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Unmanned Spaceflight.com _ Titan _ Titan's changing lakes
Posted by: ngunn Jan 29 2009, 07:22 PM
Today's big news?
http://ciclops.org/view/5471/CASSINI_FINDS_HYROCARBON_RAINS_MAY_FILL_TITAN_LAKES
Changes in the south polar region were announced late last year. Is there more to this story now??
Posted by: ngunn Jan 29 2009, 07:32 PM
Aah, there's this:
http://saturn.jpl.nasa.gov/multimedia/images/moons/images/PIA11146-th120.jpg
and this:
http://saturn.jpl.nasa.gov/multimedia/images/moons/images/PIA11147-th120.jpg
Posted by: volcanopele Jan 29 2009, 07:34 PM
Here are some the associated graphics:
http://photojournal.jpl.nasa.gov/catalog/PIA11147
This shows the changes that we are highlighting in this paper. Basically, between July 2004 and June 2005, a 31,000 sq. km area of the south polar region of Titan went from being nondescript to being a patchwork of dark features. These darkening is thought to result from the deposition of liquid methane and dark sediment in this area. The mostly likely mechanism for this change is that a major rainstorm in the 11 months between the observations rained out, filling a low-land region, a playa, within a shallow layer of liquid methane.
The most likely storm to cause this was a huge storm system seen from the ground and by ISS in early October 2004. Based on ISS observations, the most intense part of the storm (as determined by the brightest part of the storm which likely represents the area with the greatest cloud heights) on October 8, 2004 was directly over this region.
http://photojournal.jpl.nasa.gov/catalog/PIA11146
This is the labeled version of my August 2008 map. Of particular interest in this map is the polar coverage we are now achieving. In the north polar region, we see a field of dark spots on the leading hemisphere and several large methane seas (Kraken Mare, Ligeia Mare, and Punga Mare). These features were previously seen by RADAR and likely represent lakes. The number of dark features seen in the south polar region exceed those seen by RADAR in its swaths of the region, suggesting that some have dried up since 2005.
Posted by: volcanopele Jan 29 2009, 07:35 PM
QUOTE (ngunn @ Jan 29 2009, 12:22 PM)
Changes in the south polar region were announced late last year. Is there more to this story now??
The paper was published on GRL website and was "in press" starting in early December. This press release is going in conjunction with that paper actually being published in the print version of the journal.
Posted by: ngunn Jan 29 2009, 07:45 PM
That's brilliant, thanks VP.
Posted by: Jason W Barnes Jan 29 2009, 09:11 PM
I actually much prefer that these press releases coincide with actual scientific papers; it increases the signal-to-noise. Any damned idiot can put out a press release, but without a peer-reviewed paper to back it up it's just gum-flapping. This is the first time that this discovery has been announced. You here of the cognescenti know of it from Dr. Turtle's DPS talk, but this is the first public release.
The ISS team did this one right, and by the book, so don't give them crap for it!
- VIMS Jason
Posted by: ngunn Jan 30 2009, 02:14 AM
QUOTE (Jason W Barnes @ Jan 29 2009, 09:11 PM)
The ISS team did this one right, and by the book, so don't give them crap for it!
No-one's doing that - certainly not me. I'm 100 percent delighted with what they (and all the other instrument teams) do. The images and map associated with that release are new to me. If they were posted here before, I missed them. Until now I didn't know exactly where the newly 'flooded playa' was, and I found the comments in the article most interesting.
Not so long ago there were people here (not the mission scientists) saying that Titan doesn't receive enough solar energy to empty and fill the lakes on a seasonal basis. I'm hoping 2009 brings us more, and that this is just the beginning of Cassini's record of Titan's surface changing with the seasons.
While you're on the line - can you shed any more light on the question of using the ISS polarisers to look for sky reflections in the lakes? There probably are reasons why it isn't worth trying but I can't discover them.
Posted by: Jason W Barnes Jan 30 2009, 05:33 PM
QUOTE (ngunn @ Jan 29 2009, 08:14 PM)
While you're on the line - can you shed any more light on the question of using the ISS polarisers to look for sky reflections in the lakes? There probably are reasons why it isn't worth trying but I can't discover them.
Well, since the lakes are at the poles the incidence angle is always going to be 70 degrees or higher. Therefore to see a specular reflection, you'll need to look with emission angle of 70 degrees or higher as well. As you know from processing the ISS data, the empirical atmospheric correction that they do does not produce reliable surface photometry this close to the limb. Look at Mezzoramia in the Turtle et al. paper -- the brightness looks quite different between these two flybys, when there's every reason to think that it hasn't actually changed at all.
Another reason is that you'd need a very specialized encounter geometry in order to be in position to see the specular reflection. I can't speak for ISS. But as for VIMS, we've made the decision that if we were in such a geometry, we'd rather be looking straight down at the ground with 0 emission angle, as that would mean new territory at fine resolution.
This type of observation may have been rendered moot by the T49 RADAR altimetry pass -- we'll have to wait until that's been released to find out. Hope this helps,
- VIMS Jason
Posted by: ngunn Jan 30 2009, 08:16 PM
That is indeed most helpful. Although I'm still not clear why the direction of the sun should be a constraint if one is only looking for a reflection of the hazy sky, I can well appreciate how the other difficulties might mount up.
What is the RADAR turning up I wonder? Like many others I await that too with eager anticipation.
Patience is needed there I know, but the upcoming flyby will provide plenty of excitement in near-ish real time. Seatbelts fastened, a quick wave at the lake and in we go!
Posted by: Decepticon Feb 2 2009, 10:57 AM
Does anyone have a radar swath overlay-ed of the south pole?
Have lost mine and have been unable to locate it.
Posted by: titanicrivers Feb 2 2009, 03:15 PM
QUOTE (Decepticon @ Feb 2 2009, 04:57 AM)
Does anyone have a radar swath overlay-ed of the south pole?
Have lost mine and have been unable to locate it.
Check post # 29 http://www.unmannedspaceflight.com/index.php?showtopic=4835&view=findpost&p=107096 by Olvegg in the T39 flyby topic; a portion of that SAR included the S Pole. Hmm... looks like those new lakes are present on the background image in that post (but not necessarily in the swath path).
In the animation below the S. Polar terrain is shown before and after the October 2004 storms along with the approximate location of the T39 SAR swath.
Posted by: rlorenz Feb 4 2009, 03:36 PM
QUOTE (ngunn @ Jan 30 2009, 03:16 PM)
What is the RADAR turning up I wonder? Like many others I await that too with eager anticipation.
Patience is needed there I know
LPSC abstracts will be out soon - there will be something for you there
Posted by: ngunn Feb 4 2009, 09:11 PM
Excellent!!
Posted by: nprev Feb 5 2009, 12:37 AM
Oh, goodygoodygoody...Santa Ralph hints that a bit of Christmas is coming early this year!
Posted by: Juramike Feb 7 2009, 04:48 PM
Bam! There it is!
Lorenz et al. LPSC (2009) Abstract 1990 "ONTARIO LACUS : BRILLIANT OBSERVATIONS OF A TITAN LAKE BY THE CASSINI RADAR
ALTIMETER."
Available here: http://www.lpi.usra.edu/meetings/lpsc2009/pdf/1990.pdf
Ontario Lacus is flat, and deep, no bottom echo by RADAR.
Posted by: ngunn Feb 7 2009, 07:20 PM
Brilliant discovery - brilliant paper title!
I'm not so sure that we can deduce anything much about the depth. The shoreline gradient is very small, yet even for the (one would think) shallows near the shore no bottom reflection is detected, presumably because the direct reflection from the surface is just so much brighter. I note that "T60 will provide another . . opportunity where the observation can be tuned better" - maybe to look specifically for a bottom echo?? And before that there is the T58 SAR. How much will it resemble the northern lakes?
Exciting stuff.
Oh - I almost forgot there's a few other abstracts to look at as well !!!
Posted by: ngunn Feb 8 2009, 08:37 AM
Taking this together with earlier VIMS results, may we tentatively conclude that the ISS- and SAR- areas hitherto coloured blue on published images actually comprise significant areas of gently sloping 'mudflat' as well as areas of standing liquid? If so we have to question how much of the large northern lake district is actually liquid-covered. Are the SAR details seen inside the inferred shorelines mudlats, lake bed features, or a mixture of the two? Will it require altimetry to find out? What are the implications for the proposed lake boat?
Posted by: rlorenz Feb 9 2009, 06:22 PM
QUOTE (ngunn @ Feb 7 2009, 02:20 PM)
Brilliant discovery - brilliant paper title!
But apparently not perceived as such by the program committee - I got postered.
Apparently the tired old story of salts on Europa and some other reruns were
considered more worthy of oral presentation... :-{
Posted by: nprev Feb 9 2009, 07:57 PM
Hmm. Sorry to hear that, Ralph; it was indeed a great paper!
I wonder sometimes if the community as a whole is kind of intimidated by Titan in some ways. It's SO different that interpreting even basic surface features is a significant challenge.
Posted by: ngunn Feb 9 2009, 09:15 PM
Or perhaps other 'disadvantaged' topics were felt to be in need of positive discrimination?
Anyhow, for us distant abstract-consumers one format is much like another and each new revelation is a treasure.
Perhaps Ralph will take a question from the floor here. It's about surface gravity waves on the lake. I would like to ask whether this observation, or others like it, can be used to place limits on either the height or gradient of surface waves. For example can we say from this that the surface (in the brightest part) is smooth and flat right down to centimetre scales?
Or is there still the possibility of an oily swell? (sorry)
Posted by: Jason W Barnes Feb 10 2009, 01:52 AM
QUOTE (rlorenz @ Feb 9 2009, 12:22 PM)
But apparently not perceived as such by the program committee - I got postered.
Apparently the tired old story of salts on Europa and some other reruns were
considered more worthy of oral presentation... :-{
WTF? Program committee on crack is what that is.
- Jason
Posted by: rlorenz Feb 15 2009, 04:21 AM
QUOTE (ngunn @ Feb 9 2009, 04:15 PM)
Perhaps Ralph will take a question from the floor here. It's about surface gravity waves on the lake. I would like to ask whether this observation, or others like it, can be used to place limits on either the height or gradient of surface waves. For example can we say from this that the surface (in the brightest part) is smooth and flat right down to centimetre scales?
Or is there still the possibility of an oily swell? (sorry)
Yes, the echo shape and amplitude (and the radiometry) pose severe constraints on how flat the lake
surface must be - a detailed modeling effort is ongoing.
Posted by: ngunn Feb 15 2009, 07:51 PM
Great - another potentially variable lake property accessible for occasional monitoring by Cassini. I look forward to the first results.
Posted by: Jason W Barnes Apr 10 2009, 11:32 PM
VIMS Ontario Lacus paper is now out in print from either Icarus ( http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4V9S471-4&_user=854313&_coverDate=05%2F31%2F2009&_rdoc=18&_fmt=high&_orig=browse&_srch=doc-info(%23toc%236821%232009%23997989998%231037085%23FLA%23display%23Volume)&_cdi=6821&_sort=d&_docanchor=&_ct=30&_acct=C000046079&_version=1&_urlVersion=0&_userid=854313&md5=2d3d76722006651b3b490613a43ebb98 )
or from my website ( http://www.barnesos.net/publications/papers/2009.5.Icarus.Barnes.Ontario.Lacus.Shoreline.pdf ). We only have one look, so no direct evidence of changes, but the bathtub rings certainly imply lake level changes over time, anyway .
- VIMS Jason
Posted by: ngunn Apr 11 2009, 07:26 AM
A huge thank you (again) for making another fascinating paper available to all. I haven't had time to digest it fully, but noticing this concluding sentence
Knowledge of the amplitude of the changes will require reliable topographic
information over Ontario Lacus with both high precision
and fine spatial resolution — the T49 RADAR altimetry pass, should
it occur, will shed light on these processes.
reminded me that we already have a link to that altimetry profile in post 15 of this thread.
Posted by: titanicrivers Apr 11 2009, 12:28 PM
As above. A very readable and yet compelling paper with great figures and a nice discussion. Appreciate the work and especially the free link posted here, Jason.
Posted by: ngunn Apr 11 2009, 10:04 PM
Is anybody going to have a go at matching the altimetry to the VIMS map of the lake's southeastern margin? Did the altimeter track pass over those red islands in the VIMS interpretation diagram?
A nice feature of the VIMS is the clear boundary between unit 1, interpreted as standing liquid, and unit 2, interpreted as possible mudflat. The distinction seems to be less marked in radar SAR images of the northern lakes, presumably because the liquid is just too transparent to microwaves and it's surface virtually invisible (unless you're looking straight down in altimetry mode at the specular reflection of the transmitter).
Posted by: Jason W Barnes Apr 12 2009, 06:25 PM
QUOTE (ngunn @ Apr 11 2009, 03:04 PM)
Is anybody going to have a go at matching the altimetry to the VIMS map of the lake's southeastern margin? Did the altimeter track pass over those red islands in the VIMS interpretation diagram?
A nice feature of the VIMS is the clear boundary between unit 1, interpreted as standing liquid, and unit 2, interpreted as possible mudflat. The distinction seems to be less marked in radar SAR images of the northern lakes, presumably because the liquid is just too transparent to microwaves and it's surface virtually invisible (unless you're looking straight down in altimetry mode at the specular reflection of the transmitter).
I saw a profile across it somewhere -- which probably means that Ralph showed it to me. So hopefully he'll put an explicit comparison in an upcoming Ontario Lacus altimetry paper.
- Jason
Posted by: HughFromAlice Aug 23 2009, 06:08 AM
The variation in the height of the surface of Ontario Lacus has been constrained to within a range of a few millimetres.
There is an abstract (you will have to pay for the full research paper) pubished in Geophysical Research Letters on Aug19 on the - Smoothness of Titan's Ontario Lacus: Constraints from Cassini RADAR specular reflection data. Available at http://www.agu.org/pubs/crossref/2009/2009GL039588.shtml It has recieved good publicity in the popular scientific press, such as http://www.newscientist.com/article/dn17665-saturn-moons-mirrorsmooth-lake-good-for-skipping-rocks.html
As an amateur who is fascinated by Titan - and in particular its lakes and 'methano-ethanological' cycle - I thought that this 19Aug abstract was v interesting. While not proof that Ontario Lacus is filled with liquid, I think that there would be few people who would bet a week's wages on it having any sort of solid surface after reading about how incredibly smooth it is.
It is interesting to see how this research has been built on data from the T49 Dec08 pass. I read a paper a while ago by Ralph (Lorenz - who posts regularly right here) on this pass. Very interesting regarding the specular reflection. http://www.lpi.usra.edu/meetings/lpsc2009/pdf/1990.pdf ....Now team member Lauren Wye (whose speciality is signal detection) has built on this, by working out a way to more accurately analyze the strength of the specular return by partly overcoming distortion factors caused by the flash. This has allowed an upper boundary in height variation of the surface to be set at 3mm.
To me this looks like a brilliant conclusion to the work of a highly multiskilled team! Congratulations. (No pun intended - it is more than a flash in the pan!).
Posted by: Gsnorgathon Aug 23 2009, 05:29 PM
Hey! I got lucky and got the http://www.agu.org/journals/gl/gl0916/2009GL039588/. (Does that make me a criminal?)
Posted by: rlorenz Aug 23 2009, 06:26 PM
QUOTE (HughFromAlice @ Aug 23 2009, 01:08 AM)
To me this looks like a brilliant conclusion to the work of a highly multiskilled team! Congratulations.
It was Lauren who did all the work. One of those discoveries that starts with 'that's odd....'
(namely that the amplitude histogram of the echoes was nonGaussian. Essentially the surface is
so flat that the echo power is dominated by returns from a small area (almost a point target)
and the echoes are sufficiently in phase that the saddle-shaped histogram of the transmitted
chirp is retained.) Thus we can get information showing that few-hundred-meter-wide areas
on Ontario are flat at a fraction of a radar wavelength.)
The effort was complicated by the saturation of the signal, which was then lossy-compressed,
although Lauren managed to reverse-engineer the processing chain to recover some quantitative
backscatter numbers nonetheless.
This experience let us fine-tune the re-observation on T60 with stronger attenuator settings.
Unfortunately that data were lost due to the DSN outage.
So, the elevation profile (reported in my LPSC abstract) shows Ontario is flat to ~10m over
tens of km, and the echo histogram data show it is flat to ~3mm over ~100m scales.
Flat as a millpond, as they say
Posted by: nprev Aug 23 2009, 09:08 PM
It's a fascinating result, Ralph, and clearly some impressive instrumentation detective work was involved. Congratulations to you & your associates!
Of course, this apparent extreme flatness begs a lot of questions. Can the surface winds of Titan really be that torpid over such a substantial surface area? You would think that at least a few ripples would be generated by (presumed) small-scale atmospheric convection due to the temperature differential between the liquid & the surrounding shore, unless the whole system is truly isothermal. Alternatively, could the fluid itself be extremely viscous due to the presence of complex organics/contaminants (like runoff sediments from rainstorms), or do we have an inadequate understanding of the gross physical behavior of low-temp methane/ethane/whatever mixtures?
As usual, major discoveries always produce many more interesting questions. I don't see some of these being resolved until we splash (or plop) a probe into one of these lakes.
Posted by: djellison Aug 24 2009, 08:01 AM
QUOTE (rlorenz @ Aug 23 2009, 07:26 PM)
Flat as a millpond, as they say
Minus the ducks. Their wake would have ruined the 3mm factor
Posted by: AndyG Aug 24 2009, 08:26 AM
Reading this made me think of the artwork by Richard Wilson. It's entitled 20-50 - essentially a room full of old sump oil, perfectly flat, very smelly, of "unknown" depth, and highly reflective at low angles. You can walk into it...
(Picture nabbed from the Saatchi Gallery site)
Posted by: ngunn Sep 1 2009, 11:24 AM
BIG changes observed at Ontario Lacus in the 4th abstract here:
http://www.abstractsonline.com/plan/ViewSession.aspx?sKey=0a85480c-4d97-408f-9551-9adfcf8a8005
Posted by: titanicrivers Sep 1 2009, 12:40 PM
QUOTE (ngunn @ Sep 1 2009, 05:24 AM)
BIG changes observed at Ontario Lacus in the 4th abstract here:
http://www.abstractsonline.com/plan/ViewSession.aspx?sKey=0a85480c-4d97-408f-9551-9adfcf8a8005
Hmm... don't seem to be getting that link to work nigel. Any other link to follow?
Posted by: Hungry4info Sep 1 2009, 01:15 PM
QUOTE (titanicrivers @ Sep 1 2009, 06:40 AM)
Hmm... don't seem to be getting that link to work nigel.
I confirm.
Posted by: ngunn Sep 1 2009, 01:34 PM
Strange, it works for me OK, although it does involve two steps - clicking on the title of the fourth paper in the session.
However, assuming you're not even getting to the Session programme try going the long way round from the link I just posted in 'conferences and publications'. Follow links to 'Titan Surface'.
Lots of other goodies there too.
Posted by: belleraphon1 Sep 1 2009, 01:54 PM
All..
I found I had to outside the forum and go directly to the DPS 41st web page to get these abstracts...
The one in question is in Session 21 Titan surface... I am copying the abstract here because others have had problems getting to this.
Yes, ngunn a lot of juicy abstracts on this site ....
"Title Further Constraints on the Smoothness of Ontario Lacus using Cassini RADAR Specular Reflection Data
Author Block Lauren Wye1, H. A. Zebker1, R. D. Lorenz2, J. I. Lunine3, Cassini RADAR Team
1Stanford Univ., 2Johns Hopkins University, Applied Physics Lab, 3University of Arizona, Lunar and Planetary Lab.
Abstract Cassini RADAR altimetry data collected on the 49th flyby of Titan (T49; 2008 December 21) over Ontario Lacus in Titan’s south polar region shows evidence for intense mirror-like specular reflections. Analysis of the strength of the specular return, which is expected to decline exponentially with increasing surface height variance, reveals that the surface is extremely smooth, with less than 3 mm rms surface height variation over the 100m-wide Fresnel zone (“Smoothness of Titan’s Ontario Lacus: Constraints from Cassini RADAR specular reflection data”, GRL 2009). The T49 echoes were stronger than expected, severely saturating the receiver and inhibiting an accurate estimation of the signal strength and, consequently, the rms surface height. While we developed a method to partially correct the echoes for the distortion incurred, our height estimate is only an upper limit. Further altimetry data over Ontario Lacus is expected in the T60 sequence on August 9th, 2009, where the receiver attenuation will be set high enough over the lake to avoid saturation, and quantization effects will also be minimized. In this presentation, we will report our latest estimates on the smoothness of Ontario Lacus’ surface and what they might suggest for limitations on the wind speeds or surface material characteristics.
This work was conducted under contract with the Cassini Project and was partially supported by NASA headquarters under the NASA Earth and Space Science Fellowship Program. "
Craig
Posted by: belleraphon1 Sep 1 2009, 01:57 PM
And, of course, I copy the wrong abstract... sorry admins...
"Title Evidence for Liquid in Ontario Lacus (Titan) from Cassini-Observed Changes
Author Block Jonathan I. Lunine1, A. Hayes2, O. Aharonson2, G. Mitri3, R. Lorenz4, E. Stofan5, S. Wall3, C. Elachi3, Cassini RADAR Team
1Univ. of Arizona, 2Caltech, 3Jet Propulsion Laboratory, 4Applied Physics Laboratory, 5Proxemy Research.
Abstract The first SAR observations of Ontario Lacus were made by the Cassini RADAR on passes T57 (June 22, 2009) and T58 (July 8, 2009), providing a nearly complete microwave view of a large lake first seen in ISS images (McEwen et al., BAAS 37, 739, 2005.) Subsequent Cassini VIMS observations of Ontario Lacus indicated the presence of liquid ethane in the lake (Brown et al., Nature, 454, 607, 2008). Comparison of the ISS and RADAR images, taken about 4 Earth years apart, seem to show that the extent of the liquid region--interpreted to be the sharp light-dark boundary at each wavelength--has shrunk. Assuming a topographic slope no larger than 0.1% based on altimetry from the T49 pass of adjacent areas, the shrinkage yields a change in the volume of the liquid of about 15 cu.km.-- an upper limit because the RADAR sees more deeply into the lake than does the ISS. We seek to determine the cause of the shrinkage. The seasonal phase of Titan between 2005 and 2009 permits the hypothesis that the evaporation of methane or ethane from the lake has been responsible. The evaporation of methane will be energy-limited thanks to its large vapor pressure at the southern near-polar temperature of about 92 K (Jennings et al., ApJ, 69, L105, 2009). The maximum evaporative flux at the summer pole is roughly 2 W/sq.meter (Mitchell, JGR, 113, E08015, 2008), leading to a loss over the four years between ISS and RADAR observations of about 20 cu.km of liquid methane. A second approach, assuming advective transport of warm and dry air over the lakes, yields a value several times larger. Ontario Lacus has changed in a way consistent with the hypothesis that it is filled with methane/ethane liquid.
This work is supported by the Cassini Project."
Craig
Posted by: remcook Sep 1 2009, 02:36 PM
How well do the ISS and RADAR 'shorelines' correlate for the northern lakes?
Posted by: ngunn Sep 1 2009, 03:09 PM
I have to admit I'm baffled by the numbers right now. Area 20 000 sq.km. and volume change 15 cu.km. imply a height change of just 0.75m. They quote an upper limit of 0.1 percent for the bottom gradient - that would translate to a minimum horizontal shrinkage of only 750 metres, surely unobservable in IR. Perhaps it's a lot wider than that, with even shallower gradients. I think we must wait for the full presentation to find out what's really been observed.
Still 15 cubic kilometres is a lot of liquid - enough to fill Loch Ness twice.
Posted by: Sunspot Sep 1 2009, 03:40 PM
So when will us common folk get to see the T57/T58 SAR RADAR results?
Posted by: titanicrivers Sep 1 2009, 05:20 PM
QUOTE (ngunn @ Sep 1 2009, 07:34 AM)
Strange, it works for me OK, although it does involve two steps - clicking on the title of the fourth paper in the session.
However, assuming you're not even getting to the Session programme try going the long way round from the link I just posted in 'conferences and publications'. Follow links to Surface'.
Lots of other goodies there too.
See if I can get this link to the goodies to work!
(nope, will try another)
http://www.abstractsonline.com/plan/start.aspx?mkey=%7B38381CEF%2D2A25%2D4ED4%2D81F6%2D08CED373A512%7D
That one seems to work.
Posted by: ngunn Sep 1 2009, 06:18 PM
I've edited my previous post 42 to correct a numerical error.
When will we see the SAR? I'd guess around conference time.
Posted by: HughFromAlice Sep 1 2009, 11:30 PM
QUOTE (titanicrivers @ Sep 2 2009, 02:50 AM)
See if I can get this link ....to work!
This one works fine! A treasure trove! 50+ orals on Titan alone! I'd love to see this presentation on Oct 6th........ 21.03 - Further Constraints on the Smoothness of Ontario Lacus using Cassini RADAR Specular Reflection Data. Wye et al.
For anyone wanting an overview - book accom etc. go to http://dps09.naic.edu/ Wish I had the time. Long way to go from here!
Posted by: volcanopele Sep 1 2009, 11:34 PM
Well, hopefully they will broadcast the oral sessions online like they did last year.
Posted by: ngunn Sep 3 2009, 11:12 AM
This presentation will compare apparent shorelines for the whole lake between 2005 and 2009, but also relevant is the partial VIMS view from T38 so perhaps this is a good place to repost the link to that paper:
http://www.barnesos.net/publications/papers/2009.5.Icarus.Barnes.Ontario.Lacus.Shoreline.pdf
For at least part of the shoreline we should have a nicely spaced 3 stage progression - ISS 2005, VIMS 2007 and SAR 2009. It will be particulatly interesting to see how the SAR fits with the detailed interpreations of the shoreline features offered in the VIMS paper.
Posted by: Olvegg Oct 7 2009, 06:11 PM
http://www.spaceref.com/news/viewpr.html?pid=29332
http://www.universetoday.com/2009/10/06/new-evidence-of-seasonal-change-on-titan/
Posted by: ngunn Oct 7 2009, 08:38 PM
Spectacular changes - and so plain to see! (No peering hard at these images to make out what the scientists are talking about.)
Spaceref seems to be suffering from bipolar disorder though, given that the actual title of the CalTech press release was:
'Cassini RADAR Observes Seasonal Change in Titan's South Pole'.
Posted by: ngunn Oct 7 2009, 09:50 PM
I am trying to post the VIMS image of the bottom right end of the lake but spectacularly failing - either to copy or attach it, so this is the best I can do.
Go up to post 48, open the Barnes paper and scroll down to page 5. There I think you will see the islands near the mouth of that river that also appear in the SAR, along with a caption outlining the VIMS team's interpretation of the shoreline features. At first glance the VIMS data and interpretation dovetails fine with the ISS/RADAR story.
Posted by: volcanopele Oct 7 2009, 10:02 PM
I think the ISS/VIMS/RADAR story is coming along nicely. It definitely seems clear that the observed paucity of lakes in the south and the abundance in the north noted by RADAR seems to be due seasonal bias: the north is in its wet season, and thus has more filled lakes, while the south is it its dry season where the lakes generally dry up (temporary fillings due to storms not withstanding, as seen by ISS 2004/2005). By the end of the XXM perhaps we will see the opposite pattern, an abundance of filling lakes in the south, and shrinking lakes in the north. Kraken Mare may slowly become a mudflat, and Mezzoramia "Mare" may become the great southern sea.
Posted by: ngunn Oct 7 2009, 10:28 PM
Link from remcook:
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4WW2SPC-D&_user=10&_coverDate=07%2F28%2F2009&_alid=1025117161&_rdoc=2&_fmt=high&_orig=search&_cdi=6821&_sort=r&_docanchor=&view=c&_ct=9&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=607f9aff1b85003af9c22eeb4cd844bd
The abstract contains the statement that the lakes fill up due to precipitaion in summer and dry out by evaporation in winter. Any comments?
Posted by: volcanopele Oct 7 2009, 11:58 PM
I guess my comment is that I think they have it backwards...
Posted by: titanicrivers Oct 8 2009, 03:32 AM
QUOTE (Olvegg @ Oct 7 2009, 01:11 PM)
http://www.spaceref.com/news/viewpr.html?pid=29332
http://www.universetoday.com/2009/10/06/new-evidence-of-seasonal-change-on-titan/
HA! Check out my post in the SAR 48-49 thread, post # 6 placed on Oct 3rd. I showed the same change in the lakes comparing the T36 and T49 overlap region as is discussed in the second paper in Olvegg's post above! While I thought the change from radar dark to radar bright in the floor of these small pothole lakes or calderas might be a seasonal drying up effect I wasn't really sure. This seems to be the radar teams reasoning as well.
Posted by: Sunspot Oct 8 2009, 07:53 AM
How wide is thay channel where it appears to open out into the lake?
Posted by: Webscientist Oct 8 2009, 08:54 PM
QUOTE (volcanopele @ Oct 8 2009, 12:02 AM)
I think the ISS/VIMS/RADAR story is coming along nicely. It definitely seems clear that the observed paucity of lakes in the south and the abundance in the north noted by RADAR seems to be due seasonal bias: the north is in its wet season, and thus has more filled lakes, while the south is it its dry season where the lakes generally dry up (temporary fillings due to storms not withstanding, as seen by ISS 2004/2005). By the end of the XXM perhaps we will see the opposite pattern, an abundance of filling lakes in the south, and shrinking lakes in the north. Kraken Mare may slowly become a mudflat, and Mezzoramia "Mare" may become the great southern sea.
So, the next probe may not choose the north polar lakes or seas for its landing site!
Indeed, Mezzoramia may become the Kraken Mare of the south polar region.
The Huygens probe may become a wreck in the depth of the potential sea which is likely to take shape as the giant ethane cloud ( currently engulfing the north pole) migrates toward the south.
Posted by: volcanopele Oct 8 2009, 09:03 PM
The landing site might depend on the season when the boat would land yes, but I think what is perhaps most clear is that we need to observe Titan over more of its year before we take even what I said as gospel truth.
As far as the fate of Hugyens, keep in mind that the ethane cloud doesn't literally migrate. As spring progress it will likely just fade in the north and form up in the south rather than actually moving between poles.
Posted by: nprev Oct 8 2009, 09:13 PM
Hmm. It does seem as if the 'desert' equatorial regions get some gully-washer storms, though. Huygens sure looks like it's sitting in a flood channel...maybe an arroyo?
Would expect such storms to start popping as the season change progresses, if they happen with any regularity at all.
Posted by: volcanopele Oct 8 2009, 09:18 PM
Yeah, and storms are not unheard of at the latitude of the Huygens probe, but not that giant ethane cloud at the north pole.
Posted by: nprev Oct 8 2009, 09:36 PM
Gotcha. I'm definitely thinking flash floods are possible in Huygen's neighborhood, but not long-term standing bodies of liquid.
Posted by: ngunn Oct 8 2009, 09:53 PM
QUOTE (nprev @ Oct 8 2009, 10:13 PM)
Huygens sure looks like it's sitting in a flood channel...maybe an arroyo?
It seems ages since I posed the question: Where is Curien Station? Is it for once and all the latitude and longitude where the probe landed, or does it move when Huygens gets washed along a bit, maybe even buried? (The first option is itself problematic as we now know, due to the variable rotation state of Titan's floating crust.)
I think a typical surmise just now would be that at any given tropical location floods are more like millennial events than seasonal ones. The changes now unfolding at high latitudes are exciting enough but, as VP points out, we need to watch for a few years more before anyone can do more than make informed guesses about the big picture. That's what's so great about this amazing active world. Everyone has a ringside seat at the show and
nobody knows what may happen next.
Posted by: Juramike Oct 8 2009, 11:27 PM
QUOTE (ngunn @ Oct 8 2009, 03:38 PM)
Oh well, I had to ask.
Here's my shot at Fig 2b trying to zero near the "Spooky Dude" formation.
From: http://www.lpi.usra.edu/meetings/lpsc2009/pdf/1599.pdf.
Graphic is of Fib 2b masked and infilled with a hue/saturation adjusted and contrast adjusted and Gaussian blurred [0.5 pixels] Fig 2c - Fig 2a (after masking line & text area and underfilling with vortex-modified Karoschka mosaic).
Looking forward to the full article....
[EDIT: Even with this hack job, one can see that the R1, R2, and R3 balance out to the correct colors. So if the Spooky Dude formation is in the VIMS, it could be either R1 (bright region terrain) R2 (blue region) or something else that spectrally resembles either of those. R3 (brown region = dune material) can be safely ruled out.]
Posted by: djellison Oct 9 2009, 04:33 PM
Some posts have been removed from this thread, as they contained links to and images from data that should not yet have been in the public domain.
Posted by: titanicrivers Oct 10 2009, 03:01 PM
Check out Photojournal http://photojournal.jpl.nasa.gov/targetFamily/Saturn from today. Posted are two superb figures that were presented by Alexander G. Hayes at the Division for Planetary Sciences meeting of the American Astronomical Society on Oct. 6, 2009. Olvegg has posted the links to the presentations earlier in this thread (post #49).
Posted by: ngunn Oct 25 2009, 09:48 PM
VIMS sees specular reflection from Kraken Mare:
QUOTE:
After more than 50 close flybys of Titan by the Cassini spacecraft, it has become clear that features similar in morphology to terrestrial lakes and seas exist on Titan’s surface. Widespread evidence for fluvial erosion, presumably driven by precipitation of liquid methane from Titan’s dense atmosphere is also apparent from these data. Lake-like features have thus far only been observed in Titan’s polar regions. Of these presumed lakes, liquids have only been conclusively identified in Ontario Lacus, a relatively small lake in Titan’s south-polar region. As Titan progresses into northern summer, the much larger lake-like features in the north-polar region identified in Radar data, are becoming directly illuminated for the first time since the arrival of Cassini. This allows the Cassini optical instruments to search for specular reflections to confirm the presence of liquids in these presumed lakes. On July 8th, 2009 the Cassini Visual and Infrared Mapping Spectrometer (VIMS) successfully detected a specular reflection in the north-polar region of Titan. The signal is restricted to the VIMS channels at ~5 µm where most of the incident light reaches the surface without being scattered by aerosols in Titan’s atmosphere. By mapping these observations onto the RADAR image from the T19 flyby, the VIMS specular reflection was found to be associated with the western part of Kraken Mare, one of Titan’s large northern lakes, indicating the lakes surface is mirror like, strongly suggesting it is liquid.
(with thanks to 'Gish Bar Times' for the link to these abstracts).
Posted by: ngunn Oct 25 2009, 10:50 PM
And there's so much more - here:
(struggling to post a link that works)
http://agu-fm09.abstractcentral.com/planner.jsp
OK that works. Now: Browse / Friday / Planetary Sciences and you're there.
Posted by: ngunn Oct 26 2009, 12:01 AM
Personal anecdote: perhaps not many people remember their 57th birthday as one of the best. I do. Not only did we have this VIMS observation of northern lakeshine, but also the Ontario SAR:
QUOTE (Sunspot @ Jul 2 2009, 02:27 PM)
Ontario Lacus......... at last
The SAR of Ontario Lacus was long expected and advertised, but the VIMS Kraken Mare specular reflection was not mentioned in the July 8 Mission Description or in the 'Looking Ahead'. I wonder if it also was expected, or purely serendipitous?
Posted by: ngunn Oct 26 2009, 01:34 PM
Another morsel from the conference abstracts. Anything to do with timescales on Titan always grabs my attention. This one was hiding outwith the dedicated Titan sessions. Because of the difficulty of linking to these abstacts I'm going to try posting a series of short QUOTES from:
Geomorphic Analysis of North Polar Channel Networks on Titan, and Implications for Active Tectonics and Persistence of Relief Structures
R. Cartwright1; J. A. Clayton
"Assuming constant 1.5 m depth liquid hydrocarbon flow during the summer (wet) season, we estimated that roughly 19,800 Titan years are required to lower Basin A down to its minimum relief."
"recent tectonic uplift could help explain why this region displays variable relief, as well as contorted and constricted channel networks"
UNQUOTE
If I understand correctly this implies that typically the relief confining Titan's lake basins only formed within the last million (Earth) years or so, or else the basins are continuously deepening themselves at a pace that matches erosional degradation of the topography. The timescale tallies quite well with the ages of terrestrial lakes, relatively few of which go back more that a million years.
Posted by: Jason W Barnes Oct 26 2009, 02:00 PM
QUOTE (ngunn @ Oct 25 2009, 02:48 PM)
On July 8th, 2009 the Cassini Visual and Infrared Mapping Spectrometer (VIMS) successfully detected a specular reflection in the north-polar region of Titan. The signal is restricted to the VIMS channels at ~5 µm where most of the incident light reaches the surface without being scattered by aerosols in Titan’s atmosphere.
Gosh I hadn't realized the word was out yet. I guess if AGU abstracts are published then there's a good reason for the leakage . . .
- Jason
Posted by: ngunn Oct 26 2009, 02:33 PM
Catching the lakeshine:
Radar 21st December '08 - VIMS 8th July '09 - Go ISS!
Posted by: Jason W Barnes Oct 26 2009, 02:46 PM
QUOTE (ngunn @ Oct 26 2009, 07:33 AM)
Catching the lakeshine:
Radar 21st December '08 - VIMS 8th July '09 -
Go ISS! Considering we only saw it at 5um, and not at 2.8, 2, 1.6, 1.3, or 1.1, I think that ISS is going to have a challenge finding it at 0.93um.
- Jason
Posted by: ngunn Oct 26 2009, 03:04 PM
Yeah, you caught the sun's direct reflection at a pretty oblique angle, right? A very spectacular result - I look forward to seeing the crucial image when it's published. I realise the haze makes that impossible for ISS but I'm still hoping (until I'm told otherwise) that they may be able to identify specularly reflected skylight near the Brewster angle.
Posted by: Jason W Barnes Oct 26 2009, 05:32 PM
QUOTE (ngunn @ Oct 25 2009, 05:01 PM)
The SAR of Ontario Lacus was long expected and advertised, but the VIMS Kraken Mare specular reflection was not mentioned in the July 8 Mission Description or in the 'Looking Ahead'. I wonder if it also was expected, or purely serendipitous?
I guess if those are the only two options, then it's "serendipitous". We have been looking for specular reflections all the time, but haven't seen any -- the reason of course is that the Sun hasn't been shining on the wet places (Ontario excepted). So while we look at the images and keep specular in mind, we haven't before designed a sequence around it. Now that we've found one and see how totally cool it is, though, and what great science can be done with it, we're looking for opportunities in the future to do a planned specular campaign. It all depends on the spacecraft geometry, though, so we pretty much just have to wait for the right time.
- Jason
Posted by: ngunn Oct 27 2009, 12:41 PM
Thanks, Jason. Congrats to the team and good luck with future targeted lakeshine studies.
Posted by: rlorenz Nov 1 2009, 03:11 PM
QUOTE (Jason W Barnes @ Oct 26 2009, 01:32 PM)
Now that we've found one and see how totally cool it is, though, and what great science can be done with it, we're looking for opportunities in the future to do a planned specular campaign.
- Jason
As I've remarked to you in person, it is totally cool. But what is the great science ? Since the specular point
is just that at any given instant, the geometry varies with time (i.e. the angle varies as the point tracks across
the surface, so you don't vary angle and position independently [this is also a problem in the radio equivalent -
the bistatic scattering experiment, results of which from T12 years ago have yet to be published] - maybe it's
not too much variation, I guess may depend on the specifics of a given observation.) If you
can resolve the brightness distribution around the specular point, then it is an interesting measure of roughness
across an assumed uniform structure like a lake, although is it any better than a SAR image of the same thing?
But a single pixel specular reflection is of limited utility, I think....
Not to be a (shiny) wet blanket, and I repeat, it is cool, but by itself it isnt telling us a lot about Titan unless I am
mistaken.
Posted by: ngunn Nov 1 2009, 07:25 PM
Excuse a very basic question: would that be one pixel at one wavelength or do you get an IR spectrum for that pixel?
Posted by: Juramike Nov 1 2009, 08:05 PM
QUOTE (ngunn @ Nov 1 2009, 02:25 PM)
Excuse a very basic question: would that be one pixel at one wavelength or do you get an IR spectrum for that pixel?
Each pixel is being observed at the VIMS IR wavelengths. So, in theory, you'd get an IR spectrum for each pixel location. In practice, the methane absorptions limit how many wavelengths you could observe, then atmospheric scattering makes some of those wavelengths (esp. the shorter ones) difficult as well.
Somebody's gonna have fun applying all the atmospheric and haze corrections to get the corrected spectra.
It'll only be close to a "perfect mirror" at a few select wavelengths due to the intervening atmosphere. Kind of fun to imagine a funhouse mirror that would only reflect "blue" and "orange" but nothing else.
Posted by: ngunn Nov 1 2009, 09:17 PM
QUOTE (Juramike @ Nov 1 2009, 08:05 PM)
applying all the atmospheric and haze corrections
I was thinking this kind of observation could be a powerful means of
quantifying those things, thereby sharpening up the interpretation of other VIMS data, especially the remainder of the same image.
Posted by: Jason W Barnes Nov 2 2009, 06:54 PM
QUOTE (rlorenz @ Nov 1 2009, 08:11 AM)
As I've remarked to you in person, it is totally cool. But what is the great science ? Since the specular point
is just that at any given instant, the geometry varies with time (i.e. the angle varies as the point tracks across
the surface, so you don't vary angle and position independently [this is also a problem in the radio equivalent -
the bistatic scattering experiment, results of which from T12 years ago have yet to be published] - maybe it's
not too much variation, I guess may depend on the specifics of a given observation.) If you
can resolve the brightness distribution around the specular point, then it is an interesting measure of roughness
across an assumed uniform structure like a lake, although is it any better than a SAR image of the same thing?
But a single pixel specular reflection is of limited utility, I think....
Not to be a (shiny) wet blanket, and I repeat, it is cool, but by itself it isnt telling us a lot about Titan unless I am
mistaken.
You are mistaken.
Saying that there's no information to be had from a single pixel would imply that, for instance, transiting extrasolar planets would tell us nothing, since they're just one pixel. In fact this is an apt analogy. I approach the Titan problem from the exact same standpoint -- that of a lightcurve. I fit the lightcurve using various critical parameters, from which I get the science. For instance, the lightcurve tells you the path that the specular reflection takes (using the RADAR basemap), from which I can infer the triaxial shape of the equipotential surface, along with other cool things like wave properties and the composition (okay, index of refraction) of the fluid. Stand by for the paper, it will probably be a few months yet with my twin babies arriving soon, but I think that by the end you'll agree that your above statement is one-minus-correct, perhaps not unlike your 1996 no-sand-dunes-on-Titan paper!
- Jason
Posted by: Jason W Barnes Nov 2 2009, 06:56 PM
QUOTE (ngunn @ Nov 1 2009, 12:25 PM)
Excuse a very basic question: would that be one pixel at one wavelength or do you get an IR spectrum for that pixel?
Well, there's a spectrum all right, but as the AGU abstract states, the specular reflection has no effect on the wavelengths shortward of 5um. So there's a spectrum within the 5um window, and upper limits below that.
- Jason
Posted by: rlorenz Nov 6 2009, 08:58 PM
QUOTE (Jason W Barnes @ Nov 2 2009, 01:54 PM)
You are mistaken.
Wot, are you a graduate from the Roger Yelle school of diplomacy or something..?
QUOTE
I fit the lightcurve using various critical parameters, from which I get the science. For instance, the lightcurve tells you the path that the specular reflection takes (using the RADAR basemap), from which I can infer the triaxial shape of the equipotential surface, along with other cool things like wave properties and the composition (okay, index of refraction) of the fluid.
Hmm, well, I'll stand by for the paper. But I still don't see how you can get wave properties and
composition independently for each point on your lightcurve : I can see how you might derive one
value for each if you assume the properties are spatially uniform along the specular track,
which they may or may not be (as casual inspection of a resolved image of sunglint on a terrestrial
lake or sea will tell you)
In any case, I hope this is just the first of many cool VIMS lakes results in coming years as the sun
rises over Titan's north. Hopefully the sunshine won't kick up too many clouds that you cant see anything..
Posted by: volcanopele Nov 6 2009, 09:26 PM
QUOTE (rlorenz @ Nov 6 2009, 01:58 PM)
Wot, are you a graduate from the Roger Yelle school of diplomacy or something..?
QUOTE
Hmm, well, I'll stand by for the paper. But I still don't see how you can get wave properties and
composition independently for each point on your lightcurve : I can see how you might derive one
value for each if you assume the properties are spatially uniform along the specular track,
which they may or may not be (as casual inspection of a resolved image of sunglint on a terrestrial
lake or sea will tell you)
Well, that presumes a single image of sunglint. Multiple images showing how the reflection changes with phase angle would help.
QUOTE
In any case, I hope this is just the first of many cool VIMS lakes results in coming years as the sun
rises over Titan's north. Hopefully the sunshine won't kick up too many clouds that you cant see anything..
Titan's like Kansas. The skies are never cloudy all day.
Posted by: Jason W Barnes Nov 7 2009, 05:54 AM
QUOTE (rlorenz @ Nov 6 2009, 01:58 PM)
Hmm, well, I'll stand by for the paper. But I still don't see how you can get wave properties and
composition independently for each point on your lightcurve : I can see how you might derive one
value for each if you assume the properties are spatially uniform along the specular track,
which they may or may not be (as casual inspection of a resolved image of sunglint on a terrestrial
lake or sea will tell you)
Agreed that there can't be composition and wave gradient distributions for each datapoint. But the composition of the lake should be the same for the whole lightcurve from mixing presumably, and if you assume a lower-order fit to the waves as a function of position, then you should be able to pull out some variations. Not from the present 4-point T58 lightcurve, mind you, but from potential future, tighter observations.
Also note that I would say that this technique has an advantage over the Wye et al. technique in that it does not require valuable closest-approach time -- the observations in question were a few hours after C/A IIRC.
- Jason
Edit -- Not to knock the Wye et al. work, which I think is awesome! Just that watching lakes looking for variations in waves would be expensive in terms of C/A time using that method.
Posted by: ngunn Nov 30 2009, 10:53 AM
Article on seasonal and longer term change:
http://www.sciencedaily.com/releases/2009/11/091129153401.htm
Source paper:
http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo698.html
Posted by: volcanopele Nov 30 2009, 05:17 PM
We shall see. I still think its seasonal.
Posted by: Jason W Barnes Nov 30 2009, 05:37 PM
QUOTE (volcanopele @ Nov 30 2009, 10:17 AM)
We shall see. I still think its seasonal.
But then where are the empty south polar lakes? Does the whole south pole fill up in southern winter? This is a problem with both the seasonal and longer-term migration of volatiles. I think that the total volume of methane/ethane transported between poles over seasonal and longer timescales is small, and that Kraken stays pretty much the way it is year-round.
Maybe.
- Jason
Posted by: volcanopele Nov 30 2009, 05:53 PM
Where are the south polar dry lakes? What do you think those low, flat areas are in the RADAR sar data that match up with ISS dark areas? That being said, the north polar region seems to have more dedicated lake basins while the south pole has mostly opportunistic playas (though there are a few of those up north too).
As for Kraken Mare, again, I think it is still plausible that Mezzoramia is the south polar version of that sea.
Posted by: ngunn Nov 30 2009, 06:00 PM
I don't have access to the full paper, but from what I have seen I like the idea of seasons superimposed on 'superseasons'. Nevertheless there must be other major factors involved as well, regional topography being an obvious one. For me the fact that there is still legitimate room for widely differing opinions on such a major matter is humbling and quite wonderful in itself.
Posted by: Jason W Barnes Nov 30 2009, 07:05 PM
QUOTE (volcanopele @ Nov 30 2009, 10:53 AM)
Where are the south polar dry lakes? What do you think those low, flat areas are in the RADAR sar data that match up with ISS dark areas?
I think they're dark areas. They could be anything.
If the ethane content of Kraken Mare is substantial, then there's just no way to move it around on seasonal timescales. Oded's Milankovic timescales, maybe.
- Jason
PS -- I can't even get a copy of this paper -- I guess we're not subscribed to Nature Geoscience here for some reason?
Posted by: Juramike Nov 30 2009, 07:51 PM
I really, really, like the idea of the longer term cycles. I think there's pretty good evidence of base level changes in both north polar regions (currently flooded) and in the south polar regions (currently drier).
A long term cycle will allow polar lakes to dry out as the solvent level drops, while the occasional seasonal rains will incise channels in the dry lakebeds.
-Mike
Posted by: ngunn Nov 30 2009, 08:32 PM
I've been checking authors' websites, but had no luck finding a free version of the paper. However I did find this fuller version of the article, with nice illustrations:
http://www.gps.caltech.edu/~oa/titanlakes.shtml
Posted by: volcanopele Nov 30 2009, 08:50 PM
Very nice article! Thanks for the link. Though, hmm, there are a lot more empty lakes down in the south polar region than mapped...
Posted by: ngunn Nov 30 2009, 09:06 PM
QUOTE (Jason W Barnes @ Nov 30 2009, 07:05 PM)
If the ethane content of Kraken Mare is substantial, then there's just no way to move it around
If the lakebeds are porous maybe the ethane doesn't have to move between hemispheres on either timescale. When evaporation concentrates ethane in a lake it may be able to diffuse into the less concentrated subsurface alkanofer. Methane diffusing the other way would return to the lake, ensuring that evaporation could continue until the lake appears dry. Of course on this model you have to move even greater volumes of methane around - to lower not just the lakes but the surrounding alkanofer too.
Posted by: Juramike Nov 30 2009, 09:46 PM
QUOTE (volcanopele @ Nov 30 2009, 03:50 PM)
Though, hmm, there are a lot more empty lakes down in the south polar region than mapped...
(I think so, too...a lot more. Topographical information for the S Polar regions will be really helpful.)
Posted by: Juramike Nov 30 2009, 09:54 PM
QUOTE (ngunn @ Nov 30 2009, 04:06 PM)
Of course on this model you have to move even greater volumes of methane around - to lower not just the lakes but the surrounding alkanofer too.
True. But if the subsurface is extremely porous, you may only need to move a small percentage of the overall amount to effect a large change in the base level. Picture a 1 km deep porous bed: 10% change would give you 100 m change in solvent level (ignoring volume of porous material).
So while the absolute amount of methane to move from pole to pole is large, the relative amount compared to the (still unknown) subsurface reservoir could be fractional.
Posted by: ngunn Nov 30 2009, 10:27 PM
Yes. And if the lakes 'breathe' into and out of that greater reservoir we have to think of them very differently from the way we think about terrestrial lakes. A closer terrestrial analogy might be dune slacks which are common near where I live. I'm not sure how current that term is but it refers to pools in depressions within areas of coastal sand dunes.
Posted by: rlorenz Dec 1 2009, 11:23 PM
QUOTE (Jason W Barnes @ Nov 30 2009, 02:05 PM)
If the ethane content of Kraken Mare is substantial, then there's just no way to move it around on seasonal timescales. Oded's Milankovic timescales, maybe.
Right. Likely difficult to determine remotely (detecting that ethane is there is one thing, as for
VIMS/Ontario ; measuring an abundance is another thing. In principle microwave radiometry might
be able to do it (or RSS bistatic), might need assumptions about roughness or depth etc.)
Titan Mare Explorer will do a bang-up job on lake composition...
If Kraken is deep (as its size suggests it should be) it is hard to see that it could be seasonal, regardless of
composition.
I have been on a jihad for some time to stress Croll-Milankovich. James Croll figured it all out in the
1860s. Milankovich just came along later and did the astronomical math a bit better. (Croll I think was the
first to calculate how much colder Europe would be without the Gulf stream, for example ; he studied
boulder clays and geological evidence, as well as the astronomical forcing and heat budget.)
Posted by: remcook Dec 2 2009, 08:35 AM
So, what is new in this paper? The speculation about the Croll-Milankovich cycle? (yes there probably is an effect and it is a valid hypothesis, but do we really see any evidence for it happening? Erasing craters at the poles are happening anyway, regardless of the cycle, since there is methane rain on either side, right? Plus, there might be other erosion mechanisms at work. Not sure you can tell from a dozen craters.) Didn't we already know that there are more lakes in the north, that the topography is similar and that the northern winter is harsher than the southern? Maybe someone can explain in a bit more detail?
Posted by: Jason W Barnes Dec 2 2009, 05:54 PM
QUOTE (rlorenz @ Dec 1 2009, 04:23 PM)
Titan Mare Explorer will do a bang-up job on lake composition...
Assuming that the lake really IS deep enough so as not to volatilize entirely and head south for the summer.
- Jason
Posted by: Juramike Dec 2 2009, 06:33 PM
Splash, schplat, or crunch?
Posted by: ngunn Dec 2 2009, 10:01 PM
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 . . .
Posted by: marsbug Dec 3 2009, 12:24 PM
QUOTE (Juramike @ Dec 2 2009, 07:33 PM)
Splash, schplat, or crunch?
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!
Posted by: rlorenz Dec 6 2009, 05:33 PM
QUOTE (marsbug @ Dec 3 2009, 07:24 AM)
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.
....
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/viscositywaves_accepted.pdf
Posted by: ngunn Dec 6 2009, 06:49 PM
What a fascinating paper! Thanks for posting it here.
Posted by: antipode Dec 7 2009, 07:43 AM
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
Posted by: marsbug Dec 7 2009, 10:54 AM
Thanks, thats kept my imagination busy for a good while!
Posted by: stevesliva Dec 7 2009, 10:16 PM
QUOTE (rlorenz @ Dec 6 2009, 12:33 PM)
Well, Steve Wall has a paper submitted on Ontario with an interpretation of possible wave action on the shores
That's from the goolaciers calving into the glake.
Posted by: stewjack Dec 8 2009, 03:56 AM
QUOTE (stevesliva @ Dec 7 2009, 05:16 PM)
That's from the goolaciers calving into the glake.
Posted by: nprev Dec 8 2009, 04:47 AM
Gross.
Posted by: Webscientist Dec 8 2009, 09:07 PM
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/imagedetails/index.cfm?imageId=2733
Posted by: Vultur Dec 12 2009, 05:40 PM
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?
Posted by: Juramike Dec 12 2009, 06:26 PM
QUOTE (Vultur @ Dec 12 2009, 12:40 PM)
...is it possible that *just* the methane moves?
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.)
Posted by: Ron Hobbs Dec 17 2009, 09:16 PM
Well it looks like whatever the physical characteristics, the stuff in the lakes exhibit specular reflection ... and rather dramatically.
http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20091217/
Today is the day for dramatic pictures!
Posted by: volcanopele Dec 17 2009, 09:21 PM
Cool, with the exception of the Kraken Mare part
Posted by: elakdawalla Dec 18 2009, 04:24 AM
What's wrong with the Kraken Mare part?
Posted by: volcanopele Dec 18 2009, 05:26 AM
The Glint wasn't found in Kraken Mare, but a large lake to the west of it.
Posted by: volcanopele Dec 18 2009, 06:05 AM
Here's a map:
Posted by: nprev Dec 18 2009, 06:42 AM
Thanks, Jason. Not gonna ask why wrt the error, but do very much appreciate the correction & accuracy!
Posted by: Jason W Barnes Dec 18 2009, 10:14 AM
QUOTE (volcanopele @ Dec 17 2009, 11:05 PM)
They sure look connected to me, man. I don't see the problem.
- Jason
Posted by: volcanopele Dec 18 2009, 10:27 AM
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
Posted by: ngunn Dec 18 2009, 10:30 AM
That's fantastic - I really wasn't expecting the image itself to be so striking.
Posted by: Jason W Barnes Dec 18 2009, 02:18 PM
QUOTE (volcanopele @ Dec 18 2009, 03:27 AM)
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.
Maybe so, but there's no continuous RADAR coverage and I don't see it in the image you posted.
- Jason
Posted by: stevesliva Dec 18 2009, 05:00 PM
They'll just have to call it Kraken-egg Lacus if there's no connection.
Posted by: volcanopele Dec 18 2009, 07:44 PM
QUOTE (Jason W Barnes @ Dec 18 2009, 07:18 AM)
Maybe so, but there's no continuous RADAR coverage and I don't see it in the image you posted.
- Jason
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.
Posted by: Enceladus75 Dec 18 2009, 10:12 PM
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.
Posted by: HughFromAlice Dec 19 2009, 09:45 AM
QUOTE (Enceladus75 @ Dec 19 2009, 07:42 AM)
That image is stunning and iconic..... 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
!!!).
Posted by: nprev Dec 19 2009, 10:11 AM
QUOTE (HughFromAlice @ Dec 19 2009, 01:45 AM)
If such a small lake throws such a specular reflection, then ....!!!
...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.
Posted by: HughFromAlice Dec 19 2009, 12:47 PM
Small....... comparatively!!!
Posted by: imipak Dec 19 2009, 01:19 PM
The BBC has a http://news.bbc.co.uk/1/hi/sci/tech/8409052.stm 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.
Posted by: volcanopele Dec 19 2009, 05:58 PM
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
Posted by: scalbers Dec 19 2009, 07:04 PM
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?
Posted by: titanicrivers Dec 19 2009, 09:13 PM
QUOTE (volcanopele @ Dec 18 2009, 12:05 AM)
Here's a map:
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).
Posted by: djellison Dec 20 2009, 02:52 PM
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.
Posted by: peter59 Dec 20 2009, 03:13 PM
"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."
http://ciclops.org/view/6082/Rev123
Posted by: elakdawalla Dec 20 2009, 04:46 PM
QUOTE (volcanopele @ Dec 19 2009, 09:58 AM)
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
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?
Posted by: scalbers Dec 20 2009, 05:47 PM
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/commons/2/29/Lake_Erie_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?
Posted by: Jason W Barnes Dec 20 2009, 07:55 PM
QUOTE (elakdawalla @ Dec 20 2009, 09:46 AM)
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?
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 . . .
QUOTE (elakdawalla @ Dec 20 2009, 09:46 AM)
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?
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
Posted by: elakdawalla Dec 20 2009, 08:26 PM
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
Posted by: scalbers Dec 20 2009, 09:56 PM
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 http://en.wikipedia.org/wiki/Fresnel_equations. As an example glass at normal incidence has about a 4% reflection. We can calculate the somewhat lower values for http://en.wikipedia.org/wiki/File:Water_reflectivity.jpg, 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
Posted by: rlorenz Dec 20 2009, 11:47 PM
QUOTE (scalbers @ Dec 19 2009, 02:04 PM)
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? .....
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?
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.
Posted by: nprev Dec 21 2009, 12:02 AM
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.
Posted by: scalbers Dec 21 2009, 12:19 AM
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.
Posted by: titanicrivers Dec 21 2009, 01:50 AM
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.
Posted by: rlorenz Dec 21 2009, 01:56 AM
QUOTE (nprev @ Dec 20 2009, 07:02 PM)
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
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.
Posted by: nprev Dec 21 2009, 02:15 AM
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?
Posted by: Jason W Barnes Dec 21 2009, 07:04 AM
QUOTE (rlorenz @ Dec 20 2009, 05:47 PM)
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).
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 -- http://barnesos.net/publications/papers/Oblateness.pdf, http://barnesos.net/publications/papers/TransitingRings.ApJ.pdf, http://barnesos.net/publications/papers/2009.11.ApJ.Barnes.Wind.Shapes.of.EGPs.pdf, http://barnesos.net/publications/papers/2009.11.ApJ.Barnes.FastRotatingStars.pdf, http://barnesos.net/publications/papers/2007.09.PASP.Barnes.eccentric.transiting.planets.pdf . . .
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
Posted by: AndyG Dec 21 2009, 10:51 AM
QUOTE (rlorenz @ Dec 21 2009, 01:56 AM)
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...
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
Posted by: rlorenz Dec 21 2009, 01:19 PM
More iconic than useful..
QUOTE (Jason W Barnes @ Dec 21 2009, 02:04 AM)
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.
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.
QUOTE
By your criterion, signal not spatially resolved, transits of extrasolar planets are useless.
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.
QUOTE
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.
It isn't a discovery. It's a confirmation (the image release - which is what prompted the discussion - even says that).
Posted by: djellison Dec 21 2009, 03:17 PM
Anyone for popcorn
Posted by: Mongo Dec 21 2009, 05:03 PM
Fight! Fight! Fight! Fight!
Posted by: rlorenz Dec 22 2009, 01:30 AM
QUOTE (djellison @ Dec 21 2009, 10:17 AM)
Anyone for popcorn
Actually, Doug, I half-expected you to kill the thread as becoming too inflamed... Jason and
I are good at what we do in part because we believe in it, are passionate about it, and,
sometimes, defensive about it.
Anyway, the Titan-ExtraSolarPlanets analogy is kind of interesting (I've noticed, passim,
that quite a number of Exoplanet talks now show Titan, sometimes a hazy crescent to represent
photochemical haze alluding to early Earth, or sometimes a surface albedo image just as a
conveniently 'wierd' planetary background. I bet the Titan sunglint image gets used a lot
now in exoplanet talks).
Between about 1990 and late 1994, of course, lightcurves (both near-IR and radar) were
all the information we had about Titan's surface. Not that the HST imaging in 1994 really
brought us that much further forward - it told us there are bright bits and dark bits, but the
lightcurve already told us that in a 1-d sense.
In retrospect I made a scientific goof by not following to completion a toy project that I started with
Albert Haldemann and Greg Black (both radar astronomers) in the late 1990s. Albert asked the
question of how would the Earth look if the Arecibo dish were on Titan pointing at Earth. So I set
up a model to wrap a map of terrain types on a globe with different scattering functions
and generate synthetic disk-integrated radar albedo, which also included stuff like ocean glint.
But it was kind of an academic question and I never got round to finishing it. If I had been
smart, as soon as people started talking about exoplanet lightcurves, I could have easily
adapted the code to do sun glint rather than radar and could have squeezed off a neat little paper.
I think the EPOXI crowd have more or less redone all that work now. Oh well..
Posted by: ngunn Dec 22 2009, 11:13 AM
Is it safe to come out now?
For me millimeter-smooth and micron-smooth are significantly different bits of information, even if they do probably have a common explanation. That would make this a discovery in one sense and a confirmation in another.
Such amazing revelations, such a wonderful time to be alive! Having real professional comment and debate on this forum is a great bonus for the rest of us. All the people who in different ways make this possible deserve our congratulations and heartfelt thanks.
Posted by: Jason W Barnes Dec 22 2009, 06:02 PM
QUOTE (ngunn @ Dec 22 2009, 05:13 AM)
Is it safe to come out now?
Oh, you needn't worry -- my Ralph-seeking smart bombs rarely cause collateral damage
I'm still reeling from when Ralph, as a thesis committee-member, called my Ph.D. dissertation a "tour-de-force of high school geometry"! So yeah, we do this, and have for years -- thanks for putting up with it . . .
- Jason
Posted by: nprev Dec 22 2009, 09:05 PM
Well, as long as there's some smiling involved!
Productive dynamics are where you find them...
Posted by: ngunn Dec 22 2009, 09:39 PM
QUOTE (Jason W Barnes @ Dec 22 2009, 06:02 PM)
as a thesis committee-member
I'm just glad neither of you was called in to examine mine.
(Actually, you're both too young.)
Posted by: PFK Dec 23 2009, 12:04 AM
QUOTE (Jason W Barnes @ Dec 22 2009, 06:02 PM)
I'm still reeling from when Ralph, as a thesis committee-member, called my Ph.D. dissertation a "tour-de-force of high school geometry"!
Ouch! Still, I had a referee's comment on a paper way back during my PhD that simply read "this work should not be published anywhere". Rest assured we still shifted it
Posted by: belleraphon1 Dec 23 2009, 02:43 AM
Having peanuts and beer!
Agree with ngunn's sentiments.,"Having real professional comment and debate on this forum is a great bonus for the rest of us."
I love the discourse.
Luv this forum.
Craig
Posted by: rlorenz Dec 23 2009, 03:41 AM
QUOTE (Jason W Barnes @ Dec 22 2009, 01:02 PM)
I'm still reeling from when Ralph, as a thesis committee-member, called my Ph.D. dissertation a "tour-de-force of high school geometry"! So yeah, we do this, and have for years
Well, yeah, tee hee. I mean, you did the math all nice and stuff, and used fancy words like 'extrasolar planet
transit lightcurve', but it did boil down to 'star shines, planet gets in the way, see less starlight...'
I dare say when all is said and done, Professor Barnes will leave his mark on a student or two at their defenses himself.
Posted by: scalbers Dec 23 2009, 03:15 PM
QUOTE (scalbers @ Dec 21 2009, 12:19 AM)
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.
Looks like Fridger Schrempp (one of the Celestia developers) is getting a head start on this. He is constructing a specular reflection map - simply a pixel map showing the locations of known lakes that can be used in Celestia.
http://forum.celestialmatters.org/viewtopic.php?t=358
EDIT: Here is a paper on http://tao.cgu.org.tw/pdf/v171p253.pdf and another on http://ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel2%2F2951%2F8342%2F00363898.pdf&authDecision=-203 in Earth's oceans. I would suppose with the sun being about 3 arcmin diameter from Titan, the surface footprint (assuming a perfectly smooth surface) would be about a kilometer on the narrow direction (longitude) and a few kilometers in the wider direction (latitude). This is pretty small, so the dominant factor in spreading would be the roughness from waves or whatever.
I wrote some software in my day job to calculate sun-glint locations in geostationary weather satellite images, so in theory I could hook it up with a Cassini Titan ephemeris to try and calculate sun-glint surface locations.
Posted by: belleraphon1 Jan 24 2010, 08:08 PM
Apologies if someone has already posted the Wall et al paper.
"The active shoreline of Ontario Lacus, Titan: a morphological study of the lake and its surroundings"
http://www.gps.caltech.edu/~mitri/articoli/wall_2010.pdf
"Abstract
Of more than 400 filled lakes now identified on Titan, the first and largest reported in the southern latitudes is Ontario Lacus, which is dark in both infrared and microwave. Here we describe recent observations including synthetic aperture radar (SAR) images by Cassini’s radar instrument (λ=2 cm) and show morphological evidence for active material transport and erosion. Ontario Lacus lies in a shallow depression, with greater relief on the southwestern shore and a gently sloping, possibly wave-generated beach to the northeast. The lake has a closed internal drainage system fed by Earth-like rivers, deltas and alluvial fans. Evidence for active shoreline processes, including the wave-modified lakefront and deltaic deposition, indicates that Ontario is a dynamic feature undergoing typical terrestrial forms of littoral modification."
Nice figure of Ontario on page 15.
Craig
Posted by: Phil Stooke Jan 24 2010, 08:30 PM
Nice! And abstract 1466 at LPSC has a similar Ontario Lacus image. Or you can visit Toronto and see the real thing.
Phil
Posted by: belleraphon1 Jan 25 2010, 02:16 AM
Phil....
I live about 20 miles from Lake Erie (another inland sea). . Walk the ice ramps in the winter time... I could almost be on Titan. Except the liquid phase is molten H2O, there is no smust or smurst, and usually not a hint of methane!
Craig
Posted by: volcanopele Mar 1 2010, 01:15 AM
The VIMS team has published a short paper in GRL on their specular reflection observation:
Stephan, K., R. Jaumann, R. H. Brown, J. M. Soderblom, L. A. Soderblom, J. W. Barnes, C. Sotin, C. A. Griffith, R. L. Kirk, K. H. Baines, B. J. Buratti, R. N. Clark, D. M. Lytle, R. M. Nelson, and P. D. Nicholson (2010),
Specular reflection on Titan: Liquids in Kraken Mare,
Geophys. Res. Lett., doi:10.1029/2009GL042312, in press.
Posted by: Jason W Barnes Mar 1 2010, 07:04 AM
QUOTE (volcanopele @ Feb 28 2010, 07:15 PM)
The VIMS team has published a short paper in GRL on their specular reflection observation:
Stephan, K., R. Jaumann, R. H. Brown, J. M. Soderblom, L. A. Soderblom, J. W. Barnes, C. Sotin, C. A. Griffith, R. L. Kirk, K. H. Baines, B. J. Buratti, R. N. Clark, D. M. Lytle, R. M. Nelson, and P. D. Nicholson (2010),
Specular reflection on Titan: Liquids in Kraken Mare,
Geophys. Res. Lett., doi:10.1029/2009GL042312, in press.
Link to http://barnesos.net/publications/papers/2010.04.Stefan.GRL.Specular.pdf on my site.
I hadn't realized it was out in the "papers in print" yet even! Good eye ISS Jason . . .
- VIMS Jason
Posted by: volcanopele Mar 1 2010, 08:01 AM
no problem. Though it does remind me that I should make some graphics showing the geography around Kraken Mare for the workshop next week
Great work VIMS Jason and the rest of the VIMS group!
Posted by: titanicrivers Mar 1 2010, 08:03 AM
Very nice paper! Thanks for posting here Jason. There’s also an ASC 2010 meeting abstract with many of the same authors and some additional location maps. http://www.lpi.usra.edu/meetings/abscicon2010/pdf/5149.pdf. In that abstract
there’s a location map (Fig 2) that shows the probable glint source locations. The strongest glint appears to be pretty much the same area just ‘off shore’ from the + sign in this estimate from post # 145 shown below. Whether this is a bay of Kraken Mare or a separate unnamed large lake (unofficially referred to as Sunglint Lake) remains speculative.
Posted by: Jason W Barnes Mar 1 2010, 08:06 AM
QUOTE (titanicrivers @ Mar 1 2010, 02:03 AM)
Very nice paper! Thanks for posting here Jason. There’s also an ASC 2010 meeting abstract with many of the same authors and some additional location maps. http://www.lpi.usra.edu/meetings/abscicon2010/pdf/5149.pdf. In that abstract
there’s a location map (Fig 2) that shows the probable glint source locations. The strongest glint appears to be pretty much the same area just ‘off shore’ from the + sign in this estimate from post # 145 shown below. Whether this is a bay of Kraken Mare or a separate unnamed large lake (unofficially referred to as Sunglint Lake) remains speculative.
We've got a name request in for the sunglint lake. I'll don't want to leak the requested name, but I'll let you know when it's been approved.
- VIMS Jason
Posted by: Jason W Barnes Mar 1 2010, 08:11 AM
QUOTE (titanicrivers @ Mar 1 2010, 02:03 AM)
Your RADAR map is incomplete, I think. Take a look at the RADAR T30 S02 data in the PDS -- it extends the strip to show the SE corner of sunglint lake. Makes a pretty good case that the lake is separate, but still not 100% for sure.
- VIMS Jason
Posted by: titanicrivers Mar 1 2010, 07:08 PM
QUOTE (Jason W Barnes @ Mar 1 2010, 02:11 AM)
Your RADAR map is incomplete, I think. Take a look at the RADAR T30 S02 data in the PDS -- it extends the strip to show the SE corner of sunglint lake. Makes a pretty good case that the lake is separate, but still not 100% for sure.
- VIMS Jason
I realized that when I looked at Figure 2 in the ASC 2010 meeting abstract http://www.lpi.usra.edu/meetings/abscicon2010/pdf/5149.pdf. Fig 2a shows the same radar swaths (as they appeared in VP's polar maps that I used) however Fig2b shows the extension of radar swaths to fill in the SE portion of Sunglint Lake as you point out above.
BTW: I didn't find the same glint mapping figures in your post of the paper as appeared in the ASC abstract, yet it seemed your paper was referring to such in the body of the text. Perhaps my browser didn't download that Figure properly from your paper.
Posted by: volcanopele Mar 1 2010, 07:14 PM
QUOTE (volcanopele @ Mar 1 2010, 01:01 AM)
no problem. Though it does remind me that I should make some graphics showing the geography around Kraken Mare for the workshop next week
Hmm, not sure why I kept thinking that the TSWG workshop is next week... regardless, I should try to print out some of my cartographic products (at least to remind people yes, we see the surface, no it's as colorful as what VIMS can see, but it can still look cool... and shows distinct boundaries of features before RADAR can see them ;-)
Posted by: hendric Mar 2 2010, 02:39 PM
Dumb Q, but could Cassini detect specular reflections of Saturn in the lakes? Or is it too "faint" in comparison to the sun to be visible?
Posted by: Jason W Barnes Mar 2 2010, 06:15 PM
QUOTE (hendric @ Mar 2 2010, 08:39 AM)
Dumb Q, but could Cassini detect specular reflections of Saturn in the lakes? Or is it too "faint" in comparison to the sun to be visible?
Interesting idea. I haven't thought about it before. My guess is that it wouldn't be a very impressive observation, but I should do the calculation.
- VIMS Jason
Posted by: hendric Mar 2 2010, 10:47 PM
If there is one, perhaps you could use it to monitor the evaporation of liquids from the dark pole? Saturn's brightness won't change significantly over the course of the XXM.
Posted by: ngunn Mar 2 2010, 11:14 PM
This sounds like a great idea to me. It would have to be a nightside image though, so the sooner the better. With most of the lakes being in the north plus darkness retreating from high northern latitudes and the huge amount of scattering that occurs in Titan's atmosphere spreading twilight so far around the globe the chances may already be slender. There's always Ontario, of course.
Posted by: Hungry4info Mar 3 2010, 04:34 AM
What could we learn from such an observation that seeing the reflection of the sun itself wouldn't?
Posted by: hendric Mar 3 2010, 02:58 PM
Well, Saturn is much larger in the sky than the sun from Titan's surface, so the odds of a reflection are much higher. If it is possible to do multiple targettings over the XXM then we could see if the reflection profile changes brightness or color.
I don't think it could be done during a night pass, because of the geometry. I think the best bet is to try during a half-full Saturn phase as viewed from Titan. That alone might make it unlikely, because of the brightness of the rest of the planet in daylight.
Posted by: rlorenz Mar 6 2010, 08:05 PM
QUOTE (hendric @ Mar 3 2010, 09:58 AM)
Well, Saturn is much larger in the sky......That alone might make it unlikely, because of the brightness of the rest of the planet in daylight.
And whatever the geometry, the light is down by a factor of (1/20)^2 = 400 since
Saturn's light is spread over a sphere equal to Titan's radius. Pulling that signal out
from the scattered light in Titan's atmosphere could be a challenge.
Now if only there were some way of illuminating the surface any time you wanted, with
some, like, 'magic' light that wasnt scattered by the atmosphere..... oh, wait...
Posted by: volcanopele Mar 29 2010, 08:44 PM
QUOTE (Jason W Barnes @ Mar 1 2010, 01:06 AM)
We've got a name request in for the sunglint lake. I'll don't want to leak the requested name, but I'll let you know when it's been approved.
- VIMS Jason
The name has been approved. The sunglint lake is now known as Jingpo Lacus, after a lake in China.
Coincidently (or not actually, it was quite intentional...), Jingpo Lacus means "Mirror Lake"
http://en.wikipedia.org/wiki/Jingpo_Lake
Posted by: ngunn Mar 29 2010, 08:56 PM
Looks like a nice place:
http://scenery.cultural-china.com/chinaWH/upload/upfiles/2008-12/25/culturalchina98f32e0eff8958933454.jpg
Posted by: Jason W Barnes Mar 30 2010, 08:07 PM
QUOTE (volcanopele @ Mar 29 2010, 02:44 PM)
Coincidently (or not actually, it was quite intentional...), Jingpo Lacus means "Mirror Lake"
Yeah -- intentional.
At least something good out of not having had this lake named earlier. Gave us the chance to name it after the specular reflection discovery.
- Jason
Posted by: scalbers Oct 2 2010, 06:28 PM
This is a nice visualization of Ontario Lacus:
http://www.jpl.nasa.gov/video/index.cfm?id=912
Posted by: djellison Oct 3 2010, 01:04 AM
I should hope so - with Randy Kirk et.al's data and Steve Wall's scientific guidance - I made it It was my first assignment on lab.
Posted by: HughFromAlice Oct 17 2010, 10:54 AM
QUOTE (djellison @ Oct 3 2010, 10:34 AM)
my first assignment on lab.
Well, you did a bloody good job with what was probably quite slender data. What an amazing first assignment to be given!!!
Posted by: djellison Oct 17 2010, 05:20 PM
Let's just say the DTM was quite low res, and leave it at that
Posted by: Tom Tamlyn Oct 17 2010, 10:12 PM
Beautiful, Doug!
Was it prepared primarily for outreach, or for the use of project scientists? Or both?
TTT
Posted by: djellison Oct 18 2010, 06:12 AM
Oh, just for outreach, but it was great working with a scientist to get it as authentic as we thought we could from the data in hand.
Posted by: climber Oct 18 2010, 10:49 AM
Scientist are human too and I'm sure they stared at the fly over as much as I did. Very inspiring...specialy the "Bay view" near the end.
More of these please
Posted by: centsworth_II Jan 6 2011, 05:56 AM
QUOTE (scalbers @ Oct 2 2010, 01:28 PM)
This is a nice visualization of Ontario Lacus:
http://www.jpl.nasa.gov/video/index.cfm?id=912
http://blogs.discovermagazine.com/discoblog/2011/01/05/if-keha-was-into-astrobiology-she-still-wouldnt-have-made-this-video/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+DiscoverDiscoblog+%28Discoblog%29
(at 57 seconds into the video)
Posted by: ngunn Jan 13 2011, 02:30 PM
New VIMS paper on specular reflection lightcurves courtesy of VIMS Jason: http://barnesos.net/publications/papers/2011.01.Icarus.Barnes.Specular.Waves.pdf
Posted by: Jason W Barnes Jan 14 2011, 04:39 PM
QUOTE (ngunn @ Jan 13 2011, 07:30 AM)
New VIMS paper on specular reflection lightcurves courtesy of VIMS Jason: http://barnesos.net/publications/papers/2011.01.Icarus.Barnes.Specular.Waves.pdf
This is actually the same one from post #166 above, only now in official format and out in the dead-tree version of the journal. Seems like a long lag, I know. And this came out pretty fast, for Icarus!
- Jason
Posted by: ngunn Jan 14 2011, 06:33 PM
Same science I guess, but some different authors, different text and different diagrams. I particularly like the new illustrations. Anyhow it's such a great subject I'm happy to read about it all over again. Thanks once more for making it available.
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