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Titan's changing lakes
djellison
post Dec 21 2009, 03:17 PM
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Anyone for popcorn smile.gif
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Mongo
post Dec 21 2009, 05:03 PM
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Fight! Fight! Fight! Fight! huh.gif
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rlorenz
post Dec 22 2009, 01:30 AM
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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..

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ngunn
post Dec 22 2009, 11:13 AM
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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. smile.gif

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.

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Jason W Barnes
post Dec 22 2009, 06:02 PM
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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 wink.gif

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 . . . smile.gif

- Jason
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nprev
post Dec 22 2009, 09:05 PM
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Well, as long as there's some smiling involved! smile.gif

Productive dynamics are where you find them...



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ngunn
post Dec 22 2009, 09:39 PM
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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.)
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PFK
post Dec 23 2009, 12:04 AM
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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 laugh.gif
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belleraphon1
post Dec 23 2009, 02:43 AM
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Having peanuts and beer! smile.gif

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
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rlorenz
post Dec 23 2009, 03:41 AM
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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.
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scalbers
post Dec 23 2009, 03:15 PM
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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 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.
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belleraphon1
post Jan 24 2010, 08:08 PM
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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 Cassiniís 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
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Phil Stooke
post Jan 24 2010, 08:30 PM
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Nice! And abstract 1466 at LPSC has a similar Ontario Lacus image. Or you can visit Toronto and see the real thing.

Phil


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belleraphon1
post Jan 25 2010, 02:16 AM
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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! laugh.gif

Craig
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volcanopele
post Mar 1 2010, 01:15 AM
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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.


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