Atmospheric Chemistry of Titan Options

[Juramike]

Here is a "Benzene-O-Vision" graphic showing the amount of benzene and phenyl radicals at high altitudes on Titan. This is based on detections of benzene and phenyl radical (which recombined in the sample chamber to make benzene) using the INMS instrument during closest approach. The numbers are normalized to constant pressure altitude, roughly 1000 km.



The data was taken from Table 1 in: Vuitton et al, Journal of Geophysical Research 113 (2008) E05007. "Formation and distribution of benzene on Titan". doi: 10.1029/2007JE002997 [EDIT 5/24/10: Article freely available here] and overlaid on a map of Titan.

The authors mentioned that the errors in these measurements are 20%.

These detections are well above the detached haze layer. Most are at the same sun azimuth angle. (T23 observation had the lowest angle.) Assuming that the temporal difference is minimal (each dot is from a different flyby), there doesn't appear to be an obvious correlation with latitude.

This graphic does show that benzene is present even waaaay up in the thermosphere and ionosphere.

[Juramike]

I’ve tried to represent Titan’s chemistry in a slightly different way than is normally presented in the literature, the graphic below shows only the key intermediates that react with each other to form major hydrocarbon components in Titan’s atmosphere. Only the dominant pathway is shown for each molecule, so this is a more limited view than the typical “splat diagrams” (example splat diagram in post 27 this thread) shown for Titan chemistry:



On the left side of the matrix are key reactive species. Along the top are some “target” compounds and reactive intermediates. At the cross point are the species formed when these two meet. Note that some of the new species then go back up into the top row or left column. (Everything starts with nitrogen or methane).

In red on the left side is the highly reactive intermediate .:CH radical carbene. This is formed from the electronic recombination of CH3+, which itself was formed from N2 radical cation reacting with methane (the N2 radical cation formed from photoionization of nitrogen using EUV light.) All the compounds formed downstream from .:CH are also boxed in red. Note that almost all the unsaturated intermediates propagate from this compound. As stated before, if there was no CH3+, these couldn’t be formed, so atmospheres with large H2 components (like Jupiter and Saturn) would shunt away from the CH3+ pathways, and only the unboxed (boring saturated aliphatic) compounds would be formed. Think of the boxed compounds as Titan special menu items. This graphic may be valid on exoplanet atmospheres as well, boxed compounds show only those components that could exist where H2 (or other CH3+ absorbing) are significantly absent and allow CH3+ to frag itself up on recombination.