[X] My Assistant

[Guest_BruceMoomaw_*]

http://www.planetary.org/blog/article/00000495/ :

(1) "Ralph Lorenz gave a talk about the dunes on Titan. Since much of the material from his talk is in a paper that is apparently in press in Science, it was a little better developed than I'd heard before. For example, in the past I have heard Ralph cite examples of dune-forms developed in snow in Antarctica where the dunes have almost no topographic expression but are visible to imaging techniques that are sensitive to ice grain size. Now, however, Ralph was reporting measurements of the heights of the Titan dunes -- they average 150 meters high, with a 2-kilometer spacing from crest to crest. He's now citing examples from the Namib desert. He showed some really beautiful Space Shuttle photography of those features."

Lorenz also says -- in both his LPSC abstract ( http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1249.pdf ) and his similar EGU abstract ( http://www.cosis.net/abstracts/EGU06/09468/EGU06-J-09468.pdf ) -- that longitudinal dunes only occur in places where the wind speed fluctuates a lot, which says very interesting things about Titan's weather.

(2) "Guiseppe Mitri presented an interesting modeling study where he asked the question: Are the observations of atmospheric methane relative humidity and thunderstorms/cloud frequency consistent with a desert planet containing tiny fractional lake coverage? According to his calculations, he said, a 50% relative humidity of methane in Titan's atmosphere could result from lakes covering only a small fraction, 0.2 to 4 percent, of the surface. (This was assuming 'tropospheric overturning scales of 10 to 100 years' but I don't know what that means.) I also noted that his calculations implied that if such lakes exist, they evaporate at a rate of 3 to 10 meters of elevation per year."

Mitri added ( http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1962.pdf ) that "The rapid shoreline changes predicted here suggest that repeat Cassini observations of putative lake-like features should be performed at intervals of a year or more: any shoreline changes would provide evidence that candidate lakelike features are actually lakes." The prime target, presumably, should be Ontario Lacus. (I imagine that "tropospheric overturning scales" refer to the average time between a methane molecule evaporating from surface liquid into the air, and its raining back again to the surface as liquid. The longer that time is, the more you can combine high atmospheric humidity with a small amount of liquid actually on the surface. Titan looks more and more like an eerie cryogenic parody of the American Southwest, where its "sands" and its rare but violent rainstorms are concerned -- but its reasons for that storm pattern are somewhat different.)

[Guest_BruceMoomaw_*]

The "Science" report on the latest interpretation of the GCMS findings said that there were some indications of more complex hydrocarbons, but those results are still being analyzed. There certainly seems to be something of the sort when you look at the actual GCMS spectra -- but keep in mind that the heavier such hydrocarbons are, the harder it would have been for the warmth of the heated vent on the instrument (which wasn't touching the surface) and the warmth of Huygens itself to vaporize them out of the soil to where the GCMS could reach them.

The fact that the instrument DID definitely seem to detect significant quantities of vaporized cyanogen and benzene fascnates me. Neither of those compounds has any kind of low vaporization temperature. According to Wikipedia, cyanogen melts at -28 deg C and boils at -20 deg C, while benzene doesn't melt until +5.5 deg C and doesn't boil until fully +80 deg C! If the GCMS really was picking up whiffs of these, there must be one hell of a high concentration of them on Titan's surface -- far more than was expected. (Some CO2 was picked up, too -- suggesting a pretty high concentration of that too, since its sublimation point, although a lot lower than that of the above compounds, is still far higher than Titan's surface temperature.) By contrast, theories predicted a lot of frozen acetylene and HCN (which both vaporize at low temperatures) accumulated on Titan's surface -- but there seems to be no firm confirmation yet of HCN, and there's no evidence for lots of acetylene (although the team's abstract for the upcoming EGU meeting mentions in passing that it was detected. Except for that, there's nothing new in that abstract.)

So there may be some quite surprising and complex organic reactions taking place on the surface, AFTER the original smog particles (consisting mostly of ethane, acetylene and HCN, according to theory) land there. Given the extremely slow rate at which all these compounds accumulate on Titan's surface (only 100 meters or so each of acetylene and HCN over all the eons of Titan's existence), is it possible that Titan's cryovolcanism has recycled virtually all of them downward through the crust and into the zone of liquid water or water/ammonia, causing quite complex reactions to occur before the products are spat back up to the surface? (Benzene is supposed to be one of the commonest polymers of acetylene.) Yet again, I regret like hell the fact that Huygens didn't carry a heated core tube hooked up to its GCMS, rather than most of those [naughty word] British surface sensors.