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Posted by: Webscientist Jul 23 2006, 02:06 PM

The Cassini radar images taken during the flyby of April 30, 2006 show the bright Xanadu region. One big surprise is that it is made of highlands and mountains more than 1000 meters high ( 0.62 mile ). It contradicts the expectations of most scientists who thought that mountains didn't exceed 300 meters.

And the radar images indicate that the constituent of those mountains is similar to a porous water ice. So imagine a giant mountain made of water ice!

The Xanadu region also shows networks of drainage channels. They appear bright in the radar images. How to interpret? normally, a liquid should be less reflective!

http://www.titanexploration.com

Posted by: Phil Stooke Jul 23 2006, 02:27 PM

"The Xanadu region also shows networks of drainage channels. They appear bright in the radar images. How to interpret? normally, a liquid should be less reflective! "

Debris on the floor of a dry channel, not liquid flowing in a channel.

Phil

Posted by: Richard Trigaux Jul 23 2006, 07:08 PM

1000m???

this makes a lot, for a crust which is supposed to be formed of water ice. Water ice flows slowly, so that any mountain (or hollow) is cancelled. So the explanations could be:

-there is a dynamic process keeping these mountains up (as on Earth, where high mountains remain high because there are tectonic forces raisin them).

-water ice is not the main constituent of the crust, at least not the upper layer.

-these mountains are floating on something (like Earth's continents). But what is floating on what? Water ice cannot float on hydrocarbons. But ammonia entectic may float on water ice. Eventually cryovolcanoes, or tectonic processes, would bring up ammonia eutectics on the surface, where ot would slowly lose its ammonia (was ammonia detected in Titan air? it would be a signature of recent volcanism, as ammonia would decay rapidly into nitrogen and hydrogen)

Funny too is the rubble structure of these mountains. There is no equivalent of this nowhere else. Possible explanations:
-meteorite ejecta
-these blocks once floated on an ocean
-a peculiar differential erosion process would work

Posted by: JRehling Jul 23 2006, 11:38 PM

Is that it? My thought was that the side-looking radar was showing the far side of a channel (low angle of incidence) bright and the near side dark. I guess it would have to be a very sharply delineated channel to do that... but that's what we saw in a lot of Magellan images, or so I thought.

Posted by: Phil Stooke Jul 24 2006, 01:54 AM

Webscientist originally said "a liquid should be less reflective!" My comment was intended to mean - "it's not liquid". It may be that the debris is talus on the slope of the valley, not alluvium on the floor, but that's not really what I was getting at.

But I could have chosen my words more carefully.

Phil

Posted by: Richard Trigaux Jul 24 2006, 06:04 AM

downloading the entire radar swap (60Mo) is worth waiting, there are plenty of details on it.


I noted some facts:

-mountains don't seem eroded by rain, ther e is no valley-crest pattern.
-however there are long drainage channels, very earth looking, like rivers and river branching.

This is not coherent: on Earth, both go together. Rain creates rivers, and it erodes mountains in a recognizable way.


Another contradiction:
drainage channels goes in clear zones and dark zones as well. Some even go through dark zones, then into clear zones, and back in dark zones. This is not coherent if we assume that darl zones are low and clear zones are high. The only coherent thing is that mountains are clear, and flow channels go around, not through.


Also on Earth there are rivers everywhere (and even river beds in very dry zones). Especially we find rivers radiating off mountains and gathering into low lands, following tectonic slopes and bottoms. On Titan there are just some large river beds spread at random throught dark or clear areas.


So I think that the liquids play a fundamentaly different role on Titan than on Earth. Already some on this forum theoretized that methane rains would be violent, but very rare. On Earth this gives desertic land forms, with very large wadis and alluvion fans all around the mountains, that we comonly see into Sahara, Saud Arabia, etc. Nothing such on Titan. Rains would be so rare that to have fell into only some places in tens of million years? Are there really rains at all? And if not, where the liquid comes from and where it goes, to form such drainage channels?

What is funny too is that the drainage channels are large, like large flows. They show meanders in some places. But these meanders show little evolution, as if the flow was of only a short duration. But this short duration flow however deeply gouged into the land. So there must be a special erosion form, not just mechanical as in Earth rivers. For instance a surge of hot water (from underground) cutting into water ice or hydrocarbons, or methane dissolving other hydrocarbons.

The only familiar feature I see is those potato-shaped darker areas we see in many places into the clear lands. They look very much like what we see in Sahara, where rain gathers into hollow places. Those hollow places are then outlined with dry vegetation, so that they appear as stains. On Titan the hydrocarbons falling from the sky would play the role of the vegetation, outlining the hollow places. But if so, the dark lands are much darker...

Interesting indeed.

I hope I shall see one day a Titan flyer getting all these places analyzed, and answer all these riddles. I remember that, when I was a kid, Titan was a mere spot of light...

And if it is true that we survive after death into a spirit body, I shall certainly use it to visit Titan.

Posted by: tty Jul 24 2006, 06:28 AM

So what's so strange about that? I've seen taller ice-mountains than that here on Earth. They're known as "ice-caps" or "glaciers". Admittedly they are rather flat since ice flows plastically, but at Titan temperatures ice would be much stiffer and the gravity is lower.

Perhaps the best analog on Earth would rather be Mount Sedom southwest of the Dead Sea. This is a sizable (and rugged) mountain of rock-salt, a substance which also flows plastically but much slower than ice. It is unique as far as I know since almost anywhere else a salt mountain would melt away much faster than it could form.
There maybe another parallell with the porous Titanian mountains, since even the very rare rains in the Arava valley are sufficient to create cave systems in the salt ("halokarst").

tty

Posted by: David Jul 24 2006, 06:34 AM

There may be many, many smaller streams that are not visible at this scale, however. None of the streams imaged by Huygens was big enough to show up on radar. The huge rivers may be quite rare, but the smaller ones could be ubiquitous for all we know.

Posted by: Richard Trigaux Jul 24 2006, 06:37 AM

If so, they would be hidden by the granulous nature of the radar images.

Posted by: Big_Gazza Jul 24 2006, 11:08 AM

I have mused on this during the odd lucid moment, and while it is certainly a low cost and potentially long term exploration concept, the difficulty of transmitting data back to ones earth-bound fraternity will probably prevent soul-travel from being a practical option.

When my time comes however, I will add Titan to my list of must-see after-death destinations. Europas' oceans come first, then Io's volcanos. I quite fancy a leisurely stroll (or float) over the smouldering surface of the caldera of Tvashtar Catena.

Anyone else have some hot tips? C'mon, I sure everyone has a favorite....

Posted by: MarcF Jul 24 2006, 06:27 PM

The radar SAR data indeed seem to show mountains, but are they confirmed by some altimetric data ?
1000 m high structures should be easy to confirm.
I did not find any altimetry since the first Titan flyby.
I'm also thinking about this big "rain-washed" continent :
Could Xanadu be a Titanian equivalent of the Tharsis bulge on Mars ?

MarcF

Posted by: JRehling Jul 24 2006, 06:35 PM

In 1981 or so, my grandmother and I made an agreement to meet there upon my passing. Way before Cassini!

Posted by: volcanopele Jul 24 2006, 06:40 PM

The RADAR team used radarclinometry to estimate slopes seen in the SAR view. If you can estimate the slope, and know the length of the slope, you can get the height. Of course, you have to assume that every thing else is equal for this to work but you can get in the right ball part with depth and height.

This also works best over short distances. Over longer distances, some of the assumptions, like aconstant dielectric or volume scattering properties, may not fit. So altimetry is much better for understanding broad scale topography (like finding out if Xanadu is a plateau whereas the dune seas are lowlands (or vice versa), while radarclinometry can get you the height of a mountain or the depth of a crater or caldera.

Posted by: Richard Trigaux Jul 24 2006, 07:37 PM

That is, we are many. So we must ask Doug to make an after death UMSF to discuss our findings. Or rather Un Material Space Floating.

Posted by: MarcF Jul 24 2006, 07:49 PM

Thanks a lot, volcanopele.
Your explanations are always very clear.

Sorry for my ignorance in the field.
I'm expecting from Cassini far more than possible and it's so frustrating to have ever more questions but just few answers. As a scientist (in molecular biology and genetics) I should be used to !!!