Anyone for popcorn

Fight! Fight! Fight! Fight!

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..

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.

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

Well, as long as there's some smiling involved!

Productive dynamics are where you find them...

I'm just glad neither of you was called in to examine mine.
(Actually, you're both too young.)

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

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

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.

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 sun glint size and another on relationship to wind induced waves 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.

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

Nice! And abstract 1466 at LPSC has a similar Ontario Lacus image. Or you can visit Toronto and see the real thing.

Phil

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

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 the paper on my site.

I hadn't realized it was out in the "papers in print" yet even! Good eye ISS Jason . . .

- VIMS Jason

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!

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.
Click to view attachment

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

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.

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 ;-)

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

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.

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.

What could we learn from such an observation that seeing the reflection of the sun itself wouldn't?

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.

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...

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

Looks like a nice place:
http://scenery.cultural-china.com/chinaWH/...f8958933454.jpg

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

This is a nice visualization of Ontario Lacus:

http://www.jpl.nasa.gov/video/index.cfm?id=912

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.

Well, you did a bloody good job with what was probably quite slender data. What an amazing first assignment to be given!!!

Let's just say the DTM was quite low res, and leave it at that

Beautiful, Doug!

Was it prepared primarily for outreach, or for the use of project scientists? Or both?

TTT

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.

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

Doug's been sampled!
(at 57 seconds into the video)
Click to view attachment

New VIMS paper on specular reflection lightcurves courtesy of VIMS Jason: http://barnesos.net/publications/papers/20...cular.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

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.