Planetary Formation - Liquid planet

[BMAONE23]

(This thread was split from Planetary Formation, please go there for any missing posts - makc)

The problem with water in space is that it would take atmospheric pressure to prevent it from sublimating directly to space and it would take relatively high temperatures to keep it in liquid form to allow for the time needed for the dissolved solids in the water to form around the molecule involved in the experiment. Space is a Cold, Pressureless, near void in which water molecules can only survive as Ice (cold) or individual molecules (pressureless) or in the form of hydrates. The more Water molecules you bring together in space, the best you can form is a comet of increasing size. It takes the mass of a planet, proxcimity to a star (0.7 - 1.3AU or so) for warmth and atmospheric pressure to maintain liquid water at the surface. Now what you propose could be happening to a small extent on some of the distant moons that may have liquid oceans but not to the extent of forming planetary bodies.

[BMAONE23]

Q) Can water, if containing enough dissolved iron solids, become magnetized and display signs of polarity?

If so, a totally liquid planet (as seen in a Star Trek Voager episode) might be hypothetically possible IF it were to have enough mass to retain an atmosphere, be close enough to its parent star so that the water remains liquid, and be able to generate an active magnetic field to prevent solar induced atmospheric loss to space. But, assuming that the water contains the same ammount of dissolved solids as our earth does, the planet would only be able to produce a miniscule core before there weren't and solids remaining in the water. There would need to be a steady infusion of solid material from off world sources to both maintain dissolved solid:water ratio and to allow for a rocky planetary body to form.
So If water containing dissolved Iron Solids could not become magnetized, the proposed world could not exist naturally.

[Chris Peterson]

Q) Can water, if containing enough dissolved iron solids, become magnetized and display signs of polarity?

If so, a totally liquid planet (as seen in a Star Trek Voager episode) might be hypothetically possible IF it were to have enough mass to retain an atmosphere, be close enough to its parent star so that the water remains liquid, and be able to generate an active magnetic field to prevent solar induced atmospheric loss to space. But, assuming that the water contains the same ammount of dissolved solids as our earth does, the planet would only be able to produce a miniscule core before there weren't and solids remaining in the water. There would need to be a steady infusion of solid material from off world sources to both maintain dissolved solid:water ratio and to allow for a rocky planetary body to form.
So If water containing dissolved Iron Solids could not become magnetized, the proposed world could not exist naturally.

I think there are additional problems, as well. Iron atoms are not ferromagnetic; you need to get them into a crystalline or semi-crystalline state so that magnetic domains form. So I don't see how iron dissolved in water can ever result in a magnetic field. As far as we know, planetary magnetic fields are created by dynamo effects, the product of moving, liquid iron cores. When a planet cools enough that its core is no longer liquid, it loses most of its magnetic field.

Another problem is that you can't have a liquid water planet as you describe it. If the planet is large enough to be able to hold an atmosphere, you don't have to go very far below the surface before the pressure is above a few gigapascals. At such pressures, water only can exist as a solid. So what you effectively end up with is a solid planet with a relatively thin liquid layer. Presumably, reactions based on dissolved material in such an ocean would be similar to what might happen on a rocky planet.

[Qev]

Another problem is that you can't have a liquid water planet as you describe it. If the planet is large enough to be able to hold an atmosphere, you don't have to go very far below the surface before the pressure is above a few gigapascals. At such pressures, water only can exist as a solid. So what you effectively end up with is a solid planet with a relatively thin liquid layer. Presumably, reactions based on dissolved material in such an ocean would be similar to what might happen on a rocky planet.

This is probably a little off-topic for this thread, Chris, but do you know if anyone has modelled what the interior of an Earth-sized water planet would be like? I've been curious about such a thing for a while now.

[Chris Peterson]

This is probably a little off-topic for this thread, Chris, but do you know if anyone has modelled what the interior of an Earth-sized water planet would be like? I've been curious about such a thing for a while now. :)

I don't know. But this discussion has made me consider giving it a shot. A first approximation shouldn't be too difficult, since the phase diagram for water is well defined, and water's density doesn't change much with pressure (which means the gravitational field as a function of depth is easily defined). The first thing to figure out is the minimum size necessary to hold a water vapor atmosphere at sufficient pressure to allow a liquid surface, and with an escape time into space that is reasonably low.

[Doum]

Chris said,
"The first thing to figure out is the minimum size necessary to hold a water vapor atmosphere at sufficient pressure to allow a liquid surface, and with an escape time into space that is reasonably low."

For that to be possible i think it will have to happen only around a brown dwarf star up to a red dwarf star . Bigger star then that (M type or more) and the water molecule will be broken to ion by the UV of a sun or high heat. It will also forbid the accretion of water.

Right now, even at mars distance, the water is vaporising or its molecule broken whether its on a comet or on mars surface. So mars is loosing water. Also is earth. So it must be a small star that deliver only low energy to keep water at liquid temperature. As for creating a crust with molecule or dissolve iron or any other elements of the periodic table trough diffusion into that ball of water up to an earth size planet i realy dont think so. Because, to have a water planet being create, there must not be any dust closeby around that star or it will be a normal accretion planet.

[Chris Peterson]

Chris said,
"The first thing to figure out is the minimum size necessary to hold a water vapor atmosphere at sufficient pressure to allow a liquid surface, and with an escape time into space that is reasonably low."

For that to be possible i think it will have to happen only around a brown dwarf star up to a red dwarf star . Bigger star then that (M type or more) and the water molecule will be broken to ion by the UV of a sun or high heat. It will also forbid the accretion of water.

To be clear, I do not believe it is possible under any likely circumstances for a water planet to form naturally. So I'm not considering a natural body here, only considering what the physical characteristics of such a body would look like.

[apodman]

I abandoned the "water" idea for a moment to see how the last "liquid" planet I heard about was doing. That's Uranus with liquid ammonia and liquid methane. I was surprised to find that now some think there is solid and even rock at the core, but I was unable to identify a prevailing view. Is there one?

[Chris Peterson]

I abandoned the "water" idea for a moment to see how the last "liquid" planet I heard about was doing. That's Uranus with liquid ammonia and liquid methane. I was surprised to find that now some think there is solid and even rock at the core, but I was unable to identify a prevailing view. Is there one?

I'm pretty sure that all modern models of Uranus's interior require a rocky core. Also, the intermediate layer, what you are calling liquid ammonia and methane (and also contains water) would be better described as a fluid ice layer, not a liquid layer. It certainly behaves nothing like a liquid ocean in any context we are familiar with.

[Doum]

Right Chris,

I just realise that to have water molecule around a star you will need oxygen wich come from a star explosion (Supernova). So all element from oxygen to hydrogen (At least) had been present in that star explosion and have to be present in the vicinity of that new star. I dont think there is a natural phenomenon that can separate oxygen and hydrogen from all those elements and that will also remove all those other elements from the vicinity of that star. So, it seem that water planets being naturaly form is not likely. More a fiction then a possible reality.

[Qev]

This is probably a little off-topic for this thread, Chris, but do you know if anyone has modelled what the interior of an Earth-sized water planet would be like? I've been curious about such a thing for a while now.

I don't know. But this discussion has made me consider giving it a shot. A first approximation shouldn't be too difficult, since the phase diagram for water is well defined, and water's density doesn't change much with pressure (which means the gravitational field as a function of depth is easily defined). The first thing to figure out is the minimum size necessary to hold a water vapor atmosphere at sufficient pressure to allow a liquid surface, and with an escape time into space that is reasonably low.

I suppose I should have said 'Earth-mass' instead of 'Earth-sized'... that, at least, would make the question of gravity fairly simple.

I've run across a paper that at least touches on the subject, Mass-Radius Relationships for Solid Exoplanets by Seager, Kuchner, et al. It's rough going for me though, I'm afraid... there's a lot of rust on my math skills.

[Doum]

Before the tread is close here are the different phase for water under different temperature and pressure.

http://en.wikipedia.org/wiki/Supercriti ... se_diagram

Enjoy.

[Qev]

Before the tread is close here are the different phase for water under different temperature and pressure.

http://en.wikipedia.org/wiki/Supercriti ... se_diagram

Enjoy.

I found this one while stumbling around doing some water-planet research. It's delightfully detailed.

http://www.lsbu.ac.uk/water/phase.html

[Doum]

A very good one Qev. Thanks.

[Doum]

New data. Jupiter with a big rocky core?

http://www.space.com/scienceastronomy/0 ... -core.html

[bystander]

Habitable Planets: Four Types Proposed
Astrobiology Magazine - Space.com - 2008 Dec 18

• 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."

[Chris Peterson]

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.

It makes perfect sense that you could have water planets. But in the context of this discussion, it's important to recognize that a water planet is not a liquid planet.

[Qev]

Any thoughts on how one would estimate how the temperature would change with depth on this Earth-sized water planet?

[Chris Peterson]

Any thoughts on how one would estimate how the temperature would change with depth on this Earth-sized water planet?

There's no way to answer this without putting more constraints on the question. The internal heat of a planet comes from a combination of residual heat of formation, radioisotope decay, and tidal effects. So you'd have to know the age and formation history of the body, whether it was pure water or contained radioisotopes, and whether it had a large moon or orbited very close to a star. Certainly the range of possibilities includes a body with no temperature gradient at all, to one with an interior at thousands of K.

[makc]

let's say some magic force installed huge ball of water with 1 earth mass and no temperature gradient at 1 au from sun-like star. let's say it doesnt spin (to avoid all sort of problems with internal currents), so 1 day (+night) takes whole year. my guts are telling me this is not balanced system, and so it will change towards its balance point. how do we tell what would that be?

[Chris Peterson]

let's say some magic force installed huge ball of water with 1 earth mass and no temperature gradient at 1 au from sun-like star. let's say it doesnt spin (to avoid all sort of problems with internal currents), so 1 day (+night) takes whole year. my guts are telling me this is not balanced system, and so it will change towards its balance point. how do we tell what would that be?

Well, most of it will be water ice in an exotic state (very high pressure); that state will probably be fluid, just like the interior of the Earth is fluid frozen rock. Such fluids are basically solids that show plasticity; they would appear solid to casual observation.

Whether the surface was frozen or liquid would depend on how the atmosphere evolved. The emissivity of water is such that at 1 AU it won't absorb enough heat from the Sun to warm above its freezing point. Earth has liquid water because of the greenhouse effect of its atmosphere. Water vapor is a strong greenhouse gas, so if the body had enough time to evaporate an atmosphere, it should have liquid oceans. It might also freeze, but sublimate an atmosphere over time and then thaw. That seems like a complicated dynamic to analyze.

There will obviously be a weak radial temperature gradient for a long time. I expect you'd see some (very slow) internal convection. Since the object is specified to be tidally locked to the Sun (which doesn't mean it doesn't spin, BTW), there will also be some kind of gradient through the body from the sunlit to dark side. If there's an atmosphere, being tidally locked will drive a hellacious weather system. I think the situation would be easier to analyze if you allowed for a higher rotation rate, or no rotation at all.

[bystander]

let's say it doesnt spin (to avoid all sort of problems with internal currents), so 1 day (+night) takes whole year.

Since the object is specified to be tidally locked to the Sun (which doesn't mean it doesn't spin, BTW), there will also be some kind of gradient through the body from the sunlit to dark side. If there's an atmosphere, being tidally locked will drive a hellacious weather system. I think the situation would be easier to analyze if you allowed for a higher rotation rate, or no rotation at all.

makc's spec clearly states no-spin. 1 day = 1 year. Day/night cycle driven by orbit only, no revolution. 1:1 tidal lock implies 1 revolution for each orbit.

[Chris Peterson]

makc's spec clearly states no-spin. 1 day = 1 year. Day/night cycle driven by orbit only, no revolution. 1:1 tidal lock implies 1 revolution for each orbit.

Okay. It's a little confusing because a body in 1:1 resonance is often said to have its day equal to its year.

[makc]

That seems like a complicated dynamic to analyze.

What constraints, in your oppinion, can simplify this more?

[harry]

G'day from the land of zzzzzzzzz


Planet formation
http://arxiv.org/abs/0806.3788
Ice Lines, Planetesimal Composition and Solid Surface Density in the Solar Nebula

Authors: Sarah E. Dodson-Robinson (1), Karen Willacy (2), Peter Bodenheimer (3), Neal J. Turner (2), C. A. Beichman (1,2) ((1) NASA Exoplanet Science Center, (2) Jet Propulsion Laboratory, (3) UCO/Lick Observatory)
(Submitted on 23 Jun 2008 (v1), last revised 4 Dec 2008 (this version, v2))

Abstract: To date, there is no core accretion simulation that can successfully account for the formation of Uranus or Neptune within the observed 2-3 Myr lifetimes of protoplanetary disks. Since solid accretion rate is directly proportional to the available planetesimal surface density, one way to speed up planet formation is to take a full accounting of all the planetesimal-forming solids present in the solar nebula. By combining a viscously evolving protostellar disk with a kinetic model of ice formation, we calculate the solid surface density in the solar nebula as a function of heliocentric distance and time. We find three effects that strongly favor giant planet formation: (1) a decretion flow that brings mass from the inner solar nebula to the giant planet-forming region, (2) recent lab results (Collings et al. 2004) showing that the ammonia and water ice lines should coincide, and (3) the presence of a substantial amount of methane ice in the trans-Saturnian region. Our results show higher solid surface densities than assumed in the core accretion models of Pollack et al. (1996) by a factor of 3 to 4 throughout the trans-Saturnian region. We also discuss the location of ice lines and their movement through the solar nebula, and provide new constraints on the possible initial disk configurations from gravitational stability arguments.