Vienna conference 4 - Saturn's moons

[JonClarke]

TITAN<br /><br />Radar imagery of Titan has identified numerous cryovolcanic flows, fluvial features, tectonic features and a very small number of craters. The cryovolcanic flows are leveed, and the fluvial features debouche onto lowland fans and deltas<br /><br />The Huygens descent imaging has been processed, resulting in better images, although rectification is proving a slow job. The highlands are significantly brighter and redder than the lowlands, which were called lake beds by several speakers. The presence of episodic methane fluvial activity was also well accepted. Theoretical modeling of methane-ethane liquids and their ability to transport clasts of the 8-10 cm size seen at the landing site under Titan gravity has been carried out. The results indicate that flow velocities of 1 m per second are required, which are quite reasonable. The atmospheric sonar indicated that the highland areas consist of two distinct levels, this might consist of small buttes or mesas over a lower surface. There is about 8 m difference in elevation between the two.<br /><br />There was an interesting review of the astrobiological implications of the discoveries on Titan by Raulin et al. The main implications discussed were planetary organic geochemistry, the origin of terrestrial life, and the search for extraterrestrial life. Some of the major points I noted was that there is a high probability of a subsurface water-ammonia ocean. Carbon isotope ratios measured were all in the inorganic range, as expected. High molecular weight C-N compounds were detected, with up to 7 carbon atoms, these are the tholins predicted by Sagan many years ago. It is worth noting that the formation of tholins by inorganic processes can cause significant fractionation of light carbon into what is normally considered the biological range. As predicted theoretically, the tholins seem to be scavenged by methane range and transported to the surface. Overall atmospheric abundances indicate that th <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[silylene old]

Jon, very interesting.<br /><br />Particularly I note:<br />1) On Titan, you said some researchers believe in "a high high probability of a subsurface water-ammonia ocean."<br />- what is the reason for believing this?<br /><br />2) Interesting Iapetus theory for the equitorial ridge and the bright deposits.<br />- I think this points to the strong need for a close-pass high resolution imaging of the ridge.<br />- Is Iapetus big enough to support substantial global geyser system? And what is the heating mechanism?<br />- And what would be the venting fluid? It would certainly need to contain a huge amount of water to re-freeze, dissolved minerals, ash, or entrained loose rock. I find it hard to believe that there would be enough venting fluid to assemble a 10 km high equitorial ridge. This would imply a vast subsurface network of feeder tubes to the vents to bring up enough depositable materials.<br />- If the fluid volume was huge (it would have to be) Iapetus must have shrunk as much of the venting fluid entered the gaseous phase and got lost. Is there evidence for shrinkage wrinkles and ridges? <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[vogon13]

Any kind of internal activity at Iapetus is extremely unlikely. The rigidity of the crust, as demonstrated by the lack of 'settling' around the equatorial ridge, and also the dubiously describe 'faceting' argue strongly against any kind of internal warming sufficient to generate 'geysers' in the classical (and cryo version) sense. <br /><br />BTW, if you want to see facets, go look at Hyperion. Hyperion shows just how rigid these icy materials are at the temperature ranges in this part of the solar system.<br /><br />IMO, the dark 'staining' is best explained by temperature sensitive gaseous materials in the vicinity of Iapetus. Orientation of ridge structure on Iapetus may best be explained by tidal effects from distant Saturn braking Iapetus to a halt with 'big' end of ridge antipodal to sub-Saturn point. Insolation induced photo-darkening effects would be symmetrical to equator, regardless of presence on equator of ridge or not. <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[JonClarke]

Sorry silylene, I missed the talk on the interior ot Titan, but it was referred to in other talks. Some lines of evidence I can think of:<br /><br />Global thermal models going back to the 70's indicate that this is likely.<br /><br />Argon istopes showing radioactive heating.<br /><br />The lack of impact features and abundant cryovolcanism, point to an active interior.<br /><br />There may be some magnetic observations as well that support this (I suspect this was in the talk I missed).<br /><br />As to Iapetus,. it is an interesting theory, the issues to raise were not mentioned, but are certainly worth considering.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[bobw]

Thanks for the news reports Jon. About the modeling of liquid transporting clasts; is the 1 m/sec calculated using ice as the material being transported? <div class="Discussion_UserSignature"> </div>

 

[JonClarke]

Yes, all modelling was done under Titanian conditions - methane-ethane fluid viscosities and densities, water ice density, and gravity. Someone asked the same question at the presentation.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

The new descent image mosaics I saw are now up on the planetary society web site.<br /><br />http://www.planetary.org/news/2005/huygens_images_0505.html<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[yurkin]

silylene<br /><br /><b>VolcanoPele</b> had this to say about haveing a sub-surfaceocean in the Investigating Titan's Surface thread.<br /><br /><font color="yellow">To be honest, two arguments are possible. One is that as Titan a global sub-surface ocean, 300 km down, formed, but has not frozen. If Titan's global ocean froze, the eccentricity would be dissipated and the orbit would be circularized. The other possibility is that Titan did not differentiate very well and that it never had a global sub-surface ocean. Since there was no ocean to freeze, it couldn't dissipate the eccentricity.</font><br />

 

[silylene old]

Yurkin, I was hoping that Jon could tell us what new data from the conference leads some researchers to believe that there is a global sub-surface ocean. I still think it is interesting speculation, probably endlessly debatable.<br /><br />But your post sums it up well nonetheless. <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[JonClarke]

However I would read the argon isotope ansd physiography data as suggesting that there has been strong radiactive heating and therefore there has been internal heating and differentiation.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[jmilsom]

It is great to see some of the people studying Iapetus to finally release some official findings. In my contributions to the Iapetus thread (the serious one!), I speculated that the two phenomena (light-dark areas and ridge) must be linked in some way. One bizarre phenomenon OK, but two on the same moon? Too large a coincidence. If it really is NOT of extenal origin - that blows most of the leading theories out of the water!!! Is it really beyond any doubt that it is of internal origin? This should really trigger the debate again - look forward to reading it. <br /><br />Re: all the new data on Titan. It realy is amazing. The information gained to date will support research for many years to come. <div class="Discussion_UserSignature"> </div>

 

[jmilsom]

<font color="red"> Hey Vogon13, </font><br /><br />What happened to all the serious Iapetus work (as opposed to the junk Artificial Construct threads)? Have you got access to the full paper that Jon summarises? If these guys have proven beyond any doubt that the dark areas are of endogenic origin, it blows most our theories and discusssions out of the water. A most unexpected finding. <br /><br /><font color="yellow"> The dark material on Iapetus is not hemispherical, therefore is not of external origin. </font><br /><br />This reads like a conclusive statement, but I don't really understand it. Does anyone have more info.? <div class="Discussion_UserSignature"> </div>

 

[JonClarke]

My understanding of the argument is that if the dark material had been accreted onto the surface of Iapetus it would occur across the whole leading hemsiphere. However it is not, forming the broad band centred on the equator. I don't know enough about Iapetus to comment on this, I am only saying what I read <img src="/images/icons/smile.gif" /><br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[centsworth_II]

On the (serious) Iapetus thread, the theory was discussed that the dark band was the result of Iapetus gathering up material from a formerly existing ring. I didn't read the thread closely so I don't know the details. I don't even remember if it was a ring of Saturn or a ring of Iapetus being referred to. I wonder if this senario would get around the necessity of a "hemispheric" depositional pattern. I wonder if the possibillity of material from a no longer present ring was considered in the Vienna presentations? <div class="Discussion_UserSignature"> </div>

 

[volcanopele2]

The problem with the ridge being a source of the dark material is the difference in ages. The ridge itself is heavily crater and is likely quite old. The dark material is likely a recent addition to Iapetus' surface due to the very shallow depth of the dark material (crater should easily penetrate the deposit and none were seen). Radar results from Arecibo could not find a distinction between the bright and dark material, suggesting that the dark material is thin enough for radio waves to penetrate (a few meters at most).<br /><br />One theory I currently like is the one proposed by John Spencer of the CIRS team at LPSC in March. The CIRS and VIMS instruments found very little water ice within Cassini Regio. Spencer proposed that rather than the area being a deposit of dark material, Cassini Regio is an area where bright water ice material has been removed and transported poleward and trailing hemisphere-ward, leaving behind a dark lag deposit of dark carbonaceous material like cyanides. The little water ice that does exist within Cassini Regio appear on polarward facing slopes, similar to the effect seen on Callisto and Ganymede.

 

[centsworth_II]

<font color="yellow">"...bright water ice material has been removed and transported poleward and trailing hemisphere-ward..."</font><br /><br />I can see water ice being removed into space, but wouldn't transport from one location to another on the moon require an atmosphere? <div class="Discussion_UserSignature"> </div>

 

[vogon13]

Atmosphere on Iapetus more retainable than Enceladus. Easier in distant past, too, as sun dimmer in that epoch. <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[centsworth_II]

According to volcanopele2's post, "The dark material is likely a recent addition to Iapetus' surface...." Or seen the other way, the removal (and transport?) of water ice was recent. Is it really possible that there was a recent atmosphere? Would one be necessary for the transport of water that is proposed?<br /><br /> <div class="Discussion_UserSignature"> </div>

 

[vogon13]

Temporary atmosphere retention seems quite plausible now. Compare masses of Pluto, Triton, Iapetus, and Enceladus. For a material that is apparently just a coating on an icy surface, over the eons, even a very transient atmosphere would appear sufficient.<br /><br />Also, keep in mind the 'Teller Treshhold', regarding large impacts on Titan. Any impact releasing more than the equivalent of 100 megatons (more or less) (like that big Iowa sized crater on that radar trace on orbit whatever) will blow gas away from Titan at speeds over escape. Magnetotail of Saturn can transport gas to Iapetus realm every 80 days. Gas need only hang around long enough to tholinize and then stain surface.<br /><br />I'm thinking this reaction to be temp sensitive which would explain symmetry N-S of Iapetus equator and also, the specific progression of the pattern of the darkening in the crater bowls as you look further away from the equator. In northern hemisphere, northern arc of crater bowl is angled more perpendicularly to suns rays (and therefore warmer) and that's where the dark stain is more pronounced. You can tell how far north or south of the equator a crater is (if you don't already know) by how dark the poleward arc of the crater bowl is. <br /><br />BTW, don't use the over processed RCH pix, use the JPL pics.<br /><br />Also, the 'coating' has to be renewing itself. Paucity of fresh craters in dark area strongly implies process is on going.<br /><br />Excellent point regarding rugged cratering on the ridge. That sucker is ancient! The coating is fresh. Also, slides on equatorward crater bowls in places remain white. Local cold spot! Sun would not shine on these oblique surfaces so they stay cold. Reaction doesn't occur here, or is greatly slowed by the cold.<br /><br />Dark coating is like IR sensitive photo film. Turns dark in the heat, stays white in the cold. <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[JonClarke]

Either a ring or one of the other moons (I forget which one). The paper also mentioned the possibility that the ridge it self (which only extends a third of the circumgerence of Iapetus, was due to mantle convection. if so, I suggest that its preservation over a significant period of time pointing to a very rigid crust. As to the dark material being a yound deposit, I don't know. It does seem to be blanketing the topography in anyway, I suspect it is actually quite old.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>