Today's big news?
http://ciclops.org/view/5471/CASSINI_FINDS...ILL_TITAN_LAKES

Changes in the south polar region were announced late last year. Is there more to this story now??

Aah, there's this:
http://saturn.jpl.nasa.gov/multimedia/imag...11146-th120.jpg

and this:
http://saturn.jpl.nasa.gov/multimedia/imag...11147-th120.jpg

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.

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.

That's brilliant, thanks VP.

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

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.

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

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!

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.p...st&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.

Click to view attachment

LPSC abstracts will be out soon - there will be something for you there

Excellent!!

Oh, goodygoodygoody...Santa Ralph hints that a bit of Christmas is coming early this year!

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.

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 !!!

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?

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... :-{

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.

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)

WTF? Program committee on crack is what that is.

- Jason

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.

Great - another potentially variable lake property accessible for occasional monitoring by Cassini. I look forward to the first results.

VIMS Ontario Lacus paper is now out in print from either Icarus ( http://www.sciencedirect.com/science?_ob=A...b490613a43ebb98 )
or from my website ( http://www.barnesos.net/publications/paper...s.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

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.

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.

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

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/dn1766...ping-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!).

Hey! I got lucky and got the whole article. (Does that make me a criminal?)

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

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.

Minus the ducks. Their wake would have ruined the 3mm factor

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)

BIG changes observed at Ontario Lacus in the 4th abstract here:

http://www.abstractsonline.com/plan/ViewSe...51-9adfcf8a8005

Hmm... don't seem to be getting that link to work nigel. Any other link to follow?

I confirm.

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.

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

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

How well do the ISS and RADAR 'shorelines' correlate for the northern lakes?

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.

So when will us common folk get to see the T57/T58 SAR RADAR results?

See if I can get this link to the goodies to work!
(nope, will try another)

http://www.abstractsonline.com/plan/start....08CED373A512%7D

That one seems to work.

I've edited my previous post 42 to correct a numerical error.

When will we see the SAR? I'd guess around conference time.

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!

Well, hopefully they will broadcast the oral sessions online like they did last year.

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/paper...s.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.

NASA Cassini Radar Observes Seasonal Change in Titan's North Pole
New Evidence of Seasonal Change on Titan

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'.