[X] My Assistant

[elakdawalla]

Jonathan Lunine just gave a presentation in a press conference at DPS in Cambridge where he argued that "Titan is perhaps the most Earthlike place in the solar system in terms of the balance of physical processes modifying its surface." He mentioned channels, windblown features, possible lakes, evidence of tectonism, highlands and lowlands. Then he showed a pair of very interesting graphs, which he kindly gave to me, demonstrating how Titan sits in a very Earth-like "Sweet Spot" in the solar system.

The first graph has a plot of mass (normalized to Earth) on the y axis and distance from the Sun (in AU) on the X axis, and contains Venus, Earth, and Mars:



Lunine said that Venus is too close to the Sun so too hot for liquids; Mars is cool enough for liquids but its mass is too low to sustain widespread geologic activity over geologic time scales. So Venus has endogenous volcanism but little evidence of surface modification by liquids; Mars has lots of surface modification, little present endogenous geologic activity. Earth is balanced in between....and so, onto his next graph, is Titan.

Next he shows this graph. Note the axes have changed slightly to mass normalized to Titan and log of distance from the Sun, and he puts on Ganymede, Titan, and Triton, and voila, they map out the same space as Venus, Earth, and Mars on the previous graph:



He argues that Titan sits in an Earth-like "Sweet Spot" and that that's why it's so interesting. Ganymede (and similar Callisto) are like "baked Titans" and Triton (and similar Pluto) is too small for intrinsic geologic activity.

This may be a cartoon with lots of exceptions but I thought it was interesting. But I thought it would be more interesting to plot as many bodies as we can think of on one graph, and draw on distances from the Sun at which you'd expect to see interesting liquids, and see what patterns we can find. (Note someone asked Lunine where Europa would fall, and he said that there are lots of exceptions in the outer solar system because tidal heating messes up the solar distance-surface temperature relationship.) I don't have time to do this though and was wondering if anyone else wanted to have a go at playing with patterns in the solar system.

Emily

[Jyril]

Cool graphs, really interesting. If Ganymede only had a thick atmosphere and volcanism the comparison could have been perfect.

BTW, thanks for the blog entries about the DPS meeting. I was hoping that somebody would tell what results they're revealing there.

[JRehling]

This may be a cartoon with lots of exceptions but I thought it was interesting.  But I thought it would be more interesting to plot as many bodies as we can think of on one graph, and draw on distances from the Sun at which you'd expect to see interesting liquids, and see what patterns we can find.  (Note someone asked Lunine where Europa would fall, and he said that there are lots of exceptions in the outer solar system because tidal heating messes up the solar distance-surface temperature relationship.)  I don't have time to do this though and was wondering if anyone else wanted to have a go at playing with patterns in the solar system.

Emily

Exceptions are just an indication that we need to back up, take a broader perspective and have a new "go" at it!

I would sooner think of the sweet spots in terms of atmosphere/liquisphere: which common compounds or compound pairs are in the right phase/phase transition. Earth is primarily a place where nitrogen is a gas and H2O is a liquid capable of freezing and evaporating. Titan is primarily a place where nitrogen is a gas and CH4 is a liquid capable of freezing (maybe?!) and evaporating. Each has a significant runner-up, too: O2 on Earth (in the gas role) and C2H6 on Titan (in the liquid role).

If you look at solar abundances of volatiles, escape velocities and temperatures (molecular velocity) for all the worlds of the solar system, you get a pretty good prediction of which bodies will have an atmosphere and what it will be made of. The biggest additional considerations are chemical (taking Earth's CO2 out of the picture). So I would say the raw "input" dimensions for a more complete, but still-simple plot of worlds would be: tidal "situation" (zero for most worlds, but significant for Io, Europa, and a few others), radius, and solar distance. From these, atmospheric and crustal temperatures can be deduced; from these, which elements "hung around" in the crust and atmosphere; from these, density and therefore escape velocity; from that, a second iteration at which elements hung around. And that plot would show where respective sweet spots for nice-atmosphere and nice-subsurface are, which probably comes down to where liquid is, though in the interests of thermal chauvinism (chaudinism?), we'll dismiss anything too hot as "magma".

So I only added one dimension to the graph (for tidal heating). Someone with 3D graphics savvy could have at it -- or we could just have two 2D charts and put the tidally-heated worlds on their own chart (in which escape velocity doesn't matter so much).

[Jyril]

BBC News article

Earth and Saturn's moon Titan show striking similarities because both occupy "sweet spots" in our Solar System, researchers have said.

[The Messenger]

Aside from being vaguely corny (akin the the harmonies of the planets) there is a big missing tooth: No ammonia. So what Lunine has constructed is a relationship that struck a strong enough cord to be echoed in the general press, but one that is not based upon observational facts. In other word, Lunine is perpetuating an unsupported myth.

This is annoying, because there are enigmatic factual data emerging from Titan that are all but incomprehensable. This is a great puzzle, but don't expect 'sweet spot' analogies based in part on wishful thinking to help resolve it: Use the data and the chemicals we see, not what has been predicted or imagined.

No one can, at present, explain how the stratified equatorial atmosphere observe from Cassini could produce the vertical shear rates necessary to explain the Doppler patterns observed during Huygens descent.

That's the big story.

[JRehling]

Aside from being vaguely corny (akin the the harmonies of the planets) there is a big missing tooth: No ammonia.  So what Lunine has constructed is a relationship that struck a strong enough cord to be echoed in the general press, but one that is not based upon observational facts. In other word, Lunine is perpetuating an unsupported myth.

I'm not sure what you're talking about here. Ammonia has an interesting role in that it lower the melting point of H2O ice seriously, and so changes the subsurface geology of an icy world greatly when it is present. Is this the One Big Thing you are talking about?

Moreover, this doesn't mean that Lunine's model is not based upon observational facts. It most certainly is. It is incomplete (no one could disagree), but it is based upon facts.

This is annoying, because there are enigmatic factual data emerging from Titan that are all but incomprehensable. This is a great puzzle, but don't expect 'sweet spot' analogies based in part on wishful thinking to help resolve it: Use the data and the chemicals we see, not what has been predicted or imagined.

No one would expect Lunine's model here to explain the intricacies of Titan's unsolved mysteries. I'm sure he's not claiming that, and I don't know why you argue against that. He's just saying that worlds in the right temperature range to have a liquifer have interesting dynamics. It's a trite observation but unquestionably correct.

No one can, at present, explain how the stratified equatorial atmosphere observe from Cassini could produce the vertical shear rates necessary to explain the Doppler patterns observed during Huygens descent.

That's the big story.

I see how ammonia is an interesting part of the picture, and I see (with greater doubt) that Titan's upper atmosphere has dynamics we don't understand. I don't see in the slightest why we should suspect that those things are (other than in a very indirect way) related.

I think you've exaggerated Lunine's purpose and then used that to make vaguely conspiratorial-sounding claims that ascribe to him some kind of malevolence (perpetuating a myth?!?!) that certainly isn't there. Secondly, you seem so eager to elevate the importance of two different phenomena unmentioned in Lunine's model that you call one "the big story" and the other the "big missing" aspect in this modest account he's given, and the overall effect is that you are at best imprecise and unclear and at worst inaccurate.

[elakdawalla]

Aside from being vaguely corny (akin the the harmonies of the planets) there is a big missing tooth: No ammonia.  So what Lunine has constructed is a relationship that struck a strong enough cord to be echoed in the general press, but one that is not based upon observational facts. In other word, Lunine is perpetuating an unsupported myth.

This is annoying, because there are enigmatic factual data emerging from Titan that are all but incomprehensable. This is a great puzzle, but don't expect 'sweet spot' analogies based in part on wishful thinking to help resolve it: Use the data and the chemicals we see, not what has been predicted or imagined.

No one can, at present, explain how the stratified equatorial atmosphere observe from Cassini could produce the vertical shear rates necessary to explain the Doppler patterns observed during Huygens descent.

Messenger,

As Lunine himself said to us at DPS, "The surface of Titan is evidently very complex. Nobody can claim to be able to explain it all." The cartoon he showed was nothing more than a framework on which to base an argument for why Titan is likely to be complex -- not how. Undeniably Titan has held onto its volatiles like nitrogen and methane in an atmosphere whereas Ganymede and Callisto did not, and just as undeniably its surface has been modified in the geologically recent past. Therefore it is complex, and that's all he was saying with his cartoons.

Lunine did argue later that he still thinks that ammonia-water volcanism is the best candidate for what's going on there, based on a variety of data from Cassini-Huygens (e.g. evidence for flows of high-viscosity fluids flowing on Titan's surface, outgassing and retention of volatiles from inside Titan, and isotopic evidence that suggests that Titan's primordial atmosphere must have contained ammonia gas and not molecular nitrogen.) However, as you correctly note, no one has yet seen ammonia on Titan today, which is a puzzle. The point of Lunine's arguments for ammonia-water volcanism are not for him to state that he has the right answer and anyone who disagrees is wrong. The point is that it serves as the best theory he has to explain what he observes on Titan, despite some problems and despite its certain lack of completeness.

As a theory, the idea that ammonia-water volcanism has occurred can be used to generate predictions for what else they may see on Titan. He and the other Cassini-Huygens scientists can then delve into their data and test their predictions. If the predictions more often turn out to be correct than not, they may be on to some part of the explanation for what's going on on Titan. But undoubtedly ammonia-water volcanism can't explain everything, because Titan is a very complex place. Any one theory they have won't explain everything they see, so it will certainly fail to explain the observations in at least some of the cases. Your challenge, as a person who evidently has an opposing point of view from Lunine's, is not to say "his theory is wrong" but to state a theory that you believe explains the observed facts better. Go for it -- show us your theory! What could do a better job of explaining the observed flow-like features on Titan, and the isotopic evidence and composition of the atmosphere?

Emily

[exoplanet]

[quote=elakdawalla,Sep 11 2005, 10:44 PM]


"Lunine did argue later that he still thinks that ammonia-water volcanism is the best candidate for what's going on there, based on a variety of data from Cassini-Huygens (e.g. evidence for flows of high-viscosity fluids flowing on Titan's surface, outgassing and retention of volatiles from inside Titan, and isotopic evidence that suggests that Titan's primordial atmosphere must have contained ammonia gas and not molecular nitrogen.)"

So where is all the ammonia? I suspect that on the surface of Titan the ammonia/water might be reacting to the complex hydrocarbon particles raining down and creating amino acids. Does anyone know if amino acids were detected on the surface by Huygens?

[Guest_BruceMoomaw_*]

Word is that they haven't been identified yet -- although cyanogen, CO2 and a fair amount of ethane have definitely been found among the evaporated surface compounds -- but there are still apparently some more complex organics that haven't yet been firmly named (among the aerosols, too). I rather doubt that Huygens could detect amino acids in any case, though -- they're just not volatile enough to be vaporized by that heated GCMS inlet in Titan's very low temperatures.

I continue to think that ESA screwed up badly by not replacing most of those Surface Science Package sensors (which turned out to be useless anyway) with a heated core tube fastened to the penetrometer shaft and leading to the GCMS. Had they done so, we would now know vastly more about Titan's surface composition at almost no added cost. (In fact, as of the early 1990s, this was apparently the plan. Did the British lead ESA astray in this matter?)

[djellison]

I'm bringing this particular line of discussion to a close.

Messenger - I've asked you in private to keep out of the conspiracy junk, and you're not done it. So I'm asking again in public.

I've has to delete lots of posts in this thread - so we can get it back on track.

I've recieved multiple complaints about this, and I totally agree with their sentiment. Consider yourself warned. That's twice now - and regulars here will know, that's twice more than the norm.

I apologise to those other than Messenger who's posts I've culled, but they just look a bit silly without Messenger's posts between them



Doug