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PostPosted: Mon Dec 22, 2008 4:20 am 
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John B Stone wrote:
Do we have any idea what the effect of volcanoes would be on such a deep ice crust? Are volcanoes more or less likely with all that pressure? Is there scope for mega circulation currents from ice bottom to ocean top over geological hot spots?


Interesting question, and one I pondered during PhD (in the context of Ganymede, which has a similar structure to the panthalassics but is much smaller) :). The thing about pressure is that (a) high pressure will keep any gases in the magma dissolved in it - which basically means it can't be an explosive eruption - and (b) it makes it that much harder for the rising magma to force the rock open and force its way to the rock surface because the stresses have to be a LOT higher.

TBH I'm not sure what the combined effect of that is - most likely I think it means that you'd have fewer eruptions across the rocky body, but if they do break through they'd be localised fissure eruptions that just spread out over the rocky surface. Though you'd have ice right on top of it, so that could melt the ice at the base... though the weird thing about ice X is that even at 1000K it won't melt! Basically, I have no clue what would happen under the conditions we're talking about here. In practical terms nobody would be able to get down there to take a look though. At best I'd say that maybe you could get convection happening in the ice layer, but that's about it.

As an aside, the ocean is probably going to be warm throughout - I think the only reason that the bottom of Earth's oceans is so cold (a uniform 4°C) is because of all the polar water that's sinking to the bottom and not warming up. If the planet is warm though - as is likely to be the case here - then the bottom of the ocean could be pretty warm too (in practical terms, a colder ocean floor would allow for a slightly thicker ice VI layer, but that's about it. The ice VI itself can be stable up to about 80°C though at the pressure's we're talking about).


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Considering the massive amount of water needed for Panthalassic worlds compared to inner planets in our solar system - I assume all this water in our system has ended up in Gas Giants?


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.


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I am trying to visualize what surface installations would look like on this thing or if there would be any surface features like floating vegetation mats or "forests". Maybe floating towers - a variation on the proposed floating wind turbines.


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 :).


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Presumably all non-organic building materials would have to be brought from off world? Even scavenging for meteor debris on the sea floor looks too hard.


Yeah, minerals that couldn't somehow be extracted from the seawater would be hard to find (and I'm not even sure it'd be THAT salty... there'd be no runoff from continents adding to the water, and nothing from a rocky seafloor... so the only input would be the original saltiness of the volatiles that formed the ocean, and any subsequent impacts. Meteors and many small asteroids would be largely disintegrated in the thick atmosphere too, and any bigger asteroids would just vaporize the ocean at the impact site the same as they would if they were hitting land. But still, it'd be a way for minerals to get into the system, and some bits may settle to the sea floor. So if the technology allows for at least robotic mining subs to trawl the seafloor looking for meteorite fragments (similar to how people find them on the ice of Antarctica - they stand out somewhat from the ice!) then it could be possible - but they'd have to withstand pressures of 10,000-15,000 atmospheres (and the 200 km round-trip too).

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PostPosted: Mon Dec 22, 2008 4:45 am 
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John B Stone wrote:
I am trying to visualize what surface installations would look like on this thing or if there would be any surface features like floating vegetation mats or "forests". Maybe floating towers - a variation on the proposed floating wind turbines.

Hmm, you could probably transport research station gamma to one of these worlds with a few tweaks.


Well considering that waves of 100 ft have been reported by ships in powerful storms here on Earth where the oceans comprise just 70% of the surface area with a average depth of about 11,000 ft I don't think there would be any vegetation mats or forests that could survive the waves on this panthalassic world if they have a corresponding wave height versus depth relationship. With oceans about 50 miles deep the big waves from storms might get up to heights of 2000 to 2500 feet tall. I doubt there would be any large surface installations, most facilities would be submerged probably about to a constant depth of about 4000 to 5000 feet deep. At that depth the surface waves probably do not affect the installations significantly. IMO RS Gamma would have to be converted to a submerged base.

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PostPosted: Mon Dec 22, 2008 5:02 am 
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I wonder how water waves would behave under such surface gravity? Would they be able to break? If not, would you just get huge swells? In that case, surface structures could be viable, because they would just bob up (way up) and down.

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PostPosted: Mon Dec 22, 2008 5:26 am 
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Vile wrote:
I wonder how water waves would behave under such surface gravity? Would they be able to break? If not, would you just get huge swells? In that case, surface structures could be viable, because they would just bob up (way up) and down.


With no solid surface, waves would only be able to get as high as the winds would allow them to get - they usually break when they reach shallows (which don't exist on these worlds). I'd have to find my old oceanography notes to tell you how the waves would behave, but I think you'd have a lot of "fully developed seas" here where the wind's blown far and long enough over the ocean to make the waves as big as they can possibly be under the circumstances. On Earth (in the Southern Ocean) that can be up to 7m tall... on a panthalassic it could be even bigger (though the higher gravity would balance this somewhat I think - that said it might increase the wave speed too). Again, we're going into unknown oceanographic territory here - we don't have anything like this on Earth.

And gods help you if the wind picks up enough to result in hurricanes. The extra mass of the denser atmosphere would wreck anything in its path (though the denser atmosphere would require more energy to actually get moving that fast too). That said, the conditions would be more ripe for hurricanes on warmer water worlds...

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PostPosted: Mon Dec 22, 2008 6:37 pm 
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EDG wrote:
With no solid surface, waves would only be able to get as high as the winds would allow them to get - they usually break when they reach shallows (which don't exist on these worlds). I'd have to find my old oceanography notes to tell you how the waves would behave, but I think you'd have a lot of "fully developed seas" here where the wind's blown far and long enough over the ocean to make the waves as big as they can possibly be under the circumstances.
...

And gods help you if the wind picks up enough to result in hurricanes. The extra mass of the denser atmosphere would wreck anything in its path (though the denser atmosphere would require more energy to actually get moving that fast too). That said, the conditions would be more ripe for hurricanes on warmer water worlds...


Tsunami (tidal wave) cause by an impact or temor might go higher. With the gravity and density being so high (especially the density) once one got started it might travel completely around the planet.
That is assuming that the bottom is smooth.

If the bottom is its own landscape then a tsunami would peak some waves at the points of plateau's or underwater mountains. That would be quite impressive sight to see especially if it was unexpected.
To see suddenly large volumes of water rising up from the ocean and crashing down like a tidal wave on a beach. But since it is crashing down on a water surface which goes back down very deep it could put some of its enegry back into the wave below that is racing on.
Depends on how fast the tsunami is traveling and the size of the mass that caused the spout, as to how much enegry would be transfered back into the tsumnia.

Dave Chase

(Thanks EDG, I corrected the spelling of tsunami. I was writing from memory, my bad.)

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Last edited by Dave Chase on Mon Dec 22, 2008 8:30 pm, edited 1 time in total.

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PostPosted: Mon Dec 22, 2008 7:38 pm 
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Regarding the temperature question, wouldn't the core be quite large and hot? The trend is that the larger the world the longer the core stays molten (Earth is molten, Mars is not). So a Panthellassic world, even in the Outer System will likely have a molten core unless it is very old. That molten core would be a good source of heat for those thermal vents. I would think that Volcanic Vents would be quite common so that chances of life developing might be pretty good if all the other factors line up properly.

HOW a volcanic vent will act with layers of Ice II and Ice V above it might be interesting. I have no idea how that would actually work out.

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PostPosted: Mon Dec 22, 2008 7:42 pm 
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First, it's tsunami, not "tsumnia" :)

Second, tsunami only form because the wave is entering shallow water - in the open ocean they're nothing more than slight, rapidly propagating, long wavelength swells. With no shallows anywhere on this sort of planet, you won't get tsunamis. (not that you won't get big waves - like I said you can get pretty big ones forming in the open ocean because of the fully developed seas. But you can't get proper tsunami here).

See http://en.wikipedia.org/wiki/Tsunami for more info.

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PostPosted: Mon Dec 22, 2008 7:46 pm 
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Cyborg IM1 wrote:
Regarding the temperature question, wouldn't the core be quite large and hot? The trend is that the larger the world the longer the core stays molten (Earth is molten, Mars is not). So a Panthellassic world, even in the Outer System will likely have a molten core unless it is very old. That molten core would be a good source of heat for those thermal vents. I would think that Volcanic Vents would be quite common so that chances of life developing might be pretty good if all the other factors line up properly.


Oh they'd be quite active internally... but the rocky surface can't contact the ocean directly because of all the ice on top of it. And as I said, the extreme pressures would actually act to prevent volcanic vents from forming to start with.

Quote:
HOW a volcanic vent will act with layers of Ice II and Ice V above it might be interesting. I have no idea how that would actually work out.


With the lower pressure forms of ice like ice V or III, a vent might actually have a chance of forming and melting through teh ice. Ice X presents its own problems though because of its high melting point - at best all lava would do is warm it up, not melt it.

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PostPosted: Mon Dec 22, 2008 8:41 pm 
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EDG wrote:
First, it's tsunami, not "tsumnia" :)

Second, tsunami only form because the wave is entering shallow water - in the open ocean they're nothing more than slight, rapidly propagating, long wavelength swells. With no shallows anywhere on this sort of planet, you won't get tsunamis. (not that you won't get big waves - like I said you can get pretty big ones forming in the open ocean because of the fully developed seas. But you can't get proper tsunami here).
....

Thanks EDG, I corrected the spelling in my above post. Wrote from memory, my bad. ;)

OK, I agree and knew that about tsunami waves. But are you telling me that this world has no landscape features, that it is smooth rolling hills at most on the bottom?

If that is true then, my post is absoultely wrong about what could happen on that planet.
A tsunami wave is long wave length that will crest at points in the ocean and then continue along until it runs out of energy or water to transfer its energy. The later is what happens here on earth since there are too many land masses along its direction of travel.

When a tsunami hits a ridgeline of volcano's there is a higher crest of waves at that point. They do not slow down the wave and in most all cases they don't effect its front's shape.

I was using that real world example to explain what might happen on a entirely water world that had no true shallows but might have underwater mountains or plateaus. I was assuming that by having no true shallows that you meant that any underwater landscape would be at least 1000m below sea level. (or at least 1/4 of the depth of the natural bottom. )

Dave Chase

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PostPosted: Mon Dec 22, 2008 11:39 pm 
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Dave Chase wrote:
OK, I agree and knew that about tsunami waves. But are you telling me that this world has no landscape features, that it is smooth rolling hills at most on the bottom?


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.


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I was using that real world example to explain what might happen on a entirely water world that had no true shallows but might have underwater mountains or plateaus. I was assuming that by having no true shallows that you meant that any underwater landscape would be at least 1000m below sea level. (or at least 1/4 of the depth of the natural bottom. )


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!

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