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Posted by: remcook Aug 4 2005, 10:58 AM

..according to earth-based measurements

http://www.newscientist.com/article.ns?id=dn7786&feedId=space_rss20

The surface doesn't look like an ocean anyway

Posted by: TheChemist Aug 4 2005, 11:37 AM

Hello, we have an orbiter and a lander on Titan, hello

Posted by: alexiton Aug 4 2005, 12:31 PM

As kooky as I might sound, some people are in for a hell of a surprise regarding Titan. I could comment on New Scientist article, but suffice it to say, some scientific orthodoxies are destined to be utterly shattered - who wants to take a bet?

Posted by: TheChemist Aug 4 2005, 12:57 PM

Hello Dr. Porco, it's nice to know you post in these boards

Posted by: JRehling Aug 4 2005, 01:26 PM

I think the picture that we've seen is that the dark areas in the low latitudes (+/- 40 or so) have the shape of oceans -- but aren't. They are possibly pretty flat, dark, show signs of once having been an area where liquid flowed down from the brighter highlands, but now are either dry with dark organic sediments coloring things or are damp -- mud as Alex Blackwell has recently said.

The high latitudes (near the south pole, anyway) are a different story -- potentially. They may be just like the low-latitude dark areas, but we simply don't have confirmatory evidence one way or the other -- they could be unlike the low-latitude "dry oceans" and actually be lake/river/marsh even sea (the "Dinosaur" of T0) with wet stuff flowing now. One good reason to think so would be that that region is where there are actually clouds now. And the 938 nm view shows that Peanut as well as the Dinosaur and the channel systems down there seem a little more prominent. I think we're seeing what is at least seasonal liquid activity, and it'll turn out that Titan is another wet world, but covered with something more like 1% liquid in contrast to the Earth's 72%.

Posted by: volcanopele Aug 4 2005, 03:00 PM

In terms of looking for an IR specular reflection, the ground-based observations trump us so far. they have much better longitudinal coverage than we do. Unfortunately, they can only look at one latitude (that gradually changes with season), but they can still make far more measurements than we can. Still the picture that is emerging is of dark regions that may have once held liquid but don't now, or are only filled partially from rains. The polar regions may be filled with lakes seasonally.

Posted by: TheChemist Aug 4 2005, 03:24 PM

Thanks volcanopele !
I am not doubting the usefullness of earth-based studies, quite the contrary. I just thought liquid oceans on Titan were more or less excluded already based on Cassini/Huygens data. Let's find some lakes

Posted by: volcanopele Aug 4 2005, 03:54 PM

True, but we have looked in fewer places, but we have looked at a wider range of latitudes.

Posted by: Decepticon Aug 4 2005, 05:41 PM

I think they are jumping the gun here.


I'll wait till cassini is done.

Posted by: David Aug 4 2005, 05:48 PM

Supposing that the dark areas once held liquid but no longer do: where did it all go?

If there is little or no precipitation on Titan, why are there fresh-looking channels? Why aren't they gradually effaced, looking more like the ancient channels on Mars?

Why are there dark deposits only in the channels and below a sharply defined "shoreline", but not on the lighter-colored highlands? Wouldn't any precipitation that could leave deposits in the channels also leave deposits on the highlands as well?

Posted by: volcanopele Aug 4 2005, 06:32 PM

It is possible that the surface is porous and the methane drains into a methanifer. WRT the channels, we could be looking at an analog to deserts on earth, where rain is rare, but when it does rain, it usually leads to flash floods, causing just as much erosion as less water over a more sustained period of time.

My favorite theory right now, is that the dark regions, at least near the equator, represent dune seas, with lots of sand and lots of dunes/cat scratches. The get rain once in a great while, but it doesn't stick around for long, leaving behind mud flats.

Posted by: BruceMoomaw Aug 4 2005, 07:51 PM

The question "Where has all the liquid gone (long time passing)?" has two different aspects on Titan, because there are two different types of liquid. Methane, as we now know from Huygens, rains down periodically on the surface and then has the ability to re-evaporate back into the air.

But the very slowly built-up liquid ethane -- which we now know was also detected on the surface by Huygens, although they haven't publicly released quantity data yet -- will not evaporate once it forms, and calculations of its formation rate over the eons have long predicted enough for a global layer over a kilometer thick. So it must have soaked down into Titan's subsurface. I suspect much of it has been permanently carried down into Titan's deeper interior by its cryovolcanism and its resultant crustal recycling. A.D. Fortes has an interesting abstract at the upcoming DPS meeting on the possibility of "mud volcanism" on Titan: http://www.aas.org/publications/baas/v37n3/dps2005/126.htm .

By the way, we now have confirmation from http://www.aas.org/publications/baas/v37n3/dps2005/31.htm that Huygens not only detected ethane from the surface when it was heated, but also cyanogen and -- really surprisingly -- carbon dioxide. (The first two were mentioned briefly by the Solar System Strategic Roadmap.)

Posted by: remcook Aug 7 2005, 10:19 AM

Well, CO2 does condense at the tropopause, although it is not very abundant in the stratosphere (but more so than water). So there should be some ice at the surface, maybe not in the quantities observed, I don't know.

Allow me to hop on the cryovolcano bandwagon for a moment and speculate a bit:
a cryovolcano would mostly produce CH4, CO and H2O (is this right?). CO and H2O can recombine to form CO2 if H2O gets dissociated. Not sure how this could be low in the atmosphere...
But maybe a volcano could produce CO2 directly as well. ????
Honestly, I don't know. Does anyone have more info on what a cryovolcano on Titan is supposed to do?

Posted by: Bob Shaw Aug 7 2005, 05:48 PM

I think that's right on the button!