[X] My Assistant

[jsheff]

Have you seen these stunning descent images from Huygens?

Huygens views

[Guest_BruceMoomaw_*]

I would now be very hesitant to say that we didn't pick up any traces of water or ammonia evaporated from the surface. We could identify benzene very easily because of its particular AMU (78), which had no other compounds with similar AMUs to confuse the results -- but, when you look more carefully at Niemann's graph, the actual amount of the stuff that Huygens detected evaporated out of the surface was very tiny. The same is true for cyanogen (52 daltons). By contrast, water and ammonia both have AMUs very close to the very strong, dominating 16-dalton peak for methane -- and acetylene and HCN similarly have peaks very close to the even stronger 28-dalton nitrogen peak.

So it may have been seriously premature for me to say what I was saying earlier -- namely, that really freakish amounts of cyanogen and benzene were found on the surface while there were shortages of the other expected compounds. It may well just be that those expected compounds really do exist in much bigger amounts on Titan's surface, but were simply concealed from clear GCMS detection by Titan's CH4 and N2. I still haven't talked to Niemann himself on this.

Meanwhile, some French lab simulations have -- if I remember correctly -- found that tholins containing nitrogen tend to be orange, while those just consisting of hydrocarbons tend to be black. I'll track this abstract down.

Thanks for this very useful picture. Just one thing about the height of rain formation - my impression of the white clouds seen earlier was that they were pretty tall affairs, even compared with the large scale height of Titan's atmosphere. Richard suggested a plausible convection mechanism arising from the lower density of methane-rich air. Unlike the case of thermal convection a rising column of intrinsically less dense air would not simply cool and equalise its density with the surroundings but presumably go on rising until most of the methane had condensed out. As condensation nuclei are scarce, especially lower down, I imagined this happening quite high up, perhaps directly to the solid state as snow or hail which would then melt on the way down. Am I completely wrong about this? (If so a one word answer will suffice!)

I doubt that this effect is any more important for Titan than for Earth. We're talking about just a few percent of methane in Titan's air (and just a few percent of water vapor in Earth's air), and the density difference between that gas and the dominant gases in the air is similar for both worlds. In both cases, I think we're simply dealing with a wet-adiabat phenomenon -- that is, humid air rises until it's reached a cool enough level that its condensable gas (CH4 or H2O) condenses into liquid, releasing a fresh burst of stored heat energy that rewarms the air to loft it still higher. But this phenomenon must be less dramatic for Titan than for Earth simply because water releases much more heat energy when it condenses than methane does. And Titan's clouds are still very low in its overall atmosphere (about 12 km, I believe).

J, although you don't actually know it, there is a deckchair and a rolled up newspaper just out of shot in the huygens surface image....

I remember predicting in 1969 that the first thing Neil Armstrong would see on the Moon would be a beer can.