Gravity & Water

[Azimov]

If a planet consisted of nothing but water (unlikely I know but bear with me) would the 'core' be superheated and gaseous and if so would the bubbles rise to the surface? Could such a 'planet' even exist? Please don't draw any comparisons with the Waterworld movie, I believe that was a planet 'covered' with water not a planet 'made' entirely of water!

[spiff]

Blimey! this one's got me thinking!! If the world was pure water,then the outside would freeze. This would reflect sunlight making the planet colder,so the ice would increase.But then,the pressure would stop the water from freezing at some point. I reckon you would end up with a world that might freeze then melt in cycles. Damn good question Asimov!!

[Hamish]

As you compress a liquid its boiling point increases. Also water has some unusual phase (solid/liquid/gas) behaviour. You would need to specify how big the planet was and if it had an atmosphere. It would seem most likely that the core would be very hot liquid water, but it is possible that the water (H2O) might dissociate at high enough temps to give H2 and O2 these might escape or become dissolved in the water. At any rate some sort of equilibrium would be reached.

[anthomson]

Just a thought, wouldn't a planet consisting of water be similar to in composition to a comet. If so wouldn't it be frozen on the inside and gaseous on the surface.

[incitatus]

nope- what happens is that as you get to the core the pressure is sufficient to rasise the boiling and melting points of the fluid so that it does not boil. look at jupiter- made of gas, with a liquid mantle and a core osf solid hydrogen. Only works for largish planets though, otherwise its comet time

[Azimov]

Assuming that this imaginary planet was of sufficient size (ie something of the magnitude of Earth) then what would be the processes involved? I was considering a situation involving a superheated core and a frozen surface. What intrigues me is the status of the matter in between, how it behaves, the areas between it's superheated and frozen states. And then there's those bubbles!

[spiff]

the bubbles, if any, might lead to a layer of "atmosphere" at the boundry of the hot/cold conditions.maybe.mmm...

[thekraut]

Sorry, you guys, but where should the energy to "superheat" the core come from . jjust because earth has a hot center doesn't automatically mean that this would be the case for our biiiiig drop. and as for the bubbles: at a sufficient depth, pressure reaches the critical point, ergo no bubbles there. besides, evaporating water needs loads of enegy - which would have to be produced at some point. in my opinion you would either end up with a ball of ice or liquid, depending if gravity is big enough to keep an atmosphere. bleibt froehlich

[Azimov]

Wouldn't the enormous pressure at the core be enough to cause the temperature to rise to superheated levels, assuming the planet was of sufficient size? Or could the core never be superheated no matter how big the planet was?

[thekraut]

I think that even if you had a superheated core at some point (maybe during or directly after the formation of the planet) this state would not be the equilibrium state. without an energy source in the center, equilibrium should be: same temperature for all depths, but different pressures of course. and you have to bear in mind that pressure alone can't cause a liquid to heat up (due to it's incompressibility (is that english?). don't mix it up with collapsing gas clouds/forming stars. there you get a temperature rise from compression, the particles' kinetic energy being transformed into heat and the fusion reaction that starts if temp. and pressure are sufficiently high. none of these apply to our water planet.