[X] My Assistant

[Steffen]

Which device made the Huygens probe spin underneath its satellite?
I read that's the way how 360° images were made during descent...

[Guest_BruceMoomaw_*]

That same diagram revealed something else that I hadn't paid proper attention to: the heated inlet for the GCMS is squarely in the center of the probe's slightly convex bottom -- which, given that Huygens did land in fairly soft mud (albeit with pebbles in it) makes it highly likely that the inlet (heated to fully 80 deg C) DID come into direct contact with Titan's surface material. Indeed, Raulin and Owen's 2002 "Space Science Reviews" piece ( http://www.nasa-ksc.org/outgoing/SSR/raulin.pdf ) says: "The GC-MS has a heated inlet tube that extends several mm beyond the probe’s outer skin. A landing in a fluffy drift of aerosols would therefore provide access to an unusually concentrated sample of the organic compounds that the atmosphere of Titan has produced during many hundreds of millions of years. Even a successful touchdown on water ice could provide useful information."

And Hasso Niemann's piece in the same issue ( http://www-personal.umich.edu/~atreya/Arti...romatograph.pdf ) says: "If the Probe settles into a deposit of aerosols, one needs to extrapolate the accumulated information from the descent measurements to interpret the data. This would offer an opportunity to determine the level of chemical complexity achieved by chemical synthesis in the atmosphere, as even rare aerosols may accumulate inmeasurable concentrations on the surface. Here the GCMS heated inlet will ensure that the more volatile components of such aerosols reach the instrument. Landing on exposed ice could still permit a measurement of H2O ice ‘bedrock’ and a search for condensed CO2, measurements of fundamental importance to an understanding of atmospheric evolution. A determination of D/H in H2O on the surface would be of great interest for comparison with atmospheric values in CH4 and other species. It is recognized, however, that this is the most challenging landing scenario, both for Probe survival and for a good interface between the gas inlet and the surface...

"The most probable landing position is expected to be upright, which is also optimum for the instrument. In case of a landing on a liquid surface, the heated inlet tube will be submerged in the liquid, which will rapidly evaporate in the inlet tube and the vapors will flow through the inlet lines."

OK. So the odds actually look pretty good that that very hot GCMS inlet tube did come into actual contact with Titan's surface, or at any rate came so close that it very dramatically heated the surface. What are the implications? Well, this makes it easier to explain how the GCMS detected benzene on the surface, despite the latter's very high boiling point (80 deg C, exactly the same temperature as the inlet). On the other hand, it makes it more interesting that Huygens apparently detected relatively modest amounts of other substances with tremendously lower boiling points which were expected to exist there in quite large amounts: methane, ethane, acetylene. (Even solid HCN -- which theory predicted to have accumulated there in fairly large amounts -- has a boiling point of only 26 deg C; but apparently they still haven't confirmed beyond doubt that Huygens detected it on the surface at all. And while Huygens did detect a fair amount of cyanogen there, its boiling point is only -20 deg C.)

So -- if I'm interpreting the raw graphs of the GCMS data at all correctly ( http://www.nature.com/nature/journal/v438/...ature04122.html , Figure 1) -- the amounts of low-temperature volatiles on Titan's surface were much more modest than expected, but there was quite a bit of benzene there. Now, I'm not even remotely sure that I AM interpreting those GCMS graphs correctly -- if anyone out there knows more about the behavior of mass spectrometers than I do, I wish you'd take a look at them and report your own conclusions. Nevertheless, this is interesting -- especially since benzene is supposed to be one of the commonest polymers of acetylene, which was expected to exist in quite large amounts on the surface as frozen solid powder. Once again, I wonder if Titan's cryovolcanic activity isn't causing it to circulate the smog that lands at an incredibly slow rate on its surface down into Titan's interior, allowing those compounds to be exposed to the liquid water (or water/ammonia) down there and chemically modified before they are spat back up onto the surface. (In the "Nature" graphs, note all those intriguing little peaks over on the rightward part of the GCMS graphs implying the detection of some much heavier compounds on the surface.)

And, oh yeah, I can't resist annoying Alex further by reporting that while I was poking around in Google just now to find all this, I also stumbled across the fact that Prof. Erik Asphaug had reprinted my own lengthy description here of the ESA's post-landing Huygens press conference in toto to his grad students on his Solar System blog ( http://marsseminar.blogspot.com/ , Jan. 21 entry). So there: OTHER scientists appreciate me properly, Alex. Boy, will you be sorry some day you didn't treat me right. It almost makes up for that little three-orders-of-magnitude mistake I've just discovered that I made in calculating Enceladus' ice loss rate... (It also kind of makes up for the fact that during my own sojourn at UCSC three decades earlier, the only class I took remotely related to planetary science was an introductory geology course in which I got an extremely lousy grade.)