News from Titan

[Colin Robinson]

Latest news from Titan

* Surface methane lakes not only at the poles
Tropical lakes on Saturn moon Maggie McKee at Nature.com
* Tidal bulging of Titan's bulk shape -- evidence for subsurface water ocean
Tides turn on Titan Sid Perkins at Nature.com
* Enigmatic surface erosion -- spindly river valleys, resembling those in areas on Earth recently affected by volcanos, glaciers.
River Networks on Saturn's Largest Moon at Science Daily

To sum up -- seems to be lots more liquid that previously known, more stuff moving about, recent re-shaping of surface...

I am reminded of David Grinspoon's "living worlds hypothesis": the view that a planet or moon which is geologically and meteorologically alive is more likely (than a less active world) to be alive biologically as well. There are a number of reasons this makes sense. The simplest reason is that geological and meteorological activity involves both liquids and flows of energy -- both important for life. There are also subtler arguments, to do with the way organisms and their environment shape one another (co-evolve)...

We still don't know whether there is life on Saturn's biggest moon. The question, for those interested in life beyond Earth, is whether Titan should get a closer look?

[primummobile]

Latest news from Titan

* Surface methane lakes not only at the poles
Tropical lakes on Saturn moon Maggie McKee at Nature.com
* Tidal bulging of Titan's bulk shape -- evidence for subsurface water ocean
Tides turn on Titan Sid Perkins at Nature.com
* Enigmatic surface erosion -- spindly river valleys, resembling those in areas on Earth recently affected by volcanos, glaciers.
River Networks on Saturn's Largest Moon at Science Daily

To sum up -- seems to be lots more liquid that previously known, more stuff moving about, recent re-shaping of surface...

I am reminded of David Grinspoon's "living worlds hypothesis": the view that a planet or moon which is geologically and meteorologically alive is more likely (than a less active world) to be alive biologically as well. There are a number of reasons this makes sense. The simplest reason is that geological and meteorological activity involves both liquids and flows of energy -- both important for life. There are also subtler arguments, to do with the way organisms and their environment shape one another (co-evolve)...

We still don't know whether there is life on Saturn's biggest moon. The question, for those interested in life beyond Earth, is whether Titan should get a closer look?

I think it should get a closer look just because it's there. But why do they assume that the global ocean is made from water?

[Noclevername]

I think it should get a closer look just because it's there. But why do they assume that the global ocean is made from water?

Per wikipedia,

Based on its bulk density of 1.88 g/cm3, Titan's bulk composition is half water ice and half rocky material. {snip}
Titan is likely differentiated into several layers with a 3,400 km rocky center surrounded by several layers composed of different crystal forms of ice.[22] Its interior may still be hot and there may be a liquid layer consisting of a "magma" composed of water and ammonia between the ice Ih crust and deeper ice layers made of high-pressure forms of ice. The presence of ammonia allows water to remain liquid even at temperatures as low as 176 K (−97 °C) (for eutectic mixture with water).[23] Evidence for such an ocean has recently been uncovered by the Cassini probe in the form of natural extremely-low-frequency (ELF) radio waves in Titan's atmosphere. Titan's surface is thought to be a poor reflector of ELF waves, so they may instead be reflecting off the liquid–ice boundary of a subsurface ocean.[24] Surface features were observed by the Cassini spacecraft to systematically shift by up to 30 km between October 2005 and May 2007, which suggests that the crust is decoupled from the interior, and provides additional evidence for an interior liquid layer.[25]

[primummobile]

Per wikipedia,

Wow. Guess I could have looked that up!

[mutleyeng]

I dont think there is a question about it being worth a look.
Unfortunately we have to prioritize.
Best as I can tell the astrobiologist hit list is
Mars (easiest rather than most likely)
Enceladus
Europa
Titan

[Colin Robinson]

I think it should get a closer look just because it's there. But why do they assume that the global ocean is made from water?

Per wikipedia,

Yes, it seems to be mainstream science that Titan's bulk composition is largely H₂O. The question has been how much if any of the H₂O is liquid rather than solid, and whether subsurface materials ever find their way to the surface thru cryovolcanism.

The Wikipedia article on Titan mentions arguments against existence of a subsurface ocean, developed by planetary geologist Jeffrey Moore. Moore argued in 2008 that Titan's interior is too cold for water to behave like lava, so the H₂O stays solid, and there are no current or recent cryovolcanos.

Since then Cassini has found a feature named Sotra Facula, which looks like a cryovolcano, but hasn't necessarily removed all doubts. The recent findings about tidal flexing are a further argument against Moore's model...

[Colin Robinson]

I dont think there is a question about it being worth a look.
Unfortunately we have to prioritize.
Best as I can tell the astrobiologist hit list is
Mars (easiest rather than most likely)
Enceladus
Europa
Titan

Each of these places has one or two features that make it interesting to astrobiologists.

However, Titan has a whole great list of interesting features: the organic chemistry taking place in the upper atmosphere, the methane lakes and rivers, water behaving like lava... Not to mention the evidence for stuff decomposing at or near the surface.

How can it belong at the bottom of your list?

[mutleyeng]

The order of my list is based on my assessment of priority I have heard from the astrobiologists. Chris mckay put it in that order, ive heard someone else swap a couple around, but 2 and 3 are always mentioned when asked where they want to go look. It dosnt mean minds cant have changed of course - but I can only base it on what i have heard.
I guess the others are thought could have conditions where life as we know it could exist. Titan would be something radically different.

[Selfsim]

Yes, it seems to be mainstream science that Titan's bulk composition is largely H₂O. The question has been how much if any of the H₂O is liquid rather than solid, and whether subsurface materials ever find their way to the surface thru cryovolcanism.

The Wikipedia article on Titan mentions arguments against existence of a subsurface ocean, developed by planetary geologist Jeffrey Moore. Moore argued in 2008 that Titan's interior is too cold for water to behave like lava, so the H₂O stays solid, and there are no current or recent cryovolcanos.

Since then Cassini has found a feature named Sotra Facula, which looks like a cryovolcano, but hasn't necessarily removed all doubts. The recent findings about tidal flexing are a further argument against Moore's model...

I'm back for a fleeting comment:
The first linked article by Maggie McKee says:

Besides Earth, Titan is the only solid object in the Solar System to circulate liquids in a cycle of rain and evaporation, although on Titan the process is driven by methane rather than water.

It goes on to speak of liquid methane forming liquid hydrocarbon 'lakes and seas' (ie: NASA's: Lunine and Griffith).

The second linked article quotes Lunine who speaks of tidal flexing, but again, he is only talking about liquid hydrocarbons … not liquid water.

The third article speaks only of liquid hydrocarbons carving out geological structures, similar to what water does on Earth. There is no evidence cited about liquid water.

As far as I know, there has never been any water directly detected on Titan. There was a reflectometry measurement done on a rock on the surface (by Huygens) which gave light reflection measurements consistent with ice … this is not evidence of water. There were no spectroscopic readings of water by Huygens, either.. as a matter of fact, absence of water in the spectra taken, requires further explanation.

AFAIK, the only 'evidence' of water is: (i) the planet density figure calculation, and; (ii) other indirect readings, which can sometimes infer the presence of water, but these do not rule out other explanations either. When last I looked, planetary density calculations do not constrain the conclusion to only water/rock mixtures. In the case of Titan, there still exists the possibility of the presence of subsurface hydrocarbons (liquid and/or clathrate-like compounds).

There is nothing mainstream about water existing on Titan. The problem seems to be the high frequency usage of the terms: 'rivers, lakes, seas and oceans', all of which conjure up the Earth-biased view of these being caused by water. This is mainly journo spin and, perhaps, frequently misinterpreted Astrobiologist speculations.

There is lots of spectroscopically confirmed water ice on other moons/rings, within the vicinity of Titan (eg: Enceladus), but this does not mean that Titan retains any significant water, in any particular state.

Regards

[Colin Robinson]

The order of my list is based on my assessment of priority I have heard from the astrobiologists. Chris mckay put it in that order, ive heard someone else swap a couple around, but 2 and 3 are always mentioned when asked where they want to go look. It dosnt mean minds cant have changed of course - but I can only base it on what i have heard.

At the Astrobiology Science Conference 2010, they had a debate on the topic "Titan versus Europa - Potential for Astrobiology".

I guess the others are thought could have conditions where life as we know it could exist. Titan would be something radically different.

Yes, that has been the argument. But it's based on the premise that Europa and Enceladus show more evidence of subsurface liquid water, compared to Titan. If Titan had no liquid water, then yes, any life there would have to be rather different from Earth life, in that all living things on Earth use liquid water as their solvent. But now evidence is increasing that Titan actually does have liquid water beneath its surface, why would life there need to be to be any more radically different than life on/in Europa or Enceladus?

[Colin Robinson]

I'm back for a fleeting comment:
The first linked article by Maggie McKee says:
It goes on to speak of liquid methane forming liquid hydrocarbon 'lakes and seas' (ie: NASA's: Lunine and Griffith).

The Maggie McKee article, linked from the opening post, is about liquid hydrocarbons, yes. Did anyone suggest otherwise?

The second linked article quotes Lunine who speaks of tidal flexing, but again, he is only talking about liquid hydrocarbons … not liquid water.

The second linked article, from Nature.com, is Sid Perkins' summary of very recent work by Luciano Iess, a planetary scientist at the Sapienza University of Rome. The article states:

Data gathered by NASA’s Cassini probe as it repeatedly swept past Titan, Saturn’s largest moon, offers the best evidence yet that the smog-swaddled satellite has a substantial ocean of water sloshing beneath a thick icy crust.

The third linked article makes the following comparison between terrain on Titan and on Earth.

Black compared Titan's images with recently renewed landscapes on Earth, including volcanic terrain on the island of Kauai and recently glaciated landscapes in North America. The river networks in those locations are similar in form to those on Titan, suggesting that geologic processes may have reshaped the moon's icy surface in the recent past.

No-one doubts that Titan's surface has been eroded by methane rivers. However, that does not explain the similarities with Kauai volcanic terrain and with North American recently glaciated terrain. Geologically recent cryovolcanism (H₂O behaving like a cross between a lava flow and a glacier) is a likely explanation...

When last I looked, planetary density calculations do not constrain the conclusion to only water/rock mixtures. In the case of Titan, there still exists the possibility of the presence of subsurface hydrocarbons (liquid and/or clathrate-like compounds).

Do you mean compounds like methane clathrate, which consists largely of H₂O? If not, what specifically do you mean?

[John Jaksich]

I am unsure if anyone has mentioned it, but subsurface methane and water--> may result from physco-chemical processes rather than a biological role----> water under the subsurface may take part in a "pseudo" Fisher-Tropsch synthesis with Carbonates under the surface. So, in short, hydrocarbon lakes are formed through a seepage of "hydrocarbons" from under the "hard" crust. They "may" subsequently solidify or become "rain" --based upon so-called local conditions.

My personal readings tell me that some of this is good science---but much more needs to be done so it may be confirmed or thrown out as "wrong".

[Selfsim]

The Maggie McKee article, linked from the opening post, is about liquid hydrocarbons, yes. Did anyone suggest otherwise?

No. But your question is premature as it presumes the presence of sub-surface water … which is far from a 'given' piece of 'mainstream science' ...

The question has been how much if any of the H₂O is liquid rather than solid, and whether subsurface materials ever find their way to the surface thru cryovolcanism.

...

The second linked article, from Nature.com, is Sid Perkins' summary of very recent work by Luciano Iess, a planetary scientist at the Sapienza University of Rome. The article states:

Data gathered by NASA’s Cassini probe as it repeatedly swept past Titan, Saturn’s largest moon, offers the best evidence yet that the smog-swaddled satellite has a substantial ocean of water sloshing beneath a thick icy crust.

This is what Sid Perkins is saying … not what the scientists who did the study are saying.

No-one doubts that Titan's surface has been eroded by methane rivers. However, that does not explain the similarities with Kauai volcanic terrain and with North American recently glaciated terrain. Geologically recent cryovolcanism (H₂O behaving like a cross between a lava flow and a glacier) is a likely explanation…

The term 'Cryovolcanism' is not limited exclusively to water flows, and it in no way can be used to infer that liquid water has caused the erosion. Anything liquid under those conditions, could have caused the erosion … and does.

Do you mean compounds like methane clathrate, which consists largely of H₂O? If not, what specifically do you mean?

No .. I mean what I said … Clathrate-like compounds.

A clathrate hydrate, in particular, is a special type of gas hydrate in which a lattice of water molecules encloses molecules of a trapped gas.

.. that's not the only clathrate compound.

Colin .. I'm not going to argue further with you about this.
Titan is an interesting moon, and is a good candidate to study in order to find out how other compounds behave on a moon having 0.14g, -180^oC, and an active atmosphere.

[John Jaksich]

I thought I would throw this into the fray---->

Here is the latest proposed (schematic) model for Titan: (Credit for schematic is : A. Tavani---NASA)

[Selfsim]

I thought I would throw this into the fray---->

Here is the latest proposed (schematic) model for Titan: (Credit for schematic is : A. Tavani---NASA)

Hi John;
Is there more to this than an artist's graphic ? Who/what is A. Tavani ?
(References please ?).
Cheers

[Colin Robinson]

This is what Sid Perkins is saying … not what the scientists who did the study are saying.

OK, here is a link to a NASA press release, with a direct quote from the scientist who led the study
Cassini Finds Likely Subsurface Ocean on Saturn Moon

Data from NASA's Cassini spacecraft have revealed Saturn's moon Titan likely harbors a layer of liquid water under its ice shell...
"Cassini's detection of large tides on Titan leads to the almost inescapable conclusion that there is a hidden ocean at depth," said Luciano Iess, the paper's lead author and a Cassini team member at the Sapienza University of Rome, Italy. "The search for water is an important goal in solar system exploration, and now we've spotted another place where it is abundant."

Colin .. I'm not going to argue further with you about this.

Selfsim, if you wanted to demonstrate that Titan doesn't have subsurface liquid water, it's not me you'd need to argue with, it's Luciano Iess and his colleagues...

[Colin Robinson]

I am unsure if anyone has mentioned it, but subsurface methane and water--> may result from physco-chemical processes rather than a biological role----> water under the subsurface may take part in a "pseudo" Fisher-Tropsch synthesis with Carbonates under the surface. So, in short, hydrocarbon lakes are formed through a seepage of "hydrocarbons" from under the "hard" crust. They "may" subsequently solidify or become "rain" --based upon so-called local conditions.

My personal readings tell me that some of this is good science---but much more needs to be done so it may be confirmed or thrown out as "wrong".

John, I'd basically agree with you that methane could be produced by chemical reactions beneath the surface, and later seep up into the surface lakes and the atmosphere... Or maybe no chemical reaction was needed, because there has been methane in some form inside Titan since Titan was formed.

This is not necessarily an argument against Titan having biology, though.

The crucial question is not how the methane got there, but what happens after photolysis reactions in the upper atmosphere turn some of the methane into other, more complex organic compounds. Does something happen that breaks down (decomposes) those more complex organics back into methane again? There is some reason to think so -- to begin with, the first thing Huygens found when it landed, was much less ethane on Titan's surface than predicted by a model without any decomposition...

It is also true that break-down of complex organics, if it is in fact occurring, could be due to a non-living catalyst. It is difficult to distinguish on chemical grounds between an organism and a catalyst, because, looked at from a chemical point of view, metabolism is catalysis.

Nonetheless, if you are looking to find live microbes, a mass of decomposing organic material is the logical place to look.

[John Jaksich]

Hi John;
Is there more to this than an artist's graphic ? Who/what is A. Tavani ?
(References please ?).
Cheers

As with all NASA images--it falls within the public domain. I don't personally know the illustrator, but it is (?) safe to assume that he/she works for NASA.

The article and associated website are:


http://www.nasa.gov/mission_pages/ca...i20120628.html


Further information can be found at:


http://www.nasa.gov/cassini




or




http://saturn.jpl.nasa.gov/

[mutleyeng]

Yes, that has been the argument. But it's based on the premise that Europa and Enceladus show more evidence of subsurface liquid water, compared to Titan. If Titan had no liquid water, then yes, any life there would have to be rather different from Earth life, in that all living things on Earth use liquid water as their solvent. But now evidence is increasing that Titan actually does have liquid water beneath its surface, why would life there need to be to be any more radically different than life on/in Europa or Enceladus?

All i can say is should the mainstream consensus consider this to be the case, then sure, Titan will have a stronger case. Practicality also comes into the equation though. Enceladus has what seems to me to be a huge advantage that it is venting its guts from dirty great cracks in the ice. That makes it a more likely target than Europa for me. So far as Titan is concerned, if the case is made then I am all for it

[Colin Robinson]

All i can say is should the mainstream consensus consider this to be the case, then sure, Titan will have a stronger case.

Luciano Iess' findings about the tidal flexing and the subsurface water ocean have been published in the mainstream journal Science.

Practicality also comes into the equation though. Enceladus has what seems to me to be a huge advantage that it is venting its guts from dirty great cracks in the ice. That makes it a more likely target than Europa for me.

Yes, Enceladus still offers us that advantage -- it has the most accessible body of liquid water beyond Earth...

[mutleyeng]

Luciano Iess' findings about the tidal flexing and the subsurface water ocean have been published in the mainstream journal Science.
.

Thats not the same thing as being the mainstream consensus. Time will tell on that

[Selfsim]

What we have here, (with Iess et al), is a team which has developed a working model. I have no problems in reviewing a working model with a critical eye .. and in this case I don't care what the qualifications are, of those who developed it. In this case, the issue is: 'Where/what is the evidence ?'

At present, the evidence for an internal liquid water ocean is circumstantial. Having said this, the development of a model which does have a liquid water ocean, is as good as any other circumstantially based model constrained by the same physical parameters measured by Cassini, Hubble, Huygens, Keck, ESA scopes etc.

IMO, a working planetary model, which targets an explanation for the makeup of a remote moon, does not justify the use of definitive terms implying that it represents reality. I feel strongly suspicious that Iess' model serves the sole purpose of swaying opinion in the direction that would result in the further exploration of Titan, and I don't buy it.

In the absence of independently verifable, direct spectroscopic measurements of water at or on the surface, its scientific implications as far as prebiotic Earth-like life are concerned, are zilch. Even if this were detected, it still means zilch scientifically (life-wise), but data gathering via exploratory probes, is the only way we can move the issue along, so it makes sense to proceed with probe missions in the future.

Having said all of this, it also seems strange that the heated Huygens probe, did not result in the vaporisation of, and subsequent detection of, surface cryovolcanic by-products (such as the hypothesised water). The spectroscopic data retrieved from Huygens, showed absolutely no signs of the presence of surface water, in any detectable quantities (!).

If interested in the scientific side, for a good summary on how the various environmental cycles are thought to work on Titan, which fairly denotes the various unknowns, see here. (Note that spectroscopically measurable water vapour exists in the stratosphere .. but that's not surprising, given the amount of water being ejected by Enceladus, and other Cassini-detected water within the general vicinity).

Cheers

[Noclevername]

I feel strongly suspicious that Iess' model serves the sole purpose of swaying opinion in the direction that would result in the further exploration of Titan, and I don't buy it.

And how are we going to find evidence for/against anything without further exploration?

[Selfsim]

And how are we going to find evidence for/against anything without further exploration?

Titan is an interesting moon, and is a good candidate to study in order to find out how other compounds behave on a moon having 0.14g, -180oC, and an active atmosphere.
...
… so it makes sense to proceed with probe missions in the future.

I agree with the exploration of Titan to gather more data ... (and always have) !!
Regards

[Colin Robinson]

At present, the evidence for an internal liquid water ocean is circumstantial. Having said this, the development of a model which does have a liquid water ocean, is as good as any other circumstantially based model constrained by the same physical parameters measured by Cassini, Hubble, Huygens, Keck, ESA scopes etc.

When you say "any other model"... Is there some "other model" that fits the observed facts just as well?

You've repeatedly suggested that Titan may not have water in any form, liquid or solid, except for a bit of atmospheric vapor due to some external source.

What I'd like to know, is whether anyone has developed a radically waterless model of Titan's internal structure – a model with neither liquid water nor water-ammonia mixtures, nor water ice, nor clathrates based on water ice? Is there published scientific literature that sets out such a model? If so, when was it published, and by who?

[Selfsim]

Well, here's an interesting version of the relevant press release .. I really wish I could get a copy of the Iess paper to find out exactly the logic leading to the conclusion of a specifically water ocean .. unfortunately its behind a paywall.
In the meantime he's an interesting quote by Lunine (from the above release ...):

Spacecraft data show Saturn creates solid tides approximately 30 feet (10 meters) in height, which suggests Titan is not made entirely of solid rocky material; in fact, “[...]the density of Titan is consistent with a body that is about 60% rock and 40% water,” says planetary scientist Jonathan Lunine, of Cornell University, one of the co-authors of the paper. “The ocean must be fairly thick — a few hundred kilometers. And it must lie relatively close to the surface — beginning no farther down than 100 kilometers.”

Of course, it doesn’t necessarily have to be water; computations so far show the presence of a subterranian liquid. For all we know it could very well be covered in methane, however water is the most solid bet.

Notice how now its a 'bet' that its water ?? ...

“It’s a matter of what’s abundant in the solar system,” Lunine says. “Water is far and away one of the most abundant substances. Europa, as well its sister moons Ganymede and Callisto are covered with water ice like Titan. Rock and metals are similarly plentiful. All this hangs together to suggest what the interior of Titan is like.”

So, now its suddenly become generalised ... and non-specific to Titan ...

Life on Titan

Water, in liquid form, is the first thing scientists are looking for when investigation for signs of extraterrestrial life.

So, ET searchers may just have 'water-the-brain', eh ?

In this case, on Titan the presence of a subsurface layer of liquid water is not itself an indicator for life. Scientists think life is more likely to arise when liquid water is in contact with rock, and these measurements cannot tell whether the ocean bottom is made up of rock or ice. The results have a bigger implication for the mystery of methane replenishment on Titan.

So, as I've said ... a water core is not compulsory !!

I accept that the model they've created might be consistent ... I'd prefer to read their paper before commenting further on that aspect ... but a consistent model doesn't necessarily provide strong ties back into the real-world (in this case, the real Titan).

It has only been suggested that clathrate hydrates may trap missing sequestered carbon beneath the surface .. but that's only a suggestion. There are other explanations and mechanisms which can also explain how this can happen ... and could also account for the tidal flexing/movements ... and, perhaps, the overall planetary density figure.

This just doesn't look like a slam-dunk to me !

Cheers

[Colin Robinson]

Well, here's an interesting version of the relevant press release .. I really wish I could get a copy of the Iess paper to find out exactly the logic leading to the conclusion of a specifically water ocean .. unfortunately its behind a paywall.
In the meantime he's an interesting quote by Lunine (from the above release ...):
Notice how now its a 'bet' that its water ?? ...

Well, it is not exactly "a version of the press release", it's an article partially based on the press release. The journalist's name is given as Tibi Pulu. And most of the parts which you've bolded and underlined from your "quote by Lunine", including the word "bet", are actually the journalist's words rather than Lunine's.

True, it was Lunine who said: "All this hangs together to suggest what the interior of Titan is like."

Theories about the insides of any planet or moon are naturally going to be based on indirect evidence, unless there is actually stuff gushing out of the surface, as on Enceladus. Europa, on the other hand, does not have stuff gushing out like that. Therefore, even if a subsurface ocean in Europa is considered highly probable, its existence and composition are less certain than in the case of Enceladus.

The point that the bottom of Titan's subsurface ocean may consist either of rock or of ice, fits with Lunine's statement that "the density of Titan is consistent with a body that is about 60% rock and 40% water".

So, now its suddenly become generalised ... and non-specific to Titan ...

Lunine's point about the overall abundance of water in the solar system will only seem relevant to those who think the whole solar system emerged from a single accretion disk. But where is the planetary scientist who thinks otherwise?

There are other explanations and mechanisms which can also explain how this can happen ... and could also account for the tidal flexing/movements ... and, perhaps, the overall planetary density figure.

It is easy to talk vaguely about "other explanations and mechanisms"... But where in the scientific literature are these "other explanations" to be found?

[Selfsim]

When you say "any other model"... Is there some "other model" that fits the observed facts just as well?

You've repeatedly suggested that Titan may not have water in any form, liquid or solid, except for a bit of atmospheric vapor due to some external source.

What I'd like to know, is whether anyone has developed a radically waterless model of Titan's internal structure – a model with neither liquid water nor water-ammonia mixtures, nor water ice, nor clathrates based on water ice? Is there published scientific literature that sets out such a model? If so, when was it published, and by who?

Not that I'm aware of .. but so what ? It has been suggested that the martian gullies in the southern hemisphere of Mars, might have been formed by liquid carbon dioxide flows, rather than water .. which kind of demonstrates another geological mechanism not familiar to us, which might be at play in the different physical environment there.

In the case of Titan, it has also been suggested that a reservoir of carbon in its original form (organic compounds, carbon dioxide and grains) that is still being converted to methane, might exist far below the surface ('The abundances of constituents of Titan's atmosphere from the GCMS instrument on the Huygens probe'. Niemann, H. B. et al. Nature 438, 779–784 (2005)). This particular idea is not favoured over the clathrate mechanism I might add, (due a lack of supporting evidence of other detailed mechanisms), but it hasn't been ruled out either.

I do not question the abundance of water ice at/around the Saturnian environment .. I also don't have a problem with clathrates being suggested as a plausible mechanism involved in the tidal flexing of Titan. The formation of clathrate hydrates in the 'feeding' zones of the ice giants depends on the efficiency of the trapping of volatiles by microscopic icy grains. Whether this is applicable on a wide scale in the case of Titan, is unknown. What I do question is the strong declaration that Iess' story is real, exists for certain, and that all other alternatives have been ruled out. We simply don't have sufficient data to do that. Having a consistent solar system planetary formation theory, which makes a testable prediction of deformable methane based clarates residing at the core of Titan, is also not an issue.

My point is that if we are truly interested in exploration, we need to focus on keeping an eye out for geological mechanisms we haven't observed before. If we dwell too heavily on things observed on Earth, (.. like clathrates ... which formed because of physical conditions applicable on earth or its location and/or physical environment within the Solar nebula), I don't see how we'd ever see these other mechanisms and further scientific knowledge (?)

Another example: (and somewhat off-topic), just yesterday, I was reading about giant avalanches on Iapetus, whose runoff distances are out of proportion with the heights of the material falls. Frictional forces between the particles in a low gravity, extremely cold environment have formed the basis of a testable hypothesis. I'm sure there will be many other physical phenomena we haven't seen yet, but nonetheless still occur, and may or may not be common in a given search space.

Cheers

[Colin Robinson]

When you say "any other model"... Is there some "other model" that fits the observed facts just as well?

You've repeatedly suggested that Titan may not have water in any form, liquid or solid, except for a bit of atmospheric vapor due to some external source.

What I'd like to know, is whether anyone has developed a radically waterless model of Titan's internal structure – a model with neither liquid water nor water-ammonia mixtures, nor water ice, nor clathrates based on water ice? Is there published scientific literature that sets out such a model? If so, when was it published, and by who?

Not that I'm aware of .. but so what ?

Let's backtrack a little...

A few days ago, I wrote:

Yes, it seems to be mainstream science that Titan's bulk composition is largely H₂O. The question has been how much if any of the H₂O is liquid rather than solid, and whether subsurface materials ever find their way to the surface thru cryovolcanism.

To which you objected

There is nothing mainstream about water existing on Titan.

If you had been able to back up your objection, by showing me even one scientific publication which argues for a bulk composition of Titan without large amounts of water (in solid and/or liquid form)... then I would have had to revise what I said about the mainstream scientific view.

My point is that if we are truly interested in exploration, we need to focus on keeping an eye out for geological mechanisms we haven't observed before.

I agree that when studying other planets/moons, we need to be open-minded about unfamiliar forms of geology.

And unfamiliar forms of life?

[Selfsim]

I agree that when studying other planets, we need to be open-minded about unfamiliar forms of geology.

One of the more interesting discussions might be about the methane present there .. that report I linked to says:

The value of ¹²C/¹³C in methane provides no support for suggestions of an active biota on Titan. It takes less energy to form a chemical bond between two ¹²C atoms than between ¹²C and ¹³C, so complex organic molecules associated with biological processes on earth show an enrichment in ¹²C—the ¹²C/¹³C ratio is greater than the Pee Dee Belemnite (PDB) inorganic standard value of 89.9, and could be as high as 95. Therefore the assumption that such enrichment will occur in carbon-based non-terrestrial biology seems reasonable.

We do not find this enrichment in the methane of Titan. Instead, a geological source for methane, with a possible clathrate reservoir as storage in the interior of Titan is favoured.

.. Just goes to show that 'reasonable assumptions' don't make a lot of difference when it comes to actually measuring the reality of the situation, eh ?
Ie: in spite of the 'complex chemistry' of Titan, and in spite of theorised subsurface ammonia-water clathrates (and in spite of there being no measured water in the atmosphere or the surface), the measured methane also exhibits no sign of biogenic properties ...

They go on …

As occurs on Earth, serpentinization that releases hydrogen from water while oxidizing iron- or magnesium-bearing minerals could produce methane through a Fischer–Tropsch reaction of the H₂ with CO₂, or reduction of carbon grains in the crustal rocks in the interior.

… at least they are considering other than subsurface water-based clathrates, as a release mechanism for the methane, I suppose ...

And unfamiliar forms of life?

Now what might they be ?