[X] My Assistant

[Floyd]

Great Titan images down today. Lakes and the Belet region centered on about 270 degrees.

[Juramike]

How much liquid methane could the Equatorial Dune seas contain and still be relatively dry on top?

I had a little fun in the lab today. I took many common organic resin materials as a model for the polymer coated dunes of Titan. I then added heptanes as a model for methane to see how much hydrocarbon solvent could be accommodated in the pores and surface structure of the materials. [Polystyrene has minimal absorption of hydrocarbon solvents like heptane, solvents such as DMF and THF is a different story – they swell appreciably. DOWEX resins are polar ion exchange resins and are usually wet].

These were chromatographic supports and were fairly uniform (approx 100 – 200 mesh), meaning really fine. “Real” dune material is probably a whole variety of sizes.

I made a slurry with a known volume of heptane, then decanted the heptane phase until the slurry no longer flowed freely.

Here are the results volume solvent held (mL) in volume material (mL):

Chloromethyl polystyrene (Rapp polymere) 3.8 mL heptane held in 8.0 mL material
YMC C18 Reverse phase packing material 5.5 mL heptane held in 8.8 mL material
Sephadex LH-20 (25 uM-100 uM) 2.8 mL heptane held in 6.5 mL material
DOWEX AG-50W-X2 resin (+H2O) 3.0 mL heptane held in 7.1 mL material
DOWEX 1X2-100 resin (+H2O) 2.2 mL heptane held in 5.2 mL material
Sand (as sold by Fischer Scientific) 1.2 mL heptane held in 1.6 mL material


Chloromethyl polystyrene: 0.475 mL hydrocarbon solvent held/mL material
YMC C18 packing material: 0.625 mL hydrocarbon solvent held/mL material
Sephadex LH-20 0.430 mL hydrocarbon solvent held/mL material
DOWEX AG-50W-X2 0.422 mL hydrocarbon solvent held/mL material
DOWEX 1X2-100 resin 0.423 mL hydrocarbon solvent held/mL material
Sand 0.75 mL hydrocarbon solvent held/mL material

From all this, I’d be comfortable assuming an average value of 0.5 mL heptane held/mL organic material.

Extending to Titan, I’d estimate that 0.5 mL methane held / mL organic dune sand.

From a previous post (http://www.unmannedspaceflight.com/index.php?s=&showtopic=3698&view=findpost&p=86735), I estimated that the Equatorial Dune Seas volume is or 8.3 x 10^5 km^3.

Assuming all is available as a slurry reservoir for liquid, we get:

8.3x10^5 km^3 x [1x10^10^12 cm^3/km^3] = 8.3 x 10^17 cm^3 Equatorial Sand Seas volume in cm^3 (= mL).

Assume 0.5 cm^3 liquid methane / cm^3 equatorial dune material:

8.3 x 10^17 cm^3 dune material x 0.5 cm^3 liquid methane = 4.2 x 10 ^17 cm^3 methane held in equatorial sand seas.

Assume density of liquid methane at 94 K = 0.7 g/cm^3:

4.2 x 10 ^17 cm^3 methane held x 0.7 g/cm^3 methane = 2.9 x 10^17 g methane held

Which equals 2.9 x 10^14 kg methane potentially held in the Equatorial Sand Seas.

This is only 0.04% of the amount estimated in the Titanian atmosphere (6.5 x 10^17 kg).

So from this estimation, the Equatorial Sand Seas of Titan could be chock full of methane lurking just under the relatively dry surface and it still would not be a significant reservoir (0.04%!) of atmospheric methane.


[Juramike cerebral cortex officially blown.…]

-Mike

(Can anyone cofirm the 6.5 x 10^17 kg atmospheric methane value?)

[rlorenz]

Sounds like a lot of fun..... though I am not sure whether the dunefields have
been seriously considered as a methane reservoir, after all the sand had to
have been dry when it was blown around....

I had some fun myself a few weeks ago in Roger Clark's lab at the USGS in
Denver, poking around at the mechanical properties of materials at liquid
nitrogen temperatures.... one of the few precious occasions these days when I
got to do actual science..... we figured out where acetonitrile is on the Mohs scale.....

Anyway, your atmospheric methane number is pretty close, maybe a factor of 2 high

Pressure = 1.5 bar = 1.5E5 Pa, in 1.35 ms-2 gravity means about 1E5 kg/m2 column
mass (roughly 10x Earth - think of it as 7m of mercury...)
About 4% of that is methane (mole fraction 2% in the stratosphere, about 5% at surface -
weight by the latter number since that's where most of the atmosphere is)
so we have 4E3 kg/m2 of methane in the atmosphere - 4 tons per square meter, about
the depth equivalent of 10m of methane liquid. Compare this with the 20cm or so depth
equivalent of water vapor on Earth - a couple of month's worth of rainfall. Titan's
massive inventory is perhaps a millenium's worth of evaporation/rainfall.)

Anyway, 4E3kg/m2 .... Titan's surface area is 81 million km2 - 8E7 km2 = 8E13 m2
multiplying gives 3E17kg

Cross fingers for T28 tomorrow - should have some nice radar of dunes and seas....

Ralph

How much liquid methane could the Equatorial Dune seas contain and still be relatively dry on top?

I had a little fun in the lab today.
<snip >

(Can anyone cofirm the 6.5 x 10^17 kg atmospheric methane value?)

[tty]

..... we figured out where acetonitrile is on the Mohs scale.....

Incidentally, where is ice on the Mohs scale at that temperature?

[ngunn]

The latest news release on T28 mentions that the RADAR swath has been moved a bit south to catch the "other side boundary of the 'black sea'" rather than repeating coverage of the part with the island as described in the mission description.

http://saturn.jpl.nasa.gov/news/events/tit...70410/index.cfm

http://saturn.jpl.nasa.gov/home/index.cfm

[volcanopele]

??? I thought they were doing that for one of the May RADAR swaths?

[Juramike]

ARRRRRRGH! Thanks for the numbers, Dr. Lorenz! I knew I'd messed up the math in both posts! <insert "D'oh" emoticon here>

[For the record: 1 km3 = 1E15 cm3]

Recalculating for clathrate reservoir of methane the Equatorial Sand Seas: 1.28E15 kg methane could be held in a clathrate structure. This is roughly 0.4% of Titan's atmospheric methane.


For the "wet sand" idea, the hypothesis is that methane lurks just below the surface of the Equatorial Sand Seas: the lower part is wet methane saturated sand, but the upper section contains dry material blowing around and forming dunes - just like at the beach.

Here is the corrected estimate for methane in the Equatorial Sand Seas:

Equatorial Sand Seas area (10% of total Titan surface): 8E6 km2 = 8E12 m2
Assume 100 m average depth: 8E12 m2 x 100 m = 8E14 m3 Equatorial Sand Seas volume

Assume 0.5 m3 liquid methane/m3 equatorial sand material.

8E14 m3 x 0.5 m3 = 4E14 m3 liquid methane held in Equatorial Sand Seas material.

(Still assuming density of liquid methane at 94 K = 0.6 kg/1E-3 m3)

4E14 m3 liquid methane x 0.6 kg/1E-3 m3 = 2.4E17 kg liquid methane potentially held in Equatorial Sand Seas material.

2.4E17 kg methane potentially held under the Equatorial Sand Seas is close to the total amount of atmospheric methane (3.2E17 kg).


Figured another way:
4E3 kg/m2 methane/surface area x 1E-3 m3/0.6 kg = 6.6 m3 methane/m2 surface area (= 7 m deep in liquid methane all over Titan, which is close to 10 m methane as posted by Dr. Lorenz).

Shove all of this onto only 10% of the surface, and you would get a column of 70 m of liquid methane in the Equatorial Sand Seas. Assuming 50% holding capacity for the material, and you would need an average depth of 140 m in the Sand Seas to hold all of this liquid.


So, the area under the Equatorial Sand Seas could serve as an appreciable reservoir of liquid methane.

-Mike

[ngunn]

??? I thought they were doing that for one of the May RADAR swaths?

Well, which is the reason and which is the consequence? I don't know, but it sounds like many factors may have been weighed up for science reasons but mapping the shore of that 'sea' is the one for the press headlines. Heck, If you don't know - why am I even bothering to speculate??? I'm glad anyhow. It's good to see the team reacting that fast to incoming information.

[volcanopele]

I knew that the RADAR team had adjusted one of their RADAR SAR swaths to cover the middle and lower portion of the Caspian Sea. Basically, the RADAR team can choose between looking left or looking right when selecting a swath for SAR. For this flyby, they had chosen to look left, which would have given them repeat coverage with T25, as I wrote in the Looking Ahead article for this orbit. But it seems that the flyby they changed was this one, choosing to look right instead. I thought they had changed one of the ones in May, but now that I think about it, this makes sense. The only RADAR C/A coverage in May is T30 and that was changed, IIRC, to a full altimetry swath.

[Stu]

Cobbled this together from a couple of images taken during T28... channels? canals?

[Stu]

Slightly better...

[volcanopele]

who knows anymore They look a lot like Shiwanni Virgae (the streaky stuff south of Aztlan). Shiwanni turned out to be a mix of mountain chains and shallow depression. Unfortunately, shallow sedimentary basins and mountains look the same in near-IR images

[Juramike]

How long would it take to silt up the Equatorial Sand Sea volume?

Here are some North American rivers and their sediment loads.
(very cool website for flow data: http://www.grdc.sr.unh.edu/html/station.html)
(useful website for sediment load: http://co.water.ugsg.gove/sediment/conc.frame.html)

River; Mean streamflow (m3/s); Average sediment discharge (ton/yr); Average sediment discharge (kg/s), Sediment load (kg/m3 flow)

[EDIT: I meant this to be a really cool-o table, but I just could get the formatting. Sorry!]

Mississippi (LA) 17,600; 230; 6,440; 0.36
Copper (AK) 1,607; 80; 2,240; 1.39
Brazos (TX) 199; 11; 308; 1.54
Columbia (WA-OR)
pre-Mt. St. Helens) 5,438; 10; 280; 0.05
Columbia (WA-OR)
post-Mt. St. Helens) 5,438; 40; 1,120; 0.20
Rio Grande (TX) 115; 0.8; 22.4; 0.19
Colorado (CA-AZ) 21; 0.1; 2.8; 0.13
Pee Dee (SC) 283; 0.6; 16.8; 0.06


Assuming that Titanian rivers have a sediment load of 0.2 kg/m3. From the Table above this puts it between the cascading glacial milk of the Copper River and tannin-stained blackwater of the gently flowing Pee Dee River.

From the Jaumann et al. LPSC 38 (2007) abstract “Surface Erosion on Titan”. Two streamflows estimated on Titan during “rain events” are, according to their model:

Huygens area river mean discharge estimate: 900 m3/s
Pacman Bay river mean discharge estimates: 8600 m3/s

This puts the Pacman Bay discharge on the same order of magnitude as the Columbia River.

If we assume that Earth silt is 10x denser than Titanian silt (which is probably ice-based) we get a discharge load of 0.2 kg/m3 x 0.1 = 0.02 kg/m3.

0.02 kg ice = 20 cm3 ice = 20 mL

20 cm3 x 1 m3/1E6 cm3 = 20 E-6 m3 ice silt/m3 river flow.

If we assume that there are 100 rivers (I’ll bet this is vastly underestimated) of the same discharge rate as the Pacman Bay river dumping into the Equatorial Sand Seas basins, then we get:

100 rivers x 8600 m3/s river flow x 20 E-6 m3 ice silt/m3 river flow = 17.2 m3 ice silt/s dumping into the Equatorial Sand Seas when the rivers are flowing.

When would the rivers flow? Assume that there is a one time Saturn-yearly monsoon that lasts one day (24 h) [Is there a Titanian equivalent of a Milankovitch cycle?]

24 h/day monsoon x 60 min/h x 60 s/min x 17.2 m3/s = 35.6E6 m3/monsoon day.

35.6E6 m3/monsoon day x 1 monsoon day/29.5 years = 1.2E6 m3 ice silt deposited/year.


To fill up the Equatorial Sand Seas volume (estimated at 8E14 m3) with ice-silt, it would take 6.7E8 years. So a billion years of a once-Saturn-yearly deluge would do the trick.

So it is possible that the Equatorial Sand Seas are silted-up oceans.

-Mike

[tty]

35.6E6 m3/monsoon day x 1 monsoon day/29.5 years = 1.2E6 m3 ice silt deposited/year.
To fill up the Equatorial Sand Seas volume (estimated at 8E14 m3) with ice-silt, it would take 6.7E8 years. So a billion years of a once-Saturn-yearly deluge would do the trick.

So it is possible that the Equatorial Sand Seas are silted-up oceans.

Question: So how come Earth still has oceans after at least 3,5E9 years of rain and river erosion?

Answer: The silt is carried back and scraped off on the continental edges by plate tectonics.

Corollary: If the equatorial sand-seas are silted-up oceans, then Titan doesn't have plate tectonics.

[Littlebit]

Question: So how come Earth still has oceans after at least 3,5E9 years of rain and river erosion?

Answer: The silt is carried back and scraped off on the continental edges by plate tectonics.

Corollary: If the equatorial sand-seas are silted-up oceans, then Titan doesn't have plate tectonics.

...So how deep is the sand on Mars? How important was/is water in composition of the Martian dust? Was there ever tectonic activity on Mars?