Splash, schplat, or crunch?

Some thoughts on Ontario Lacus prompted by reading this paper:

It is unique - no other large lakes are observed in the south. It is located far from the center of the south potar regional topographic low. It is unlike the large lakes in the north in that valley systems converging on it do not appear to continue for long distances into the lake in the subsurface topography. Ethane has been detected in it and as the paper points out this is consistent with it having experienced a lot of evaporation to concentrate the ethane. Concentration of ethane implies no major exchange of liquid between the lake and a surrounding alkanofer (anyone got a beter word? - liquifer??). Maybe it's uniqueness is due to it being situated in a uniquely impervious basin.

Lots of questions. What special circumstances could create an unusually impervious basin? Are there any analogues in the northern hemisphere at the present epoch? How might they stand out from the methane-saturated crowd?

Just thinking aloud . . .

Boing? It still might not be strictly speaking a liquid in those lakes- it might be a massive tangle of long chain hydrocarbons with pore spaces that fill up during the wet season and dry out at other times. It could be like a giant rubbery sponge!

EDIT: That wasn't meant in earnest, but this is: What are the odds of the material in ontario lacus haveing non-newtonian properties, like custard? Many polymer solutions do!

Well, Steve Wall has a paper submitted on Ontario with an interpretation of possible wave action on the shores, so
it was probably 'fluid' at some point, and likely is today. In the future it may dry up to the point where the mud
that is left behaves as you described, like, uh, mud, but you actually need quite a high volume fraction of suspended
material to give it non-newtonian behavior like a shear strength.

Now, you don't need that much suspended or dissolved stuff to increase the viscosity somewhat, and in fact
there is a big difference between ethane and methane viscosity. Ethane more viscous, add in a few per cent
of propane, butane and maybe Ontario shouldnt get waves today.

On the other hand, we've only observed Ontario in seasons when winds are predicted not to be high anyway.
Upcoming observations of northern lakes may be different

see (hot onto the presses)
http://www.lpl.arizona.edu/~rlorenz/viscos...es_accepted.pdf

What a fascinating paper! Thanks for posting it here.

Agreed, very interesting paper!

I wonder though, less about waves that might be raised by general circulation winds, or even gravity winds, but what sort of outflow winds the putative Titan thunderstorms might generate. These effects might be dramatic but short lived and so hard to 'catch'.

Has there been any work done on the kinds of effects mesoscale thunderstorm clusters could generate on Titan?

P

Thanks, thats kept my imagination busy for a good while!

That's from the goolaciers calving into the glake.

Gross.

Indeed, if Ontario Lacus is so flat, so smooth, it may be, as you say, because it is made of a viscous material.
I guess that methane, ethane and propane are key elements of this material.

I'm afraid that this viscous liquid or mud has nothing to do, visually speaking, with an atoll on Earth with nice, transparent liquids (unless it is pure ethane or methane).

I keep in mind the enigmatic "Inky Stains" (darker than dark) of Iapetus which may represent the hydrocarbon mud you are imagining.

Link to the image of the Inky Stains:
http://saturn.jpl.nasa.gov/photos/imagedet...fm?imageId=2733

Well, is it possible that *just* the methane moves, and so at the other end of the cycle (which we haven't yet seen) Kraken would be almost entirely ethane?

If I understand it right, there's going to be a complex mix of at least three volatiles in the lakes: nitrogen, methane, and ethane. So the evaporating material would also be an (enriched) mix of the three components, with the more volatile (nitrogen and methane) probably the larger component.

The stuff left behind will be enriched mix in the lower vapor pressure material, ethane in this case.

This is assuming that there is no azeotrope is formed between nitrogen, methane, ethane. ('Course one of the other components in a Titan lake might actually cut an azeotrope, too...)

I don't think it would be possible to have all the ethane left behind in the "pot" and the other components "distilled out".
(Technically an evaporating lake is a single plate distillation of two hydrocarbon solvents (and nitrogen). To be able to get a clean fractional distillation in a lab would require a spinning band distillation with many theoretical plates, again assuming no azeotrope.)

Well it looks like whatever the physical characteristics, the stuff in the lakes exhibit specular reflection ... and rather dramatically.

Glint of Sunlight

Today is the day for dramatic pictures!

Cool, with the exception of the Kraken Mare part

What's wrong with the Kraken Mare part?

The Glint wasn't found in Kraken Mare, but a large lake to the west of it.

Here's a map:

Click to view attachment

Thanks, Jason. Not gonna ask why wrt the error, but do very much appreciate the correction & accuracy!

They sure look connected to me, man. I don't see the problem.

- Jason

Almost connected but not quite. The closest they get to each other is about 95 km between 71.73N,323.43W on Kraken Mare's western shore and 71.68W, 330.36W on the eastern shore of the lake discussed here. These features are far enough south that we have good enough signal/noise to make out the shorelines pretty distinctly.

Not that big of a deal. Just would like to see this fairly large lake (230x70 km) that still doesn't have a name get its day in the sun I would also love to see some of these reflections on Kraken Mare proper. Have to confirm my multi-trillion dollar nestegg after all

That's fantastic - I really wasn't expecting the image itself to be so striking.

Maybe so, but there's no continuous RADAR coverage and I don't see it in the image you posted.

- Jason

They'll just have to call it Kraken-egg Lacus if there's no connection.

Click to view attachmentClick to view attachment

The left image is from T25 (February 2007) and the right one is from Rev88 (October 2008). Both images show Kraken Mare and the lake to the west of it, the originator of the specular reflection according to the location in VIMS's press release. Both show that there is medium-albedo material between the two features, STRONGLY suggesting, based on the appearance of lakes and non-lake solid material in the north polar region in ISS images that there is no connection between the two features. The only hint of one that I can see comes from the T25 image, between the northern ends of both the "sunglint lake" and Kraken Mare, is ruled out in the RADAR SAR data.

That image is stunning and iconic. It speaks to the viewer about liquid on Titan's surface in a way radar images and other remote sensing techniques can't.

Yet another to add to the already superb collection of Cassini images.

Yep! Stunning....... and also - in the best sense of the word - humbling.

Also it's great that people like Jason post here on UMSF so we get interesting and significant corrections (The popular scientific media can be suprisingly sloppy at times). If such a small lake throws such a specular reflection, then ....!!!

+ I got to find out what 'azeotrope' means (Wikipedia saved me !!!).

Oh, so a Titanian lake shows lens flare and everyone loves it... I put a little lens flare on a pic and I'm mentally disturbed...!!!

Love that pic. Outreach gold!

...yeah! From VP's description it ain't all that small, but it sure seems to be smooth. Is there anything to be learned about the presumed light surface winds (little convection, even as the Sun hits it for the first time in a long time?), or the viscosity of the fluid if the surface winds are constrained?

Pretty pic with potentially a great deal of interesting information.

Small....... comparatively!!!

The BBC has a pleasantly unsloppy piece on the proposed Titan Mare Explorer (TiME) Discovery mission, quoting a chap called "Dr Ralph Lorenz". They've used the lake-glint image, which is nice.

I have no doubt that the VIMS folks have done the work to show that this reflection couldn't come from anything but body of liquid methane or ethane, but keep in mind that a specular reflection can be generated by non-liquid surfaces, like the glassy surfaces of basaltic lava flows

Click to view attachment Click to view attachment

Spectacular glint image and I agree with the "iconic" status that Bob Pappalardo gives this image. Now with northern spring we might anticipate seeing more of these coming up. I wonder if the size of the glint is constrained mostly by the size of the lake, size of the sun, or roughness of any waves? Potential glint expansion due to roughness might be more in the "up/down" direction than sideways. Over what range of phase angles will it be possible to observe glints? Looking at the reflectivity of the surface knowing the phase angle could yield the refractive index and thus information about composition.

VP, what type of non-liquid flat material would likely be on Titan? Could we expect basaltic lavas? What is the chance they would correlate in location with the purported lakes on Titan?

Here's another look at T25, Kraken & Sunglint and a higher-res map from VP's N polar map he posted in T48-49 (post #9).

Click to view attachment

I knew it would happen - the moment someone expresses the price of a mission as multiples or fractions of something, someone steps in with an entirely irrelevant movie reference, and someone steps in with a manned v unmanned reference.

Three posts deleted.

"During T64 the RADAR team will be looking for surface changes within the north polar seas Punga Mare and Ligeia Mare during a ride-along observation at closest approach. These seas were also last seen two years ago. Since then, changes in the weather patterns both in the tropospheric methane clouds and higher altitude ethane clouds may have produced changes in the shoreline of these two large lakes. The T64 RADAR SAR swath will stretch from near the north pole south across Titan's anti-Saturn hemisphere down to just north of a bright region known as Adiri."

Looking ahead - Rev123 Dec 18'09 - Jan 03'10

Although you wouldn't expect basaltic flows on Titan, if there is cryovolcanism, then there should be ice flows. What will the surfaces of those flows look like?

Not that I'm suggesting that's what's going on at the north pole. We know what the topography looks like up there -- dissected plains, dark "lakes." This latest result just shows those "lakes" are smooth at a wavelength of 5 microns, which means they're really really smooth.

Jason Barnes, if you're reading this, I'm wondering if you can explain how the public-release image was produced. THe caption only mentioned one wavelength, 5 microns. Is this a colorized image from a single wavelength, or is it produced from more different bands, do you know?

My guess on the ice floes or lava is that it would be a bit more diffuse and thus less intense than what we see for Titan, like in Emily's article showing Antarctica.

For fun and comparison here is a sun glint from Lake Erie:

http://upload.wikimedia.org/wikipedia/comm...ie_sunglint.JPG

Is there a possibility for Cassini to get a shot like this? The solar altitude in the above image may be ~10-15 degrees, seemingly similar to the Cassini shot. Viewing conditions for Cassini might improve as the solar declination increases, over a relatively lower latitude lake. What would the maximum possible solar altitude be over such a lake, maybe 40 degrees? This might be less given the duration of the Cassini mission.

Maybe my main question should be can a similar image be taken at closer range to Titan?

We are well aware that you don't require liquid to have a specular reflection. Clean ice would have one, for instance. But the INTENSITY of the specular reflection of any solid just can't compare to that of a liquid surface. Jason Soderblom is writing a paper detailing the science behind the total intensity of the reflection and its implications for index of refraction of the material, the radius of Titan, size of the sun, distance between them, angle of incidence, and other factors. I'll post it here when it's out, since I'm a coauthor. But it will be a few months -- this is actually pretty hairy when you really get down to it . . .



Right; it is colorized from one wavelength. Actually it is our 16 VIMS channels from 4.8-5.2 microns coadded together and then colorized to a pleasing Titanian shade of orange. I have IR color versions of the image that I've made, but I have to say that I'm not convinced that they necessarily add anything over the one that you see here. Remind me once the paper comes out and I can post them, if you like -- but until then you're stuck with the public image release, I'm afraid!

- Jason

Thanks for the explanation! I'm happy to wait for the paper -- I was just wondering if the color was actually providing any information other than "this is supposed to be Titan"

--Emily

I'll also be looking forward to Jason(s) et al's upcoming paper. Considering some of the factors of reflectance we can look at the Fresnel equations. As an example glass at normal incidence has about a 4% reflection. We can calculate the somewhat lower values for water, and similarly for methane (slightly less than for water) and ethane. This reflectance increases for grazing incidence as can be noticed by looking at the reflection of the sky in a lake at various angles.

Steve

Unfortunately I think this particular image is going to be more iconic than useful, in that the image does
not resolve the structure of the glint (i.e. you don't see the sun's image, or a pattern of speckles
about where the sun image would be - you just see a big square pixel that contains the integrated light
from the pattern). It is a good proof of concept, though, and is prompting the VIMS team to get
their analytical tools together for future opportunities.

The Cassini radio science team also does 'bistatic scattering' experiments, which are essentially the same
thing (but shine radio light from Cassini, observe on Earth). So far they havent published anything on
these experiments over low-latitude surfaces, but some are planned over northern lakes in the
proposed solstice mission.

On the radar team we'd actually considered whether we might see radio sunglint some years ago
(actually an occasional problem for terrestrial orbiting radiometers) - Bartolo Ventura in Bari, Italy
did a good part of his PhD thesis on it. But as for this particular VIMS observation, the spatial resolution
of the real-aperture radiometer doesnt usually allow you to resolve the glint pattern.

On the subject of non-liquid surfaces that can glint, I am reminded of my own commentary in 2003
on the groundbased radar work of Campbell et al which showed striking specular reflections -
see http://www.lpl.arizona.edu/~rlorenz and scroll down to 'Glitter of Distant Seas' for free
link to the Science article. At the time everyone** interpreted these to suggest liquids, but we now
know that the low latitudes on Titan don't seem to have persistent liquids. The question came up
at the time, of course, whether nonliquid surfaces could provide the specular reflections observed.

The answer was that such surfaces would have to be 'flat as parking lots' and they were 20km or
more across, which seemed improbable given what I knew about icy satellite surfaces at the time.
My guess now - and I am now a bit better field-educated on how some real-world sedimentary
surfaces can be that flat, see e.g. Australia and Tunisia pictures also on web page above - would
be that these were flat interdunes (which may well have been liquid-covered in the past)


**including me. No shame in that - simplest explanation at the time. Now we know better - Titan
isnt simple, all the liquids are now at high latitude.

Very informative and interesting, Ralph, thanks!

Just out of curiosity, is the monsoonal model for filling the polar lakes still the working hypothesis? Seems like there's an awful lot of seasonal fluid transfer going on, and it's a bit mystifying to me where all the energy to run the cycle is coming from given the opacity of Titan's atmosphere to so many bands.

All I can think of is that the upper atmosphere must be actively involved in energy absorption & re-emission somehow, but no obvious mechanism jumps out.

Interesting summary and to hear that the VIMS team is considering future opportunities. I wonder if we might be able to speculate on the specular reflection opportunities with a tool like Celestia? Celestia I believe supports specular reflections so one could in theory watch when they materialize using an updated map.

Just curious about the actual location of the glint based on data in the Photojournal image PIA 12481. http://photojournal.jpl.nasa.gov/catalog/PIA12481 The coordinates given are 71deg N and 337deg W. Using VPs north polar map again and using some protractor and caliper based interpolation puts the glint (just barely) in the southern part (referenced to 340W longitude) of sun-glint lake. This lake was also featured in Photojournal image PIA01942. http://photojournal.jpl.nasa.gov/catalog/PIA01942 The lake is notable for its association with many channels (probable inflowing rivers) and possibly is a bit larger than when imaged in Oct. 2006 (about 260 km in length then). The next Titan flyby T64 http://ciclops.org/view/6082/Rev123 probably will not get SAR imaging to see if shoreline changes have occurred. This might be anticipated as the poleward end of the lake appears shallow, showing channel structure within the lake outline.
Click to view attachment

Umm 'still the working hypothesis' ? That hasnt been my view for a year or two - my take is
that the clouds (and rain) are at the poles because of the insolation and circulation (and
maybe it helps that the lakes are there). It is net accumulation (precipitation minus
evaporation) that allows lakes to persist - and I think the precipitation part of the equation
is less important than the evaporation. (The clouds and the lakes may be there for the
same underlying reasons, but the clouds don't cause the seas in the short-term sense, except
for the small transient features noted by Hayes et al and Turtle et al )

You are right, the energetics (my canonical (Science, 2000; even hints in Icarus 1996)
energetic limit of 1cm per earth year on a long-term planetwide average I think still stands,
however rapid (m per earth year) evaporation can locally be on a temporary basis.

Even if you could have 1m per year, my empirical relation for lake volume (GRL, 2008)
of horizontal dimension in km equals depth in m, says Kraken and Ligeia are hundreds of
meters deep, so the present north-south asymmetry in lake distribution must reflect
>centuries and cannot be due to seasonal transfer (hence the longer-term cycle
advocated in the Aharonson article.)

There may be seasonal changes we can observe in these seas (it may be harder to
detect in the northern seas if their margins are steep - the very shallow slopes around
Ontario make the level drop easier to detect as a shoreline migration) but the seas
did not form in a season.

Thanks for the re-baselining, Ralph!

So...interesting implications. The dry lakes in the South might be worthy targets for investigation someday; presumably they hold sediments (chemically modified?) from runoff from higher surrounding terrain. Is there evidence at all for post-evap aeolian deposition on the lakebeds?

Hey, man; I thought that you'd agreed to wait until the detailed papers come out before complaining any more. You've changed your mind, evidently.

Yes, the specular view is unresolved. But we have amazing information about the structure of the glint anyway! Let me try to spell it out so that it makes sense.

By your criterion, signal not spatially resolved, transits of extrasolar planets are useless. The planet is not spatially resolved in any sense, all we have from transits is a big fat pixel, resolved in TIME, that results in a lightcurve. But the lightcurves are spectacularly useful in revealing information about the spatial structure of the planet -- oblateness, ring systems, winds, orbital inclination, orbital eccentricity . . .

The specular glint is useful in precisely the same way. Because the glint is resolved in TIME, and has a whopping signal, forward-modeling with a chi-squared minimization can pull out much of the same information that you could get from a single, spatially resolved observation.

So I would recommend that you revert to your previous policy of waiting for the paper before $#!+ting all over every non-RADAR discovery by knee-jerk.

- Jason

Can you point me at more information which lies behind this empirical relationship - and can any relationship, presumably based on Earth examples, be valid for Titan?

Andy

More iconic than useful..


No offense intended - it wasn't a complaint. Merely an observation that I think this picture is iconic: the
thoughts it provokes are not themselves detailed in the image.
Nor was the remark meant to impugn lightcurve measurements in general.



Not at all. Well, first, we don't have radar images of extrasolar planets as we do of Titan, so the
incremental knowledge from a lightcurve of an exoplanet is dramatic ;-). Second, unless my understanding
of the problem has fallen far behind the state of the art since I cross-examined you during your PhD
defense some years ago, even your ingenious modeling would be hard-pressed to unambiguously yield
the insights you list from a lightcurve of 4 data points (which is what this Titan observation is). Maybe future VIMS
lightcurves will be like those from Kepler and we'll be able to extract all that you hope for, but a lightcurve
plot is not as iconic as this image even though such a plot may actually tell us more about
Titan than this pretty crescent - that's what I was getting at.


It isn't a discovery. It's a confirmation (the image release - which is what prompted the discussion - even says that).