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Posted by: BruceMoomaw Mar 2 2005, 12:36 PM

..or, Move Over, Muad'dib. I've finally, belatedly, gotten around to reading his 2002 book "Lifting Titan's Veil", and was amazed at how many of Huygens' discoveries he foresaw in advance. To wit:

On pg. 79, he says: "The idea of enough nitrogen being caught directly in the ices that went into Titan is not plausible because it is such a volatile substance. Ammonia conversion seems to be the most plausible way for Titan to acquire a nitrogen atmosphere."

On pg. 100, he predicts that the discovery of argon-40 in Titan's atmosphere would mean that the argon produced by the decay of K-40 in Titan's interior has found a way out, "vented through cracks or spewed out by volcanoes" -- and that this would provide still further evidence that Titan's methane is being released the same way from clathrates trapped inside Titan during its initial formation, especially if we also discover that Titan's nitrogen is isotopically fractionated but that its methane is not. Bingo. (Of course, as he points out, the ESA's ISO satellite had already discovered solid evidence that Titan's nitrogen is fractionated even before Cassini got there and confirmed this -- with most of that nitrogen fractionation probably having occurred during the strong T-Tauri solar wind period of the early Solar System, before much of Titan's methane had been released from its interior.)

On pg. 108, he notes that -- while Titan simply does not receive enough solar energy to evaporate more than 5 cm of liquid methane off its surface yearly, which limits its maximum possible total yearly rainfall to that of a terrestrial desert -- this still leaves the possibility of sudden, powerful local cloudbursts and flash floods, again of the sort characteristic of Earth's deserts. "The sheer amount of methane in the dense Titan troposphere implies that a single event could dump a meter of rainfall. While most rivers on Titan may be dry, river valleys may yet be abundant and deep."

On pg. 115, he mentions some recent research noting that -- while methane rainfall by itself would have trouble dissolving enough of the complex dark organic goo that's accumulated on Titan's surface to wash its higher areas clean -- Patrice Coll's experiments had shown that liquid methane mixed with small amounts of the nitriles that form in Titan's air is far more effective at doing so. "In effect the nitriles are acting as a soap, dissolving the otherwise insoluble materials, just as real soap dssolves fats that are insoluble in water" -- and allowing high-altitude methane rainfall to produce the otherwise inexplicable light color of Xanadu and Titan's other highland regions. (Methane frost is unworkable as an explanation for this because the highlands would have to be unaceptably high for CH4 frost to form on them, especially considering the strong antifreeze effect of nitrogen mixed with that methane.)

On pg. 154, he notes that the erosive power of occasional flash floods of liquid methane across the surface is likely to be further enhanced by the fact that Titan's surface temperature is near the boiling point of methane, encouraging the formation of local brief pockets of cavitation as it flows. And liquid methane is already somewhat likely to have more erosive power than water to begin with, because of its lower viscosity and thus its stronger turbulence. "If rivers carry much debris, either eroded ice particles in suspension or organic sludge, they may perhaps form large deltas where they empty into lakes. We'll see."

On pg. 226, he describes his habit of amusing himself on his frequent flights between Europe and the US by looking out at the various types of landscapes he sees out the window and speculating which one will best match Titan's surface. "I am sometimes rewarded by clipping the southern tip of Greeland. Is Titan like that rolling expanse of pristine white down there, calving into icebergs? Probably not. Maybe more like the smooth, nearly bare rock of NE Canada, sloping gently into sea...Or maybe Titan looks more like the desert of the southwest USA I see on frequent trips between Tucson and JPL -- flat expanses of sediment between mountains, with the occasional canyon, dried-up lake bed and dune field. Perhaps it's all of the above. Titan is a wide world too..."

And on pg. 200, talking about his experiences helping to manage Cassini/Huygens: "A particular frustrating experience has been the over-vigorous application of ITAR in the USA particular following the case of [Web Ho Lee]. Many aerospace components like accelerometers and, perversely, even the software used to predict Cassini's trajectory through space and its orientation, are classified as 'munitions' and their access by non-US nationals is restricted... These kinds of problem work both ways, however. [The Doppler] error in the Huygens radio system design might have been picked up before launch and corrected if critical details were not stuck in an Italian factory to which JPL experts did not have easy access." Now, of course, the ESA is blaming ITAR for the failure to pick up the software error that led to the loss of Huygens Channel A.

He did foul up on a couple of predictions: he didn't foresee the extreme shortage of craters on Titan, and on pg. 127 he remarks on the extent to which Titan may have wind gusts that might make the probe "swing under its parachute...Certainly the atmosphere should be less blustery than on Earth, but beyond that we simply don't have enough information to make a robust estimate." As things turned out, of course, its stratosphere had gusts violent enough to almost turn the probe over. Fortunately, its radio link -- even at Cassini's longer than planned distance -- was solid enough that no data was lost due to misaiming of the antenna during these moments.

A few other interesting notes from the book:

(1) He remarks on how incredibly lucky we were to get the 1989 occultation by Titan of the naked-eye star 28 Sagittarii -- and, on top of that, the unexpected flash when the star was directly behind Titan, caused by its light being refracted completely around the moon: "Although occultations by Titan of such a bright star would be expected once every 50,000 years, seeing such a central flash would be expected only once every million years!"

(2) He provides a description of just how clearly we'd be likely to see Saturn from Titan's surface -- namely, not very: "Saturn itself to human eyes would be at best barely visible at night -- aa bright fuzzy patch in the sky, like a full Moon all but hiden by cloud on Earth. If we could see at slightly longer wavelengths, it would be spectacular, however: Saturn would be essentially as bright as a full moon on Earth but would be 12 times larger..."

(3) I'd completely forgotten that, during the selection of the Cassini/Huygens instruments in 1990, they came close to adding the flight spare of the Galileo probe's nephelometer to Huygens before deciding that DISR would do an adequate job by itself of profiling Titan's cloud and haze layers in detail. In retrospect, this may have been a mistake.

(4) He explains the reason for the slight last-minute rescheduling of Cassini's third and last targeted Enceladus flyby in March 2008 -- namely that, while the initial flyby designers had checked to make sure the target region would be on Enceladus' dayside, no one had thought to check whether Enceladus would be in Saturn's shadow at that time, which it turned out to be starting just a few minutes before the flyby.

(5) Last but not least, we get his brief and embarrassed explanation of the infamous Condorman Affair: "A TV company making a documentary about the moons of the solar system called me to ask about Titan and I let slip the business about flying. Me and my big mouth. I'd also let slip the porpoising idea [in which it's harder to simply swim on Titan than on Earth because of the human body's negative buoyancy in liquid methane, but one can easily build up enough speed to leap completely out of the 'water' porpoise-style in its weak gravity],and the next thing I knew I was swimming in Mono Lake at 6 AM in the buoyant but unpleasantly alkaline waters. Later that day I had a pair of wings strapped to my back. Hopefully these antics may inspire someone to think that Titan is an interesting place. At least I got a free pair of flippers and a ride in a hot air balloon out of the deal."

Posted by: Bill Harris Mar 2 2005, 02:54 PM

Thanks for the review. Cambridge University Press, also available from Amazon.com and other fine booksellers.

Mine is on order...

--Bill

Posted by: MiniTES Mar 2 2005, 04:06 PM

Yes- that was an excellent book. I read it two years ago and have been using it as a reference to understand the importance of the various Cassini/Huygens discoveries (e.g. the methane flash floods idea, argon-40, ammonia becoming the nitrogen atmopshere, other things alluded to by Bruce). Absolutely essential for understanding Titan - it is the amateur astronomer-level reference for Titan (and by that I mean above the level of Scientific American but somewhat below the level, of, say, Icarus).

Posted by: volcanopele Mar 2 2005, 04:59 PM

A definite recommend... and I'm not just saying because Ralph is in my office..or at least his voice is...

Posted by: imran Mar 2 2005, 05:06 PM

I have always admired Lorenz's work on Titan. Although I have not had a chance to read the book yet, I am not surprised to hear that he was right on many accounts. The only reason I never purchased the book was because I convinced myself that I could wait another two years for Cassini's arrival at Saturn.

Posted by: The Messenger Sep 13 2005, 07:08 PM

I have perhaps made a bigger deal out of this than I should have, but the complete lack of detectable ammonia - by either Cassini or Huygens - seems to put a kabosh on this mechanism, at least for now.

IAOTO a reducing atmosphere should contain a GCMS-measurable airbourne fraction if there are significant quanties of ammonia in-solution on Titan's surface. The Ammonia IR peak is also very broad and discernable.

Bruce has verified that it has not been detected, but just how sensitive are the instruments, and why wouldn't Cassini and/or Huygens detect it?

Lunine is still presenting models that require copious amounts of ammonia, after all but announcing ammonia is a major player on Titan in February.

http://www.universetoday.com/am/publish/ammonia_key_titan.html?2122005

Saying so does not make it so. How much should a model lacking a key element be touted?

Posted by: BruceMoomaw Sep 13 2005, 11:32 PM

No, it doesn't necessarily -- because NH3 breaks down VERY fast (tremendously faster than CH4) on exposure to solar UV, of which a sizable amount hits Titan's surface dspite its dense atmosphere. (For the same reason, I'm very skeptical that the failure of Cassini to detect NH3 in Enceladus' surface ice means that large amounts don't exist in its subsurfce ice.) We are seeing some indications that a lot more outer Solar System N2 than expected exists originally as HCN rather than as NH3, though. It may be time for me to do some quizzing of the relevant scientists.

Posted by: The Messenger Sep 14 2005, 01:07 AM

Thanks Bruce. While I was in college, I worked in a lab, and ran ammonia tests in the ppm level with a specific ion electrode. If anyone, anywhere on the floor (including the janitor) opened a bottle of ammonia, it screwed up my tests.

I have also run experiments on the solar breakdown of azide compounds. It took a lot longer than we expected at this solar distance, and we were working with bright sunshine on clear days.

Ammonia is more volatile than water, so if we are observing water vapor above Enceladus, we should also be observing ammonia. I don't think it is there.

Posted by: JRehling Sep 14 2005, 01:15 AM

NH3 is not only not a gas at Titan's temperatures -- it is a solid. You don't see a lot of magma in the Earth's atmosphere...

NH3's only chance to be in Titan's atmosphere would be as dust.

Posted by: The Messenger Sep 14 2005, 05:02 AM

So is water, but we still find water vapor in the air, especially around the vents of Enceladus. Both water and ammonia will have a vapor pressure, a solubility in nitrogen gas that is very, very low on Titan and Enceladus, but not zero.

The melting point of NH3 is 195k and the vapor pressure @ 195 K is 45kg/m^2, and that is at one atmosphere. If there is a water/ammonia slurry on the surface, in significant quantities, we should also find ammonia in the atmosphere.

Posted by: JRehling Sep 14 2005, 05:57 AM

Enceladus is quite a different situation from Titan, so let's address that separately.

Have we found H2O in Titan's atmosphere? Mass spectrometers couldn't tell H2O or NH3 from heavier-isotope versions of CH4, so I'm not sure why you say "we still find water vapor in the air." Note that if you find the absence of NH3 to be an anomaly, the two gas spectrometers that have had a go at Titan can not be used to speak to this matter either way.



195 K is not relevant. What is the vapor pressure of NH3 at 94K? It is literally off the chart here...

http://www.airliquide.com/en/business/products/gases/gasdata/images/VaporPressureGraph/Ammonia_Vapor_Pressure.GIF

Extrapolating from that, it's certainly very very low. What makes you say it would be detectible?

Posted by: BruceMoomaw Sep 14 2005, 09:35 AM

"Ammonia is more volatile than water, so if we are observing water vapor above Enceladus, we should also be observing ammonia. I don't think it is there."

Again, not necessarily -- NH3 also breaks down under solar UV vastly faster than water does. But, again, I will have to make enquiries.