Could someone point me at a reference for the currently accepted atmospheric composition for Saturn? Thanks

Gary

This paper:

http://ej.iop.org/links/q56/UEWmd2+HfAdcyQ...rpv53i6p793.pdf

Cites [Gautier 88] with an estimate (with unimpressive uncertainty) of 6% He by mass (H2 would be about everything else). That translates to 97% H2 and 3% He by volume.

The same estimate is given here:

http://arjournals.annualreviews.org/doi/pd...1.050183.002215
(p. 17 of the file)

You'd think there'd be a Cassini estimate, but I haven't seen it.

CIRS saturn results

Not very much on Saturn in this one...some people are working on it, but no papers yet. Also, lots of gound-based observing of Saturn going on.

A good pre-Cassini summary (also Titan atmospheric composition) can be found here (Table III, pp.195 for the Saturn composition):

CIRS preview

JRehling,

Thank you. The first URL was dead. It doesn't follow that there is no Cassini based estimate for Saturn's atmospheric composition. There would have been numerous opportunities for radio occultation data to provide such an estimate. I'll have to do a proper literature search. Thanks again.

Gary

Radio occultation gives no direct composition information. It provides information on refraction and attenuation by ray paths through an atmosphere as a function of height. The refraction is inverted mathematically to yield an estimate of density with height. Assuming hydrostatic equilibrium, they convert that to temperature profiles.

Adiabatic convection, which yields nearly constant Delta-Temp with altitude, tells you directly the scale height of the atmosphere and depends on the gas' mean molecular weight. That tells you hydrogen/helium proportion, approximately, but that's about it.

Breaks in adiabatic convection may be linked to the bases of moist convecting clouds (wet vs dry adiabat is a term here) and if you know what the cloud's condensing gas is, you can determine the amount of that gas in the atmosphere at the height where condensation starts.

What is the reference for the currently accepted atmosphere density / temperature versus altitude for Saturn?

It might be my memory playing tricks on me but I vaguely remember seeing a graph of radio signal amplitutde versus frequency for a Voyager carrier beam through Titan's atmosphere. That information was used to determine species concentrations in Titan's atmosphere based upon dropouts at certain frequencies due to specific species absorption. Again, I could be all wet about this. Also a radio technique that worked for hydrocarbons might not work for hydrogen / helium.

My interest in Saturn's atmosphere comes from some preliminary conversation about doing a Saturn probe. People are saying that another Jupiter probe like Galileo won't be near term due to the Juno orbiter (a mistake IMHO). A Saturn atmospheric probe is easier to do than a Jupiter probe like Galileo due to Saturn's shallower gravity well. Also, people are interested in going back to the Saturn system because of Titan and of course, because Saturn is genuinely interesting. The argument follows that a Saturn probe proposal might actually be funded (not holding my breath). We have flight data from the Galileo probe. The main source of heating during the Galileo Probe's entry into Jupiter's atmosphere was thermal radiation from the hot gas behind the shockwave (shocklayer). The intensity of shocklayer thermal radiation is strongly a function of helium molar concentration. If we designed a Saturnian atmospheric probe's heat shield based upon the Galileo Probe then the Saturn probe might be over designed (too much heat shield mass) because Saturn has less helium in its atmosphere. Again this is all conversation and probably nothing will come from it. However I need to start educating myself about Saturn just in case they tell me to do design work in support of a Saturn probe proposal.

Posts from "stupid isn't it" thread on Saturn's atmospheric composition moved here.

...and add a little propane

"The first detection of propane on Saturn

Thomas K. Greathouse, , John H. Lacy, Bruno Bézard, Julianne I. Moses, Matthew J. Richterd and Claudia Knezb"

Icarus V.181 pp.266

As I noted on another thread, the giant-planet science community has now firmly decided that the next mission after Juno to specifically study a giant planet should be a Saturn flyby that would drop off 1 to 3 entry probes which would share Galileo's vented and lightweight design, since it's now thought that just analyzing the atmosphere down to 20 bars will be adequate for the outer three giant planets for a while -- provided that the main craft also uses a microwave spectrometer like Juno's to measure the water and ammonia at greater depths. This would be a New Frontiers-class mission -- maybe even solar-powered -- and there's a good chance that a proposal of this sort will be submitted at the next New Frontiers AO. (It might, alternatively, be a similar flyby of Uranus or Neptune, again with relatively shallow entry probes -- but in that case the main craft would carry more instruments and must be RTG-powered.)

A new CHARM presentation is out.

The topic is Saturn Atmospheric Results from Cassini/VIMS.

http://saturn.jpl.nasa.gov/multimedia/prod...M_Baines_FC.pdf

(Watch out, it's an 18-meg pdf!)

Normally, I don't pay too much attention to CHARMs, but this is an interesting presentation. Thanks for the heads-up, Bart.