An interesting quote from the website: http://www.titanexploration.com


"But one can also suggest that those streaks are the outcome of a subsurface ocean with eastward currents that would create fractures or grooves in the icy crust of Titan. Hence, that would also explain, for instance, why the dark streaks have the same direction as most of the ridges in their environment."

The above is a great website resource btw. Just found it today. Since I have posted before that I do not believe that the features that we are seeing on radar are actual linear dunes - I was very excited to read that someone else may feel the same.

I mentioned before in prior posts that believe that the dark areas seen on radar and by Cassini are indeed oceans of methane with possible traces of ammonia and other hydrocarbons. The reason that we are not seeing any "specular" glints may be due to complex chemical interactions between the surface of any ocean and the atmosphere. A complex hydrocarbon "crust" my not be out of the question.

This quote interests me as well: "Titan's surface reflected no more than 15 percent to 20 percent at infrared light wavelengths. Light reflected revealed there are organic materials and water ice but also water ice laced with an unknown constituent."

What exactly is the surface of Titan made up of. Interestingly, acetelyne was not found (although it is found in the atmosphere). Where is the acetelyne ending up if not on the surface?

Well, judging by that rabbit, the surface is made up of frozen rabbit poo. It's what rabbits do best (apart from the other thing). Seriously, though, why oh why choose a rabbit to show us what Titan looks like? My mind has boggled!

Bob Shaw

I remember a lot of use of the word ethane when speculating about what Titan's surface could consist of. Any chance the unknown constituents being ethane?

Or perhaps some form of Titanian methane moss/lichens?

One possibility is that the solid acetylene that settles on the surface (and you're right: there should have been a LOT of it) is chemically transformed into polymers -- one of which happens to be benzene. Now, benzene's boiling point is no less than +80 deg C (it doesn't even melt until +5.5 deg C), so the fact that Huygens' GCMS detected what looks very much like traces of it vaporized by the heated GCMS sample port -- which probably wasn't touching the surface -- suggests that there may be a LOT of benzene on the surface (and also a lot of cyanogen, which doesn't boil until -21 deg C but which was also apparently detected in gaseous form after landing). It may be that virtually all the acetylene that has drifted at a glacially slow pace down onto the surface over the eons has since been chemically transformed into benzene and other complex hydrocarbons.

And, yes, Huygens did also confirm the existence of ethane vapor after landing, confirming that there is some liquid ethane there -- but we already have good near-IR spectra of that stuff. I suspect the Mystery Compound is some complex hydrocarbon and/or nitrile that forms out of the settling smog AFTER it touches the surface.

My eyes!!! That web site is so...... 1997.

This all leads me to posit that now that we've finally flown a microphone as a planetary probe instrument, to find out what it sounds like on Titan, we should send an electronic nose to find out what it *smells* like. I'm imagining gasoline on compost/dung.

Well, if I remember correctly, the "smell" of gasoline -- like that of natural gas -- is entirely a product of the mercaptan added to it to enable humans to determine when there are dangerous concentrations of its vapor at hand. By itself, it has none. (But wasn't benzene what they used to use in moth balls? Nor must we forget the likely HCN on the surface, and its almond smell.)

The closest thing to an electronic nose we have would be a mass spectrometer for compelx organics, which could then be mixed in an appropriate ratio back on earth.

The moon smells of gunpowder, some meteorites smell of sulphur.

Doug

Naphtha, Bruce?

Phil

Phil:

Not on the naptha again are you? And you'd been so good since last time...

...still it explains the compulsive panoramas!

Bob Shaw

Heptane, Octane, Benzene - all have unique and very discernable odors. Benzene is quite sweet. The colors we are observing on Titan are NOT consistent with the bandwidths one would normally associate with benzene (which would be white or colorless) derivatives. These would tend to much darker - high absorbance in reds and yellows, green to purple reflectance, if any.

Benzene was also detected high in the upper atmosphere so it is quite logical that it should have rained down to the surface. So where is all the acetelyne?

Interestingly, benzene is a precuser to amino acid formation. Amino acids have also been detected in cold interstellar clouds as well as complex sugars. Did the instruments on Huygens have the ability to detect amino acids and sugars? Have these possibly combined over the last four billion years to create proteins?

The surface seems to appear quite spongy in the photo's. The pentrometer noted a crusty surface and a muddy subsurface. How different was the surface composition from the subsurface? Grains of water ice (like grains of sand) were identified below the crust but they were not mentioned as being detected at the surface.

Its hard to tell for now, but If the cat scratches are oceanic fractures then they are doing a very good job of looking just like sand dunes to Cassini's radar.

There didn't appear to be much powdery material at the Huygens landing site for the wind to blow around. It looked damp and muddy. But there are plenty of cat scratches north and south of the Huygens landing site.....

Those two dark linear features visible to the north in Huygens mosaics.....are they not cat scratches?

The original resistance of the 'crust' is now thought to be because the penetrometer initially hit a small pebble and then glanced off. (I even read one source that said the penetrometer might have been bent in the process.) The whole issue is a little cloudy, because the penetrometer event lasted at least 250 milliseconds; whereas all three of the 'axial' accelerometers recorded a landing event that lasted less than 150 ms(??!!).

The early descriptions said water-ice was detected on the pebbles, along with an unknown substance. To the best of my knowledge, the ratios have never been publically quantified.

Sugars have a Hydroxyl peak in the same spectral range as water, although it is not normally as broad, so they should be detectable. It has been mentioned that Huygens should have been able to detect ammonia, but I don't know if this was through GCMS or spectrascopically.

I agree Matt, at least on radar - they do look like dunes. However, due to the nature of the surface (it also really did seem damp and muddy to me as well), very slow windspeeds at the surface, no noticeable dark particulate deposits anywhere (airborne particulates do accumulate at a depth of a micron per year or so), no small dark windblown deposits around the water ice pebbles, etc. I think that what is being seen on the radar is due to a more exotic process.

But if I am wrong - I will be the first to admit it.

Thanks Messenger,

The strange thing about Titan's ammonia is that both Cassini and Huygens have failed to detect it in either the atmosphere or on the surface. It should be there (even as a solid) as ammonia would be the most likely source of nitrogen in Titan's atmosphere.

This is just one of the strange enigma's that have not (to my knowledge) been explained.

The DISR images clearly indicate the probe was tipping, swaying, involved in complex motions of some kind, just before the landing. The local Doppler Wind experiment was lost, and the VLA data reported to date still has an uncontrolled degree of freedom, along with a lot of noise. What I am getting to, is even with the data in hand, we cannot conclude the windspeed on the surface is weak. On the other hand, we do not see is any evidence of dust storms or surface activity of any kind -yet- , so the 'dunes' are difficult to explain.

I haven't seen anyone else who thinks that there was any evidence whatsoever of high near-surface winds during Huygens' landing; it was swerving around a bit, but not rapidly. But the winds, combined with the high atmospheric density, are quite high enough to generate the kinds of dunes seen, especially when you consider the fineness of the smog particles.

Bruce, I didn't say I think surface winds are high (I don't), I only stated that the motion of Huygens near the surface was peculiar, and we just do not know. I am a little surprised that we have not observed any particulate motion on or near the surface, so I wonder if the 'dunes' are active, or frozen - like the surface of Venus appears to be. Hopefully, Cassini will find out.

The fact that nothing moved is not surprising. The resolution of the DISR was not sufficient to see sand grains. In addition, RADAR shows that there were no dunes right near where Huygens landed though there were a couple about 20-30 km away.

In terms of winds, remember, longitudinal dunes are aligned with the average prevailing wind direction. I think I should a crude cartoon of this earlier. Basically, the wind can be coming out of any direction and speed at any given time, but on average, the strongest and/or most prevalent winds come out of the west, based on the orientation of the dunes and the way they interact with topographic highs. Their morphology both as linear features and their morphology around toopographic highs provides convincing evidence (to me at least) that these features are longitundinal dunes, not something produced from oceanic features.

Again, I suspect that it's been turned into acetylene polymers by now -- of which benzene is one of the most predominant. I think it worth noting, though, that when you actually look at the graphs of GCMS measurements in Hasso Niemann's Dec. 8, 2005 "Nature" article( http://sci.esa.int/science-e/www/object/in...fobjectid=38427 , Figure 1c), it seems hard to rule out the possibility that the GCMS DID detect some acetylene -- or ammonia, or HCN. These are not mentioned in Niemann's article, which says only that ethane was firmly identified on the surface; benzene, cynaogen and CO2 have been "tentatively identified"; and that work to identify other surface constiuents is continuing.

It may be that the exposure of Titan's surface to solar UV over long periods explains the absence of all these, to the extent that they actually are absent -- it can break down NH3 very efficiently, and it turns both C2H2 and HCN into polymers.

Bruce, check this out:

http://www.lpi.usra.edu/meetings/lpsc2006

Go to the Titan presentation.

This has got to be the most ambiguous presentation that I have ever read. I really get the feeling that the principal scientists have no idea what is being seen on the surface of Titan and what the surface composition is. Also after researching the SAR specs - apparently, the SAR can penetrate the surface by as much as 3-7 meters in some instances. I wonder if this has any bearing at all as to what is actually being visualized,

?, are you refering to Ralph Lorenz's abstract on the longituninal dunes? The evidence seems pretty unambiguous to me. True, there is a lot we don't know about Titan and there are plenty of interpretations that are ambiguous at best. I'll be the first to admit that our "lake", Ontario Lacus, is a perfect example of this. But I think the evidence regarding the longitudinal dunes (as well as fluvial channels of various styles) is pretty clear cut. Like it or not, it is becoming increasingly clear that the dark equatorial regions are not oceans, but great dune seas.

As to the ability to see the subsurface, that does play a role. For example, there are area on the boundaries of bright features where RADAR SAR shows dark dunes ontop of bright terrain. In ISS and VIMS, these areas appear dark. The can be reconciled if the depth of the dark particulate gradually decreases near the bright/dark boundaries. Eventually, the dark material between the dunes becomes thin enough that RADAR can penetrate it, revealing the bright material beneath. At near-IR wavelengths, these boundary regions appear dark, as both the dunes and the material beneath are likely thicker than a few microns.

I haven't had a chance yet to look at the Titan abstracts (I'm currently slogging through the huge amount of Mars stuff) -- but Elizabeth Turtle told the COMPLEX meeting that the evidence that "Ontario Lacus" is actually a liquid lake is extremely ambiguous. All the current images can tell us so far is that its edge is no sharper than those of many paterae on Io.

This morning I found some SAR images of Earth. Some of these images look very similar to what is being seen on Titan (especially the shoreline). Here is what I have come up with:

Ocean SAR Images

http://www.ifm.uni-hamburg.de/cleanseas/examples/cs_sar.htm

http://www.jpl.nasa.gov/radar/sircxsar/sc-oilsk.gif

http://www.jpl.nasa.gov/radar/sircxsar/weddell.html

Terrestrial Linear Dune Examples

http://www.jpl.nasa.gov/radar/sircxsar/namibia2.html

http://www.jpl.nasa.gov/radar/sircxsar/egypt.html

Note how similar the Weddell Sea images are to the cat scratches that look like record grooves.

Remember, it's not just their appearance that is important here, but also their relationship to other surface units (also don't forget about differences in RADAR wavelengths) and how the regions they are located in appear in the other RADAR modes, radiometry and scatterometry.

Looking at their GC fractions, it is unlikely that anything heavier than C2H4 was heated enough to lift it from the surface. I guess I could argue that it is not there - if there was enough heating to deplete the C2H2 in such a short time, there should be a few heavier mole fractions in the spectra.



Does this mean they have not completed the chromatograph data analysis yet?
There is nothing simple about the surface of Titan.

So these dunes are more likely composed of sand grains, probably derived from impacts, alluvium, wind, as opposed to hydrocarbon particles from the atmosphere?

Could the Cat-Scratches in the western end of the T3 swath (around Xanadu) simply be a result of hydrocarbon particles from the atmosphere blowing across the surface and gathering in lower areas between hills, where enough accumulates to form dunes?

To help with some kind of comparison, here is the Great Sand Dunes
National Park as seen from space:

http://earthobservatory.nasa.gov/Newsroom/...p3?img_id=17265

A quote from a very recent article in the Christian Science Monitor:

The typical size of sand grains is remarkably constant, whether one looks at Titan, Mars, or Earth, adds Ronald Greeley, a planetary geologist at Arizona State University in Tempe. The grains are roughly the size of granulated sugar. With colleague James Iverson, Dr. Greeley ran lab experiments in the 1980s that suggested Titan's winds might be strong enough to move material around the surface. The new images confirm that work.

“It's great fun to think about one fundamental process operating in such drastically different environments,” he says. The source of Titan's sand remains a puzzle. The team so far has failed to find any obvious ones. One possibility: The supply of sand-like grains have built up over the moon's 4.5 billion-year-history through sunlight-driven chemical reactions in Titan's stratosphere. The resulting particles could have rained to the surface over time. Or, liquid methane flowing on the surface could erode exposed formations of ice “bedrock.”

Where that would occur is unclear, given the absence so far of images of fluids. But images from the European Huygens lander, as well as from Cassini, show features in boulders and the landscape shaped by fluids.

Full article here:

http://www.theithacajournal.com/apps/pbcs....605170304/1024/

Hasso Niemann's "Nature" article: "Heavy hydrocarbons with mole fractions less than 100 p.p.b. may yet be identified in enrichment cell data."



Well, since then we have seen the enrichment cell results (taken in the upper atmosphere) in Dan Harpold's Sept. 2005 presentation to the Harsh-Environment Mass Spectrometry Workshop ( http://cot.marine.usf.edu/hems/workshop/Wo...day/Harpold.pdf , pg. 18), and it very clearly shows hydrocarbons with different numbers of carbon atoms all the way up to an AMU of about 135 -- that is, the maximum range of the mass spectrometer. This meshes very nicely with the results from Cassini's mass spectrometer during its flyby. (We may be looking at polycyclic aromatic hydrocarbons -- that is, clusters of linked benzene rings.)

Footnote: Lab simulations of tholin formation in a nitrogen-methane atmosphere do indeed consistently show large numbers of PAHs.

an AMU of 140 doesn't buy you many benzene rings. would have been nice to look at even larger AMUs. There are obviously some very complex molecules there. It would be cool to find a bucky ball

Why, what would you do with it?

DRIBBLE it.

Also known as coal tars.

Buckyballs are highly unlikely - they do tend to form in oxygen-depleted nitrogen-rich environments, but at very high temperatures.