks are making traction in this regard but there is still a long way to go.

Why aren’t ETI signaling or visiting us? Because if they are anything like the concepts of Titan or Solaris, they move and think too slow for us to grasp their true natures. Plus they seem to have no plans to move out any time soon.

SETI and exoplanetary astronomers keep searching for that Holy Grail they think is another place like our planet. Instead I have to wonder if Titans and Europas are the more likely prospects for life in the galaxy in terms of sheer numbers?

ljk March 24, 2014 at 12:43

Even better news for moons having life as aren’t most star systems in the galaxy doubles or more:


Though I doubt there are very many of them with some young punk staring into the double sunsets and wishing he were out there battling repressive galactic empires. But ya never know.

ljk March 24, 2014 at 14:19

I just have to say this out loud: We now have the ability to detect waves only a few centimeters high on a lake made of liquid ethane on a moon circling a giant planet over 800 million miles from Earth.

This is the kind of stuff our society should be focusing upon.

Alex Tolley March 24, 2014 at 14:19

There was a previous report about waves on another body of liquid on Titan, although they couldn’t rule out a solid, flat surface. It seems to me that the observations of a very flat surface could easily be tested on Earth, both by simulation and experiment. This might confirm that the seas/lakes will/will not create waves under Titan conditions under various surface wind velocities.

Alex Tolley March 24, 2014 at 14:33

@lkj – also like the “Amoebic Sea” in Barlowe’s “Alien Planet”.

The problem for life on Titan are the consequences of very slow chemical reactions. They could be sped up by catalysis, but the very slow chemistry means it might take an extremely long time to evolve those catalysts.

If life was just one giant “cell”, it would still be subject to the slow chemistry, and it certainly isn’t clear to me what advantage large size has for metabolic success.

Perhaps we need to think of pseudo life instead, perhaps one using physical processes rather than chemical to extract and convert something from the environment. One could imagine perhaps some sort of computational being whose form allows “reacting” to changes in the environment without any intermediate chemistry/biochemistry.

Gerry March 24, 2014 at 23:43

I wonder what it would be like to wade through one of Titan’s shallow lakes of liquid hydrocarbons? Would it be a viscid soup or thinner than water on Earth? Would there be a oily skin on the surface, and clearer fluid beneath, like the La Brea Tar Pits?

Would liquid ethane or methane be translucent, if you were to go SCUBA diving? I suppose one would need a pretty well insulated suit, to avoid having all one’s body heat quickly sucked away (a problem in the thick, dense atmosphere as well…)

I seem to remember reading that it’s much more difficult to float on liquid hydrocarbons than on water, so a floating probe would need to displace a greater area than would a boat on an Earthly sea. It might look more like a raft, or just be very light weight and hollow. The low gravity on Titan might help there, I suppose.

NS March 25, 2014 at 1:51

Actually even Star Trek had a number of non-humanoid aliens.

The idea behind SETI is not that there are a lot of humanoids on other worlds (highly unlikely) but that “intelligence” and “technology” are generic enough that many creatures may have them even if they are utterly different from us in other ways (to me, this is also highly unlikely, but we won’t know unless we look).

Maybe like ljk says most life is like Solaris, and we’re the outliers. Or maybe there are so many possibilities for life that each world only samples a tiny fraction of them, and no world is typical. Again we won’t know unless we look (and look, and look)…

Hopefully it won’t be too long before we really look at Titan.

norman wells March 25, 2014 at 5:52

The problem is simply that much of our Society largely wonders what can possibly be of interest in detecting waves of 1mm on an ethane lake millions of miles distant from Earth! They do not see it as the astonishing achievement for mankind that it appears to us.

Michael Spencer MLA ASLA March 25, 2014 at 7:30

Thank you, @lkj, for pointing out remarkable technical achievement.

And there’s a novel (by Robert Forward?) about life in the far reaches of the solar system, replete with details on chemistry at extremely low temperatures.

kzb March 25, 2014 at 8:26

Do we know what the local weather was like when the measurements were done?

Or does this leave us with some kind of cryo-tar pit?

Mark March 25, 2014 at 9:02

One way to test the theory of the glassy sea vs large solid flat area… can we have Cassini swing by on its next orbit and drop a loose nut or bolt? Surely on a spacecraft of this complexity there must be a nut or bolt to spare. After impact we simply count the ripples.

We need to stop thinking of Titan as a place for life (even incredibly slow or cold life) and see it for what it really is: The end to all this incessant babbling about running out of fossil fuels that’s been going on since about 1973.

We simply dispatch a couple dozen automated plutonium-powered refineries along with a handful of electromagnetic rail launchers to the surface of Titan and export gasoline and natural gas by the metric boatload back to the home world. Sure the initial cost of getting the equipment there would be high, but once in place we’ll have all the gasoline and natural gas we could ever need dropped to Earth by daily parachute. We can finally realize the utopian society of the future, powered by plentiful gasoline and heated by natural gas that’s too cheap to meter. No more fracking, no more drilling, no more spoiling the earth to extract the black gold. It would mean the end of a long history of middle-eastern wars for oil and the beginnings of 1000 years of peace and prosperity.

Sure, I know what you’re thinking, “but gasoline’s evil, what about the greenhouse gases? What about global warming?” Listen, a technological civilization with the ability to refine and ship Titanian gasoline across a billion miles of outer space is capable of collecting and exporting its greenhouse gasses to a place where they’ll hardly be noticed: Venus.

Alex Tolley March 25, 2014 at 9:46

@kzb some kind of cryo-tar pit This would seem to conflict with the data suggesting the lakes are composed of ethane/methane. Heavier organics like tholins should sink, rather than float. We also have evidence of fluvial processes, indicating that liquids flow[ed] into the lakes. So we have very calm, liquid ethane lakes. The conflicting evidence against calmness is higher altitude wind speeds are high, and we also observe dune fields, which imply surface winds do exist, even if sporadically.

I can only reconcile these observations by assuming that surface wind speeds must usually be low during our observational window, so that the lakes remain calm. This seems hard to believe, especially given the density of the atmosphere, but how else can one explain all the observations unless there is an interpretation error of lake liquid composition?

Alex Tolley March 25, 2014 at 16:05

@Mark – I find it hard to believe that mining hydrocarbons on Titan will prove economic compared to mining coal and converting it to gas and liquid hydrocarbon. If you can send CO2 to Venus, you can certainly send it on any escape velocity. Again, it has to be cheaper to sequester it at the power plant.

Clarke may well be correct that hydrocarbons will make Titan an economic powerhouse in the solar system when we have an off-planet civilization (“Imperial Earth”) but I cannot see the value of those resources to a predominantly Earthbound civilization.

ljk March 25, 2014 at 19:27


By Leonidas Papadopoulos

The voice of the sea is seductive;
never-ceasing, whispering, clamoring, murmuring,

— Kate Chopin, “The Awakening” (1899)

Replete with metaphor and symbolism, Kate Chopin’s seminal novel presented the sea as a source of empowerment and awakening. Taking a cue from the distinguished American author’s fictional work, NASA’s Cassini spacecraft has possibly observed the evidence of waves on the seas of Titan for the first time, prior to the coming of summer on the moon’s northern hemisphere.

Sharing the title of the most intriguing moon in the whole Solar System with Jupiter’s Europa and Saturn’s Enceladus, Titan, according to planetary scientists and astrobiologists, could be considered an analogue of early Earth before the appearance of life. Enveloped in a thick, opaque nitrogen atmosphere, it is the only known world so far, besides Earth, with seas and lakes on its surface.

Although Titan shares a similar geomorphology with Earth, the moon’s chemical composition is vastly different. Its landscapes are covered with hydrocarbons that rain down from the sky, the surface rocks are made of water ice, and the seas and lakes are composed of a mixture of liquid methane and ethane, the elements that make up natural gas on Earth.

Full article here:


To quote:

A proposed mission that was best suited to settle the question of the existence of waves once and for all was the Titan Mare Explorer, or TiME, a low-cost Discovery-class mission proposal to land on the seas of Titan, which was under consideration from NASA during 2012, but eventually wasn’t picked up by the space agency because of budgetary constrains, in favor of the InSight Mars lander mission, scheduled for launch in 2016. The only option now left to explore Titan and the rest of the Saturnian system for the foreseeable future is the intrepid Cassini spacecraft, whose (already extended twice) mission is projected to end in 2017 with a plunge on Saturn’s cloud tops.

kzb March 26, 2014 at 8:58

Alex, yes it’s a puzzle isn’t it? It seems to me, unless we have some indications of the local weather conditions at the time the measurements were done, we can’t conclude anything ?

Liquid ethane is less viscous than water, gravity on Titan is weaker and the atmosphere is denser. All these things should make the liquid surface more sensitive to winds and other disturbances than water bodies on Earth.

But we are told the surface is smooth down to 1mm resolution. So we must have either exceptionally calm weather or there is something adding to the liquid viscosity (or a combination of both). You need long chain polymer molecules to impart viscosity to a solution (I hesitate to say this given the above comments, but, as an example, DNA in solution is extremely viscous). Maybe just long-chain hydrocarbons fit the bill.

Alex Tolley March 26, 2014 at 14:30

@kzb – As I understand it, the problem of long chain polymers increasing the viscosity of the ethane/methane lakes is that the density variation is so great, that the polymers will sink, leaving the surface relatively free of the polymer. For example, the density of liquid ethane is ~ 0.5 g/cm^3, while low density polyethylene is ~ 9 g/cm^3. The low temperatures will mitigate against Brownian motion keeping the polymers well mixed.

This experiment suggested that tholins would not stay mixed. Countering that assessment, this reported experiment suggests that tholins (some at least) could remain dissolved in the ethane.

this paper suggests an intriguing possibility of life tholins can form coacervates.

That [canceled] Titan Mare Explorer mission is looking really attractive to resolve these issues.

Michael March 26, 2014 at 15:16

@kzb March 26, 2014 at 8:58

‘Liquid ethane is less viscous than water…’

At around 90K liquid ethane has a similar viscosity to water at 20 degrees Celsius and methane 1/10 of it. I am not sure if the radar ‘signal’ is picking up the flat ethane surface and ignoring the methane rich topping.

kzb March 27, 2014 at 9:14

I stand corrected on the ethane viscosity. Yes, another option is said to be methane ice, kept afloat by entrained nitrogen bubbles.

it’s also interesting that they are saying this particular lake is almost pure methane, because they can see the bottom. That must constrain the composition of dissolved materials quite a lot.

It’s a pity the Explorer got cancelled of course. But reading those experiments that Alex linked to, you realise that probably the majority of unversities on the planet have the resources to conduct them. They should be relatively inexpensive experiments too.

Michael March 28, 2014 at 14:07

@kzb March 27, 2014 at 9:14

‘Yes, another option is said to be methane ice, kept afloat by entrained nitrogen bubbles.’

This is unlikely as it would present a rough surface (backscatter).


My money would be on propane been the smooth reflective material, at the temperatures on titan it has a viscosity of around ten times that of water at 20 degrees. If the radar penetrates the upper lower density materials such as methane and ethane each would having a calming effect on the wave height at their respective interfaces before the much more viscous propane reflects the radar, it would present a very smooth surface.

Rob Henry March 31, 2014 at 17:10

It seems that everyone else is afraid to invoke the speculative SF answer, so here goes. What if the entire lake is covered in a (single) layer of photosynthetic cells – supported by surface tension and gasbladders as needed.

ljk April 1, 2014 at 9:15

I wasn’t afraid. In fact my first post was asking people to ponder the possibility that Titan’s surface is alive as one immense living being. Of course shots were taken at it, but I say get a lander mission there first, then you better answer my speculation.

Michael April 1, 2014 at 12:20

@Rob Henry March 31, 2014 at 17:10


@ljk April 1, 2014 at 9:15


Although I am a SF fan I will apply Occam’s razor here, it is way too cold on Titan for life. That ‘living film’ as you both have discussed is reflecting light not absorbing it.

ljk April 1, 2014 at 14:59

Michael said on April 1, 2014 at 12:20:


Perhaps it lives off geothermal (or titanthermal) energy from beneath?

Rob Henry April 1, 2014 at 16:07

There is evidence that something is absorbing hydrogen at the surface at a life-like catalytic rate that belies the temperature, so it is hard to rule life out. On Earth, bacteria tend to grow in single layers. These are often shiny not dark, since a layer is thinner than the wavelength of light, and thus a very inefficient absorber.

Michael April 2, 2014 at 12:43

The hydrogen is possibly disappearing due to ethylene formed in the upper atmosphere been converted to ethane with electrostatic discharge ‘lightening’. Lightening has not been found yet on the moon but the conditions that would give rise to it are there.

Rob Henry April 2, 2014 at 17:00

Yes Michael, ultra violet is blocked so effectively in Titan’s atmosphere, that such reactions only occur high in the atmosphere. From memory, that particular one occurs down to only 600km. What puzzles me is why this hypothetical lightening only occurs at ground level, and why is it not a net generator of hydrogen. It belies belief that that sort of chaotic reaction can take hydrogen levels so close to zero exactly at ground level (as far as it can be measured) .

Michael April 3, 2014 at 9:58

@Rob Henry April 2, 2014 at 17:00

‘…What puzzles me is why this hypothetical lightening only occurs at ground level, and why is it not a net generator of hydrogen…’

It is very dry on Titan so air moving across the surface could build up a local charge that could attract hydrogen molecules close to the ethylene molecules ‘droplets’ and act much like a catalyst to join them to form Ethane which collects in the seas.

Rob Henry April 3, 2014 at 18:19

Michael, if lightening is the answer then something big is missing from the picture you gave. It is hard to see electrostatic charge being sufficiently strong that the induced dipole-dipole attraction concentrates the hydrogen sufficiently – especially since this would work many times better for traces of polar molecules such as ammonia, and H2 would disperse through diffusion four times as quickly as nitrogen (that makes up the bulk of the atmosphere). Unlike fire, where much oxygen gas is dragged past the same reductant by convection, this lightning should have one shot with its marginally enriched H2. If you can refer me to a paper I would love to see it, but I fear that this was just the product of raw brainstorming – just to see is any non-biological explanation might be remotely conceivable.

Michael April 4, 2014 at 15:47

@Rob Henry April 3, 2014 at 18:19


If say an Ethene droplets or other hydrocarbon was to fall through the atmosphere and it is dry there is the chance electrons would be removed from the droplets to build up a positive charge. A build up of charge will allow a discharge to occur ‘lightning’ which will create a high temperature plasma to which nearby hydrogen could be heated to form with the ethylene to form ethane.


Here is an article on hydrogen’s removal

Atomic and molecular hydrogen budget in Titan’s atmosphere


-At the bottom of the atmosphere, hydrogen is removed via the condensation of hydrocarbons and nitriles, as well as via the formation of heavy species (which have been labelled “soot” in photochemical models). The fate of these species is not tracked in the model but ultimately, they will either condense out of the atmosphere, or be incorporated in the material that forms the haze. In either case, they represent an irreversible loss of hydrogen to the surface.-

In part brain storming but the way you see it is life is doing the hydrogen removal when from the graphs multiple species of hydrocarbon are been removed at the same time as hydrogen is. This hydrocarbon removal may be in part due to condensation though, hard to tell (pressure and temp look reasonable for it to occur)

Another article points to a biotical present been negative

What Cassini-Huygens has revealed about Titan


-No biotic signatures have been found on Titan. One of the elements in the negative response (at least so far as the present or past life is concerned) was found by the GCMS in the 13C/14C isotopic ratio, which showed that no active biota exist on Titan and that the methane on Titan is of non-biologic source.-

Rob Henry April 4, 2014 at 20:47

When I google plasma and hydrocarbons I keep getting references as to how PRODUCE hydrogen gas. This is exactly as I expected for fundamental chemical reasons.

The C12/C13 ratio has always been a curly one. On Earth, life makes the atmospheric carbon heavier. This is seen on Titan, but methanogenesis gives a far more ambiguous isotopic signal than C3 or C4 production of CO2, and can go either way. The predominant expectation was for it to be depleted in C13, and it turned out to be notably enriched, so that is marginally suggestive of non-biological processes. To really get anywhere we need two different supplies of carbon, like atmosphere and sedimentary. To the best of my knowledge we don’t have that here.

Michael April 5, 2014 at 13:20

I was thinking more along the lines of minor electrostatic discharges between charged droplets as opposed to mega flashes. The droplets acting as catalyst sites.

Here is an article on about possible lightning on Titan


I will broach the question to some of my chemical engineering friends next week, they are much better placed than I.

ljk May 28, 2014 at 9:57

Hazy Sunsets on Titan Provide Clues to Atmospheres on Alien Exoplanets

By Paul Scott Anderson

Saturn’s moon Titan is one of the murkiest places in the solar system; its thick smog-like hydrocarbon haze in the upper atmosphere shrouds the entire moon, much like Venus’ perpetual cloud cover. Titan’s surface is completely hidden by this orange-ish haze, making it look rather bland and uninteresting. This unique environment may provide valuable clues to the nature of atmospheres on distant exoplanets however, according to new findings from scientists with the Cassini mission.

Even though Titan is a moon and not a planet, it is the most planet-like moon in the solar system with a dense nitrogen and methane atmosphere, and rain, rivers and lakes composed of liquid methane/ethane. It’s planet-like qualities make it an ideal case study for those exoplanets in other solar systems which may have similar conditions.

The scientists have developed a new technique, using Titan as a model for a possible exoplanet atmosphere, to understand how the haze in such an atmosphere could affect astronomers’ ability to study it. As Tyler Robinson, a NASA Postdoctoral Research Fellow at NASA’s Ames Research Center notes, “It turns out there’s a lot you can learn from looking at a sunset.”

The new research was published on May 26 in the Proceedings of the National Academy of Sciences.

Full article here:


ljk June 2, 2014 at 19:39

Whatever Happened To NASA’s Space Boat?


MAY 30, 2014, 2:22 PM

In 2009, the media was abuzz that NASA and ESA were considering the very first space boat — a floating vessel that would roam the lakes of one of Saturn’s moons. Unfortunately, the project lost out to a mission to Jupiter.

Then NASA teased us again in 2012. After considering 28 projects, the space agency settled on three finalists: a Mars probe, a comet hopper, and a space boat called Titan Marine Explorer (TiME). NASA chose the probe, crushing our dreams of extraterrestrial sailing.

Now NASA is again soliciting projects for their Discovery Program, but will TiME throw its name in the hat?

Full article here:


To quote:

“The best time to explore Titan’s seas, which are near Titan’s north pole, is in the early 2020s (during the end of the moon’s northern summer). During that time, the lakes are in daylight and a craft in them would be able to communicate directly with Earth without needing an expensive relay spacecraft,” Lorenz told Business Insider in an email.

The current application period would be “tight, but do-able,” said Lorenz, putting the craft on Titan in mid-2020s.

ljk June 24, 2014 at 13:23
ljk July 9, 2014 at 10:59

Titan’s Hidden Ocean Might Be as Salty as the Dead Sea

By Paul Scott Anderson

Saturn’s moon Titan is known for its methane seas, lakes, and rivers; surprisingly Earth-like in appearance yet distinctly alien at the same time. But there is also evidence for another ocean, this one of water, below the surface. Little is known about this hidden watery world, but now new results suggest it is likely very salty—as much as the Dead Sea on Earth.

The new results come from the study of data sent back by the Cassini spacecraft, which is still orbiting Saturn. They were published last week in the journal Icarus. Cassini obtained new information about Titan’s interior using gravity and topography data collected during the probe’s many flybys of the moon.

As Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory, noted, “Titan continues to prove itself as an endlessly fascinating world, and with our long-lived Cassini spacecraft, we’re unlocking new mysteries as fast as we solve old ones.”

The findings support previous models of Titan’s interior, of a rigid icy shell overlaying the ocean below. In order to explain the gravity data, researchers found that the icy shell must have a high density, most likely explained by very salty, briny water in the ocean. There is a good chance that this ocean is just as salty, if not more so, than the saltiest bodies of water on Earth, including the Dead Sea.

“This is an extremely salty ocean by Earth standards,” according to the paper’s lead author, Giuseppe Mitri of the University of Nantes in France. “Knowing this may change the way we view this ocean as a possible abode for present-day life, but conditions might have been very different there in the past.”

Full article here:


ljk September 5, 2014 at 10:41

Rainfall on Titan May Create Propane Aquifers, Study Suggests

By Paul Scott Anderson

Saturn’s largest moon Titan is a very alien yet eerily Earth-like world, with rain, rivers, lakes and seas; seen from above, the landscape has a familiar look to it. But those lakes, seas and rivers are fed by a different kind of rainfall – liquid methane/ethane. It is far too cold on the surface for liquid water, but the liquid hydrocarbons nicely fill in for H20 in Titan’s “water cycle.” Now, a new study shows how this rainfall interacts with and changes underground aquifers.

The study, led by Olivier Mousis, a Cassini research associate at the University of Franche-Comté in France, suggests that runoff from rainfall is chemically altered by icy materials called clathrates within the aquifers below the surface. These aquifers, composed of propane and ethane, then feed some of the lakes and seas on the surface, although the rainfall itself is thought to initially provide the liquid in most of them.


Full article here:


To quote:

Basically, there could be two different types of lakes/seas and rivers on Titan: those fed by underground springs would be composed of propane or ethane, while others formed from rainfall would still be composed primarily of methane.

The results provide important clues as to how the “methane cycle” on Titan works, and how it is both similar to and different from the hydrological cycle on Earth. It is worth noting also that Titan is also thought to have a liquid water ocean deeper down below the surface where it is warmer. It is unlikely that any of that water would ever make it to the surface, but like with other moons such as Europa and Enceladus, the presence of liquid water raises the prospect of possible life, at least microscopic.

Some scientists even think that life could be possible in the methane lakes and seas, but it would have to be well adapted somehow to that liquid yet freezing cold environment, if it ever originated to begin with.

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