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Posted by: volcanopele Jul 24 2006, 09:33 PM

Much to my surprise, a chunk of the T16 Sar swath as been released:

http://photojournal.jpl.nasa.gov/catalog/PIA08630

An abundance of lakes can been seen. Some appear to be crater lakes (or sinkholes), like the lake at far left on the top cutout. That lake appears similar to Crater Lake in Oregon, with a little island in the middle (you can kinda see the attenuation of the signal surrounding the island as the methane gets deeper). Some lakes appear quite distinctive from the surrounding terrain, like the features on the right part of the bottom cutout.

Posted by: AlexBlackwell Jul 24 2006, 09:39 PM

I know Jason and some of the other Yahoo! planetary_sciences alumni will remember the following wager that someone made with a few of us just over two years ago:

"I have wagered $20 that Titan's surface lacks Cassini-resolvable bodies of liquid."

Posted by: volcanopele Jul 24 2006, 09:42 PM

Was that me? I forget now

But to be honest, they didn't find "bodies of liquid", they found features whose morphology is best explained by lakes... Though finding features consistent dry lake beds (with presumably large pebbles) next to smooth terrain in the same basins, would seem to clinch it (for me anyway).

Posted by: AlexBlackwell Jul 24 2006, 09:45 PM

No, it was someone else. Both you and I took the bet :-) See Messages #14584 and #15285 in the old group.

Posted by: ugordan Jul 24 2006, 09:47 PM

Wow, this is it!
Finally here we have a body we can (almost certainly) say has ponds of liquid, other than our fair planet!
Theorizing lakes exist is one thing, actually seeing them is another. Maybe I'm making too much of this, but this feels to me as equally important as seeing Enceladean plumes clearly for the first time. We're at the mid-point of the primary mission and Titan just became a little more familiar place.

Hats off to the RADAR team for a swift release!

Posted by: David Jul 24 2006, 09:48 PM

This is fantastic stuff. I'd be even happier if I could see one of the surface channels discharging into a lake so as to remove all doubt...

Posted by: djellison Jul 24 2006, 09:59 PM

The largest body in the top right actually has some channels around its periphery - within the confines of what one might call the 'lake' but between that edge and the darkest part of the lake in the middle - you can just see them

Doug

Posted by: The Messenger Jul 24 2006, 10:02 PM

Can it be stated with certainty that these are not liquid water lakes, or perhaps frozen water lakes?

18 months ago everyone was quit certain that there could not be liquid water geysers near the south pole of Enceladus. Do we have enough spectral/temperature data to say this is not water near the north pole of Titan?

Posted by: volcanopele Jul 24 2006, 10:20 PM

They do get radiometry at the same time they acquire SAR coverage. If these were lakes of liquid water, they would of course show up as VERY warm areas compared to what they should be.

While I would dismiss the notion that these are water lakes until we hear otherwise from the RADAR team, I do note that some of the lake depressions look an awful lot like Ionian calderas.

Posted by: belleraphon1 Jul 24 2006, 11:18 PM

To quote Emily from her Planetary Society blog

"WOO HOO" ...... indeed!!!!!!!!!!!!!

But what will it take to confirm that what we see are indeed liquid lakes? Should we look for evaporation over time? What are the radiometric and scatterometry characteristics that could nail this down (are there any)?

Agree with Jason that these have the visible character of some of the calderas on Io.

How VERY COOL (pun intended)!!!!!!!!

Craig

Posted by: Rob Pinnegar Jul 24 2006, 11:31 PM

Okay. Let's assume that these are lakes.

There are a bunch of them near the north pole but not many at the south pole; just Ontario Lacus, which, last I heard, could just be mudflats at the present time. Making a further assumption that this isn't a coincidence, here's some wild speculation:

(1) Does this mean these lakes are seasonal? If they are seasonal, the northern-hemisphere lakes would have to start to evaporate as we get closer to ring-plane crossing -- *IF* sunlight at Saturn packs enough energy to evaporate the lakes (I have no idea whether this is possible).

(2) The methane would presumably have to transfer from the northern to the southern hemisphere. So will we perhaps see a "rainy season" starting as we get closer to 2009?

I guess that any seasonality of Titanian lakes could also involve groundwater (groundmethane?) flow -- maybe no rainy season required.

Don't know if there's anyone out there who specializes in both planetary science and hydrology, but, if so, they're gonna love this.

Posted by: belleraphon1 Jul 24 2006, 11:50 PM

Agree here with Rob...

Close up monitoring of the seasonal changes is paramount. Will methane follow the dark..... evaporate in the sun and unleash brief methane monsoons at the lower latitudes until a new
equilibirum is reached at the southern pole as it retreats into a winter darkness...... ??????

This really speaks to an extended CASSINI mission as a precursor to future Titan missions.

Craig

Posted by: Bjorn Jonsson Jul 25 2006, 12:26 AM

Now Titan is even more interesting than before, an extended mission even more important than before and as before, almost too many interesting targets to explore at Saturn. And probably at least 15-20 years until a new mission gets launched towards Saturn.

Will the northern lakes disappear and if so, when? Will lakes form near the south pole when it recedes into darkness and if so, when?

Hopefully Cassini lasts years beyond its primary mission, enabling it to observe seasonal changes (Titan and Saturn's blue northern hemisphere).

Posted by: Decepticon Jul 25 2006, 01:00 AM

Does this radar swath go over the north pole?

I'm not sure what area was imaged exactly.



As for those lake like features...... WOOOO HOOO!!

Posted by: AlexBlackwell Jul 25 2006, 01:23 AM

If by "confirm" you mean a point at which everyone unequivocally accepts a "liquid lakes" explanation for these particular RADAR data, then probably not until a probe actually lands in one, if then. In other words, I'm sure that up until that point there will be holdouts who will offer, for example, heuristic plausibility arguments positing alternative explanations.

Posted by: David Jul 25 2006, 01:25 AM

When they come into sunlight, could Cassini detect specular glints from them?

Also, have we seen features that could be dry lakes elsewhere on Titan?

Posted by: AlexBlackwell Jul 25 2006, 01:30 AM

Possibly, but it would depend on the geometry. At any rate, there should be data on the diffuse and specular components in the RADAR scatterometry data, which do not depend on solar illumination.

Posted by: volcanopele Jul 25 2006, 02:08 AM

Unfortunately, it is very difficult to search for specular glints in the polar regions. I think our farthest south data point is 53 S from Rev09 last June. We can search for specular glints using the altimeter, if we were to fly right over a lake, like during T38 (or T39, can never remember which) when we fly directly over Ontario Lacus.

BTW, there seems to be some confusion over the liquid state of Ontario Lacus. Ontario is a dark, footprint-shaped feature in the south polar region. The shape of the margin and its location in an area where clouds have been observed has led to the suggestion that it maybe a lacustrine feature. Based on data currently available, we can not tell if there are currently liquids in the lake or if it is a playa instead. Doesn't mean we know either way. It could be lake currently filled with liquids, it could be a mud flat. We don't know.

However, I think the picture is emerging that the lakes we see in RADAR were last filled with liquids last northern summer during the rainy season and that since the onset of winter in the region, these lakes are either evaporating or emptying into underground reservoirs. Some of these lakes reside in basins only partly filled with "liquid" (for the rest of this post, liquid stands in for RADAR-smooth material at high latitudes) with no apparent topography confining the location of the liquids into a subsection of the basin. Perhaps these lakes were filled in summer, and are now emptying thanks to the decade-long dry season. The antarctic lakes have now filled up from 5 years of monsoon rains, so it would be interesting to compare them to the arctic lakes when RADAR views them in T38 (or T39).

Posted by: volcanopele Jul 25 2006, 02:19 AM

Note: South is up in both cutouts in the release, and radar illumination from above.

Posted by: JRehling Jul 25 2006, 03:25 AM

I was in on that. If you are like me, you've thought about that bet over a hundred times since then. The poor fellow on the other side became mighty scarce (prematurely) after one of the first flybys (even before Huygens).

The bet's not over, but it looks good.

Posted by: JRehling Jul 25 2006, 03:37 AM

If attitude control propellent is truly the life-limiting factor for Cassini, then the variable in our control is the number of pointing operations (under current operational norms, the number of flyby observations) per unit time. Even if Titan were the only object under consideration, the choices would be, at the extremes, dozens of flybys at the current rate, obtaining more RADAR (especially) and VIMS coverage, but only lasting a couple of years (going just past equinox) or a more languid rate of coverage, making few observations (perhaps many "blind" flybys with few or no observations), but lasting well into the next Titanian seasons. Obviously, flybys of the other satellites would subtract from the Titan observations.

These lakes might relegate Iapetus, aside from its late-primary-mission closeup, to "see you next mission" status. Enceladus will still hold its own as an extended mission candidate, but the other icy moons are looking forgettable in comparison.

Posted by: qraal Jul 25 2006, 11:36 AM

Hi All

Lacustrine wannabes at last!

Hate to say it, but there's nothing as interesting as Titan and Enceladus amongst the rest. Titan we're more likely to learn much, much more about by an extended mission.

Has anyone looked into aerobraking Cassini into a survey orbit around Titan?

Adam

Posted by: Bjorn Jonsson Jul 25 2006, 11:38 AM

This has been discussed here before (I don't remember where) and it is not possible.

Posted by: JRehling Jul 25 2006, 11:45 AM

Quite a few, I'm sure. There are linear features in north of Tsegihi that I've always thought are (probably) dry versions of the Scottish lochs. In fact, they were among the very first features to show up in any Cassini images.

It's a reasonable conjecture that the entire darker equatorial region is a dry sea. In fact, it may be hard to explain unless it were at some point entirely submerged.

Posted by: David Jul 25 2006, 12:00 PM

Hm. On earth, lochs are glacial features. So are the scattered Minnesota-style lakes to which the Titanian lakes are being compared. But glaciation isn't possible on Titan -- is it?

Posted by: The Messenger Jul 25 2006, 01:35 PM

It's hard to figure how liquid methane would carve up a surface, especially since we are still very uncertain about what the surface is. Although it is unlikely, water-ice cannot be ruled out as the culprit.

Posted by: ljk4-1 Jul 25 2006, 01:53 PM

Has sulfur in any significant amounts been detected on Titan?

Or anything particulary corrosive? Or perhaps a substance that is
harmless by itself but becomes corrosive when combined with other
elements on Titan under its particular climate conditions?

Posted by: JRehling Jul 25 2006, 03:36 PM

Good point on the origin -- I was thinking of the structure alone. The features on Titan are probably tectonic, being parallel to the whole Fensal region.

Posted by: Olvegg Jul 25 2006, 05:08 PM

And what about translucency of luiqud for radar beam? Note that coastal areas of even darkest lakes (for example, one in the left up corner) are brighter, rather grey than black. It could be interpreted as sandbank, but also as shallow water (shallow methane? ), which doesn't absorb radar signal completely. The change of brightness is gradual, without contrast boundaries. All this would mean these lakes are quite deep!

Posted by: AlexBlackwell Jul 25 2006, 05:43 PM

This questions pops up so frequently on discussion boards that there should be an FAQ posted somewhere. I posted a http://www.unmannedspaceflight.com/index.php?s=&showtopic=1989&view=findpost&p=46972 in another thread on this issue. And as you note, the short answer is no, Cassini is not designed to aerobrake.

Posted by: AlexBlackwell Jul 25 2006, 06:15 PM

Yes, he should get his checkbook out

I seem to recall he mentioned that he was going offline to do graduate work for, I believe, David Stevenson at Caltech.

Posted by: Holder of the Two Leashes Jul 25 2006, 07:08 PM

Another slow loop out to Iapetus with a non demanding slow flyby is consistant with "a more languid" mission scenerio extending the time past equinox. Especially if you're not too tight in your targeting. but only want to get close enough, say ten to fifty thousand km, to complete coverage of areas previously missed. All of this, provided of course, that it's not too difficult to get into this orbit in the first place.

I'm still holding out for some kind of second Iapetus pass.

Posted by: Myran Jul 25 2006, 09:00 PM

When UMSF got so slow yesterday I wondered if something big was up with just too many visitors.
And im now wondering if this one might have caused it.
Its such a major find, another body in the solar system with liquid lakes on the surface.

Its mainstream
http://edition.cnn.com/2006/TECH/space/07/25/saturn.titan.ap/index.html now BTW.

Posted by: AlexBlackwell Jul 25 2006, 09:09 PM

Getting back to Iapetus during an extended mission would be nice, but as I http://www.unmannedspaceflight.com/index.php?s=&showtopic=1989&view=findpost&p=47169, doing so under most of the EM options being considered would require a lot of work and some not-so-minor sacrifice(s) of other, presumably more important, science objective(s).

Posted by: Holder of the Two Leashes Jul 25 2006, 09:37 PM

My hope is that somehow they can do detailed coverage of the "snowman" plus points to the east and southeast of there. Of course, I'll accept the fact that all this has to be incidental to additional coverage of Titan and Enceladus. I'm just hoping some mission planners are on the lookout for an opportunity to work in some additional Iapetus coverage on the side.

Wouldn't a few extra liters of propellant be nice right about now? Well, can't have everything.

Posted by: AlexBlackwell Jul 25 2006, 09:43 PM

It's doable, to be sure. And Cassini prop margins (which have always been conservatively estimated) are much better than predicted. If anything nixes a close Iapetus flyby during the EM, it'll probably be a competing faction(s) of scientists who wanted to do something else that precluded it.

Posted by: Matt Jul 25 2006, 10:07 PM

Just imagine what it would be like to be walking towards the shore, then look out over the hydrocarbon lake, with Saturn above.

We've seen plenty of artists renditions depicting such a scene....but now its reality!

Super!

Posted by: Stu Jul 25 2006, 10:19 PM

Yep, I can imagine that... it would be sooo beautiful... sadly, as I understand it, I think that from the lakes' altitude (i.e low) Titan's atmosphere would be far too dense and smoggy to allow you to see Saturn... Maybe if you climbed one of the mountains or (suspected) volcanic caldera you might. MIGHT just see a hint of Saturn through the clouds, but I wouldn't bet the Hab on it...

Posted by: AlexBlackwell Jul 25 2006, 10:22 PM

Maybe it's time for Ralph Lorenz to update his now-famous flying-and-swimming-on-Titan sequences in "http://shopping.discovery.com/product-15357.html."

Posted by: JRehling Jul 25 2006, 10:41 PM

In terms of Titanian skygazing, note that the ratio of sunshine (daytime) vs. saturnshine (selected nighttimes) would be much smaller than sunshine vs. moonlight ("moonshine"?!) on Earth. Something like ~6 magnitudes. It would probably be bright enough to read by saturnshine on a Titan night. However, that would probably take the form of an extremely diffuse light from the whole sky, or at least most of it. It would probably look like the view you get looking up at a cloudy sky in a city on Earth, with the clouds lit by the lights below (on Titan: haze lit from the Saturn above). It would be interesting to know if the light were in any way localized, ie, concentrated in the general part of the sky where Saturn was instead of just all over. I think it would be pretty well spread out. Now, if you had IR vision, you might see Saturn pretty distinctly as an object with fuzzy boundaries.

The polar regions of Titan would only have a side-looking view of Saturn, which would cut the light input quite a bit. So you'd have a nicer experience if there were a midlatitude lake.

Posted by: Thorsten Jul 28 2006, 08:25 AM

I’m a little puzzled by the latest News Release on the T16 RADAR swath:

http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=679

Cassini scientist are now quite confident that at least some of the radar dark spots are indeed lakes (which is great!). They further state that “the lakes are most likely the source of hydrocarbon smog in the frigid moon's atmosphere”.

I thought that the hydrocarbon smog was generally hypothesized to originiate from organic molecules formed by photodissociation of methane in Titan’s upper atmosphere. So do they presume that the hydrocarbon smog comes indirectly from methane evaporating from the polar lakes and thus replenishing Titan's methane atmosphere?
Are these comparatively small lakes really sufficient to replenish the atmospheric methane? At the northern hemisphere, they seem to be quite restricted the latitudes above 75 degrees. Furthermore, some of these “lakes” appear to be only partly wet at the moment and probably do not harbor large quantities of liquid methane.
Isn’t it still more likely that methane from Titan’s interior (released by cryovolcanoes, low temperature serpentinization, whatever) prevents the atmospheric methane depletion? At least, there is some circumstantial evidence for volcanic activity, like the detection of 40Ar by Huygens’ GCMS.

Posted by: ugordan Jul 28 2006, 09:04 AM

That statement caught my eye, too. I think that's stretching it a bit. The lakes contain methane which in turn evaporates into the atmosphere where it's broken down by UV light to produce smog. So technically, they are the source of the smog (not a direct source, though!). The wording is a bit awkward.

I agree with you on the point of lakes being just a temporary reservoir of methane, cryovolcanism is probably the mechanism by which Titan's methane is replenished. Without it, the lakes would eventually all dry up because all methane would be destroyed on a fairly short timescale.
That is, unless there's actually a vast reservoir of methane hiding below the surface. The question would then be: where'd THAT come from?

Posted by: tty Jul 28 2006, 10:33 AM

It may have been there since Titan formed. Like the old lady said "It's turtles all the way down"

tty

Posted by: volcanopele Aug 1 2006, 04:42 PM

I was kinda half joking Imagine my surprise when I checked my mailbox this morning...

Posted by: angel1801 Aug 8 2006, 02:55 PM

Just one simple question. When will we able to see the whole T16 SAR swath?

I know it started at about 53S latitude and almost reached the north pole of Titan.

And we have only seen the bits near the north pole!

Posted by: volcanopele Aug 8 2006, 02:59 PM

Best case scenario would probably be in October, either right before T19, the next major SAR pass, or in the second week of October for the DPS meeting (which I may or may not be at, it's still up in the air). The latest you would see the whole thing would be in early July of next year when it is released on to the PDS.

Posted by: JRehling Aug 8 2006, 05:51 PM

Did you get paid? I think I got a fully-fledged piece of the bet...

Posted by: Sunspot Aug 8 2006, 06:17 PM

Have you seen the whole radar swath? Anything else in it catch your eye or did they already release the interesting bits?

Posted by: volcanopele Aug 8 2006, 06:26 PM

Yep. I think I will frame the check instead, though, not sure yet.


Yes.

Posted by: Sunspot Aug 8 2006, 09:56 PM

........... to what? lol

Posted by: Big_Gazza Aug 9 2006, 02:59 AM

Has anyone estimated the illumination levels on Titans surface during day/night? Has the Huygens probe measured this directly?

Typically, for earth conditions, the following levels are typical:

Twilight - 4 lux
Full Moon - 0.2 lux
No Moon - 0.001 lux

Posted by: Thorsten Aug 9 2006, 06:19 AM

There is some information about daylight illumination levels on Titan’s surface in one of the Huygens’ Papers, released last December (Tomasko et al., 2005)

“The brightness of the surface of Titan is about a thousand times dimmer than full solar illumination on the Earth (or 500 times brighter than illumination by full moonlight). That is, the illumination level is about that experienced about 10 min after sunset on the Earth. The colour of the sky and the scene on Titan is rather orange due to the much greater attenuation of blue light by Titan's haze relative to red light. If the Sun is high in the sky, it is visible as a small, bright spot, ten times smaller than the solar disk seen from Earth, comparable in size and brightness to a car headlight seen from about 150 m away. The Sun casts sharp shadows, but of low contrast, because some 90% of the illumination comes from the sky. If the Sun is low in the sky, it is not visible.”

During the night, it will probably be quite dark at the Huygens Landing Site, since this place it on the anti-saturnian hemisphere of Titan.

Concerning the T16 RADAR Swath: I am also anxious to know if there are some really striking parts left to be released, but I guess patience is mandatory here.

Posted by: Bill Harris Aug 9 2006, 01:02 PM

I wonder how long twilight lasts on Titan? On Earth, astronimical twilight lasts for about 1.5 hours, or 22 degrees longitude. On Titan, I might expect twilight to last longer since the atmosphere is thicker and deeper (relative to the radius), but it may be "dimmer" since the atmosphere is more opaque.

--Bill

Posted by: JRehling Aug 9 2006, 03:10 PM

I'm surprised to see the progression/extent of twilight talked about as a singular thing. It surely varies with season, latitude, and sky conditions. At equinox on the equator, the Sun plunges perpendicularly to the horizon, dropping 15 degree per hour. At midlatitudes, it typically slices at a 45ish-degree angle, and so proceeds below the horizon at about 70% that rate. US/Europe travelers to the tropics may be shocked at how quickly sunset leads to darkness. Of course, in the polar long seasons, even when the Sun does set, it doesn't get very far below the horizon.

Even in "clear" weather, humidity and dust can soften/mute the light/dark distinction: humid air 15 km overhead can still "see" the Sun about 20 minutes after sunset, while the air over the western horizon roughly doubles that. But subtract the humidity and the effect becomes much less relevant.

In a nutshell, I think the residents of Oslo and Tuscon have a very different experience at twilight.

Posted by: Rob Pinnegar Aug 9 2006, 05:53 PM

More importantly, Titan turns on its axis only once every 16 days.

Posted by: ngunn Aug 10 2006, 09:57 AM

Bill's question is interesting. As he refers to degrees of longitude I'm sure he means how long is twilight as a fraction of the day length. Or (to eliminate the latitude issue) - How far below the horizon does the Sun have to be for complete darkness on Titan? I too would expect the answer to be greater than the corresponding value for Earth because the ratio of atmospheric scale height to radius is approximately 6 times greater for Titan. (For the very distended outer layers of Titan's atmosphere the scale height is 2.5 times greater still, but I'm not sure how much twilight this very tenuous part of the atmosphere would contribute.) In the case of an arbitrarily small small globe with a very extended atmsphere there would of course be twilight all 'night'.

Posted by: Matt Aug 27 2006, 10:30 AM

Anybody know anything about T17 yet?

It sounds like one of the closest flybys so far at 1,000 km.

Posted by: Thorsten Aug 31 2006, 11:57 AM

Apologies if this has been posted before, but there’s are quite recent (8/29/2006) CHARM presentation on Titan (http://saturn.jpl.nasa.gov/multimedia/products/pdfs/20060829_CHARM_Soderblom.pdf). What I found interesting is the plethora of question marks after the arctic “ethane/methane lakes” detected during T16 (see the last pages of the presentation). They have sound a lot more confident in the latest press release (http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=679).