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PostPosted: Tue Dec 23, 2008 12:12 am 
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EDG wrote:

The bottom is 80 to 100km down - any topography there wouldn't affect the surface at all, it's just not high enough to affect the wave motion. But most likely it'd be pretty flat down there on the ice surface due to the pressures.


No, I meant that there is absolutely nothing but water for 80 - 100km - the ocean would be about as thick as Earth's entire atmosphere!


OK, I will buy that (for a $1). Sorry that I missed that the depth was that thick.

Speculation here:
What would to the planet if an asteroid did impact?
Or say a spaceship the size of Traveller's AHL?

I can imagine that the ship without all its power put into its gravity systems would loose all integerty and look like squashed newspaper after only reaching say 10K depth (maybe sooner).
And it loose below that depth no matter what type of antigravity systems it might have.

Dave Chase

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PostPosted: Tue Dec 23, 2008 10:43 am 
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Quote:
What would to the planet if an asteroid did impact?
One helluva big *splash*.....

....I'll shut up now, shall I?...... :oops: :lol: :D


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PostPosted: Tue Dec 23, 2008 11:18 am 
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EDG wrote:
Yeah, the idea is that all the water is coming from ice-rich planetesimals that would usually have been incorporated into gas giants. In most cases these worlds would have formed at the inner edge of the Outer Zone and then migrated inwards a bit, so they're very stunted gas giants - if they'd remained in the outer system then they most likely would have become GGs themselves.

Hmm, so when GGs migrate inwards and get hotter or the star gets hotter over its lifetime (ala Sol), can the innermost GGs lose their H/He atmosphere and become Panthalassics?

Is there anything to be concerned about with solar tides (I am aware deep water tides are usually quite small) perhaps more at crust level/heating effects or with off-axis tides and spin oblateness?

Can a Panthalassic ever be solar tide-locked? (looks like it would take too long with a large planet) That might be interesting.

Quote:
There'd only be floating vegetation if something like that evolved there or was imported, and there's no solid surface at all (unless it happens to be cold enough at the poles for ice to form). And with the nearest solid surface about 80-100 km below the sea surface, you'd need a pretty long anchor :).

Yes, it would have to have some form of station keeping thrusters. I am leaning more to having a submerged base/city with multiple very large towers popping up above the waves, but which can all be totally submerged if it gets rough.

Considering what industries could form on the surface of such a world; Is there any industry that benefits from readily available high pressure sources? (put it on a cable and lower it in the ocean). Perhaps making icebergs to order (possibly a form of Pykrete http://en.wikipedia.org/wiki/Pykrete using local vegetation) to create usable land? Atmosphere/water extraction products? Seafood (and perhaps tourism in Space opera settings).


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PostPosted: Tue Dec 23, 2008 4:27 pm 
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Dave Chase wrote:
What would to the planet if an asteroid did impact?


Depends how big the asteroid was. In practical terms it won't really matter whether it hits land or sea - but with an ocean impact you'd get a lot of vaporised water blasted into the atmosphere (and possibly into space if it's a big enough impact), you'd get an instantaneous crater formed in the ocean surface which then immediately gets filled up by the surrounding water, shockwaves rushing around the planet until they run out of energy, etc. I think impacts would most likely be the primary way for the ocean would get more salts and impurities though, so over time it would add up. It'd be the same as an ocean impact on Earth, but without hitting the crust below.

Quote:
Or say a spaceship the size of Traveller's AHL?


Most likely the ship would break up in the atmosphere if it's coming in uncontrolled. It'd be just like a small asteroid, the thick atmosphere would serve as a barrier that destroys the small bodies in the air before they hit the ground.

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PostPosted: Tue Dec 23, 2008 4:32 pm 
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John B Stone wrote:
Hmm, so when GGs migrate inwards and get hotter or the star gets hotter over its lifetime (ala Sol), can the innermost GGs lose their H/He atmosphere and become Panthalassics?


It'd be hard, there's a lot of gas to lose and the temperature would have to get really high - Jupiter wouldn't lose its atmosphere even if it was 0.01 AU from Sol.

Quote:
Is there anything to be concerned about with solar tides (I am aware deep water tides are usually quite small) perhaps more at crust level/heating effects or with off-axis tides and spin oblateness?

Can a Panthalassic ever be solar tide-locked? (looks like it would take too long with a large planet) That might be interesting.


Solar tides usually wouldn't be an issue - in most cases the panth would be too far away. But if you could get them around M or K V stars then it'd be likely - larger planets actually despin due to solar tides more rapidly so you probably would get tidelocked ocean worlds. In which case you'd have some interesting current flows, and also even the dark side would probably still be liquid because of the heat trapped in the ocean.

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PostPosted: Tue Dec 23, 2008 11:48 pm 
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Funnily enough, an article on space.com that discusses potentially habitable worlds mentions these panthalassics too:
http://www.space.com/scienceastronomy/0 ... ories.html

Here's the relevant bit (though I disagree that they'd all be made completely out of water - maybe the smallest ones will but a proper panthalassic will have a rocky core. It'd be hard to accrete just ices without any rock, and the rock would settle to the core anyway):

Quote:
Water-worlds

The fourth kind of habitable planets are made almost entirely of water. These hypothetical worlds would be Mercury to Earth-sized and would feature extensive oceans. Unlike oceans on Earth, the water on these types of planets would not be in contact with silicates or other rocks.

"These planets can either be completely made of water with high pressure ice at the core, or they can have bodies of liquid water that are separated from a silicate core by a thick layer of high pressure ice," said Bredehöft.

One theory for life's origin on Earth says organic material collected in shallow pools and then became concentrated by clinging to the surface of rocks. Eventually, this early life spread into the wider ocean. Another theory for life's origin is that the necessary chemistry occurred at hydrothermal volcanic vents. On water worlds, however, these scenarios are impossible. Therefore, Bredehöft thinks life is not likely to originate on such planets.

"The amount of water on such a planet would be so huge, you would need unbelievable amounts of carbon components concentrated together for a chance of life. It's far too diluted," said Bredehöft.

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PostPosted: Thu Dec 25, 2008 5:38 pm 
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More pretty pictures for Christmas! :)

Here's another possible panthalassic - this time there's no ice X, so the pressure at the base of the ice VII layer doesn't have to be quite so high. This means the ice VII layer is thinner, and the rocky/metal body has to be bigger to compensate - in this particular model, the actual rocky surface has a radius of 8111.14 km, making that part alone about 1.3 times larger than Earth (and it still has another ~1350km of ice and water on top of it!). This model also has an inner and outer metallic core, which is somewhat more realistic than the other model I showed. Scale on the image is the same as before. The grey layer is the ice VII, the really thin white layer above that is the ice VI, and the thin blue layer above that is the (93 km thick) surface ocean. The planet itself has a total mass of 3 earth masses.

Attachment:
File comment: 6-layer panthalassic with inner and outer core, no ice X.
panth2.jpg
panth2.jpg [ 153.15 KiB | Viewed 1097 times ]


Code:
Layer  5 uncompressed density = 5150.00 kg/m^3
Layer  4 uncompressed density = 4300.00 kg/m^3
          layer %s:      0.70     0.30    15.00    65.00    15.00     4.00
     top densities:   1100.00  1422.83  1800.71  5095.74  8774.48 13774.02
    base densities:   1298.90  1456.99  2754.60  7260.13  9584.12 14324.14
       thicknesses:     93.09    34.05  1212.46  3757.87  2049.07  2304.20
brine     iceVI     iceVII    rock      FeS       Fe       
 base pressure/GPa:      1.52     2.19    43.28   369.02   562.68   718.90
 model radius  =  9450.75 km     cf. observed 10000.00
 model density =  5068.90 kg/m^3 cf. observed  5000.00
 model C/MR^2  =  0.319463       cf. observed  0.300000
 model gravity = 13.38940 m/s^2  cf. observed  9.80665

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PostPosted: Wed Jan 28, 2009 8:32 pm 
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So this is all on hold for a bit while I sort out and update my stellar evolution grids. But now I've got the density data for the big worlds I can figure out a way to get that in the program when I get back to it. .

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PostPosted: Wed Jan 20, 2010 5:48 pm 
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EDG wrote:
Dietrich hault-Rauln wrote:
Are you a JTAS Online subscriber? It so happens that I wrote a couple of articles on exactly that subject there...


Are you able to publish these articles yourself? I'd love to see them, but I'm not all that interested in spending $20 to join JTAS.

Frank


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PostPosted: Wed Jan 20, 2010 7:24 pm 
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ffilz wrote:
EDG wrote:
Dietrich hault-Rauln wrote:
Are you a JTAS Online subscriber? It so happens that I wrote a couple of articles on exactly that subject there...


Are you able to publish these articles yourself? I'd love to see them, but I'm not all that interested in spending $20 to join JTAS.


I wish. Unfortunately I can't publish them myself, and despite asking SJG several times over the years if they're ever going to to something sensible like actually allow people to buy articles individually, there's been no movement on that front. It's really annoying. :(

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