Is it possible for a planet to consist entirely of liquid water, with no core?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Larry Johnson, Jun 10, 2013.

  1. Larry Johnson Banned Banned

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    I understand that some of Jupiter's moons are essentially balls of ice. But if a big ball of ice was near to the sun wouldn't it become liquid? If a hypothetical planet sized ball of water was in orbit around the sun what would it's properties be? What would the effects of gravity be like? What would be in the planet's center? Would the planet be spherical or amorphous?

    I imagine a planet made entirely of water, orbiting the sun at a similar distance to earth, would be like the wax in a lava lamp. I bet it would be fun to live in that planet and play with all the space fish.
     
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  3. KitemanSA Registered Senior Member

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    The water would be dissociated and all you would have left, if anything, would be oxygen. Earth retains its water because of a magnetic field generated by a thorium/uranium/potassium powered liquid iron core over a solid iron core. Pure water, no field, no protection...
     
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  5. billvon Valued Senior Member

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    It would be the same as any other planet. The density of water is 1, whereas the density of the Earth is around 5.5, so gravity would be about 5 times less unless the 'water planet' was larger. The planet would have an atmosphere of something. Either water vapor or some other gas. You'd want an atmosphere of nitrogen or even something denser (like xenon) to prevent rapid loss of atmosphere.

    Being on that planet would be like being in our ocean.

    Note that it would likely have a solid ice core. Even at 'normal' temperatures (i.e. 20 degrees C, 293 degrees K) water is a solid above about 5 Gpa (gigapascal.) At the center of the Earth pressures are around 380 gigapascals.
     
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  7. Kholdstare Banned Banned

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    I do not get how the magnetic field retains water. Can you explain it a little bit?

    According to Antoine Equation the boiling point reduces as water apor pressure reduces.

    log P = A - B/(C+T) , where A, B and C are constants

    within 1≤T≤100, A=8.07131, B=1730.63, C=233.426

    Although this equation is only valid in the range of 1 - 374 degree Centigrade, the trend it shows say that if the log of vapour pressure suddenly becomes zero, the water will start to boil at -19 degree centigrade. What will happen is if water has sudden contact with vacuum, it will start to boil and take the lean heat of evaporation from itself. So when most of the water boils off, some ice will remain.

    However, a planet will an a gaseous atmosphere to cover the water surface might be possible.
     
  8. billvon Valued Senior Member

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    Magnetic field deflects charged particles from the sun. Charged particles, over time, tends to erode away an atmosphere.

    However, our planet generates a magnetic field through convection currents in our (conductive) core. If you postulate a planet of conductive water (say salt water) and a heat source (could be the sun) you could generate a similar field.
     
  9. KitemanSA Registered Senior Member

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    Questionable in the extreme. It is not so much that the core is conductive but iron, no? And the heat source needs to be in the core, not external. The sun would merely stratify the water like it does to the ocean (thermocline).

    Mars was once as wet as earth, they say, but due to a lack of appreciable magnetic field, it lost its atmosphere pretty quickly. About all that is left now is the quite heavy, very stable CO2. Appreciable amounts of that would violate the OP conditions.
     
  10. KitemanSA Registered Senior Member

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    Kholdstare, did billvon's first line of his response answer your question?
     
  11. iceaura Valued Senior Member

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    Would the water at the center of a water globe big enough to retain its water and close enough t0 the sun to have the surface water be liquid, be liquid?
     
  12. Kholdstare Banned Banned

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    Yes. I got the hint from his answer. Charged particles will rub out any atmosphere without magnetic field.
     
  13. billvon Valued Senior Member

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    Jupiter has a powerful magnetic field, and its core is mostly hydrogen. However the hydrogen is so compressed that it is conductive.

    Jupiter's magnetosphere is powered by its own rotation, not by it's internal heat. But in any case, a rotating body being heated unevenly by an external source will not just stratify; like the Earth's oceans, currents will be created by the Coriolis force by the rising and falling of heated (and cooled) water. On Earth, those currents can only circulate in a thin film on the surface of the planet. On a water planet they would extend far beneath the surface of the water, allowing significant current flows - and thus significant magnetic field generation.

    Also note that Europa has a magnetosphere. In that case it is induced primarily by Jupiter's much stronger field, but it is interesting to note that Europa's field is induced primarily in its (conductive) oceans, not in its solid core.
     
  14. Robittybob1 Banned Banned

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    Are you quoting sources or is this your own work?
    I've never heard of a planet with a hydrogen core,. How are you defining "core"?
     
  15. billvon Valued Senior Member

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    No quotes, nor is it my own work; it is the product of about 20 minutes worth of research.

    As the thing in the center. In Jupiter the core is primarily hydrogen under so much pressure that it is more like a metal than a gas. It is where the planet's magnetic field comes from.

    However there is likely also a small solid core made of rocky materials. It's small enough that we can't prove it exists (if it does.)
     
  16. Captain Kremmen All aboard, me Hearties! Valued Senior Member

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    It's his own work.
    From his Jovian core expedition.
     
  17. Robittybob1 Banned Banned

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    From:
    http://science.nasa.gov/science-news/science-at-nasa/2011/09aug_juno3/
    From the diagrams that core might be small in terms of the size of the whole planet but would still be as big as Mars. I'm searching for possible estimates of the mass and dimensions of the core.
     
  18. Larry Johnson Banned Banned

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    Thanks guys

    So what your saying is that I would just have a big cloud of oxygen? Will that even be a planet? Like an oxygen based Jupiter? Could things still live in it, like flying creatures?

    Is there no other way I can retain some kind of atmosphere on my planet without having a magnetic core?
     
  19. billvon Valued Senior Member

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    Sure, keep making gas. Constant volcanic eruptions, for example, could keep an atmosphere for millennia.
     
  20. KitemanSA Registered Senior Member

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    Actually, two ways, one that sort of contradicts my prior statement and one that doesn't.

    It is possible to have a planet of pure water, but not one of pure LIGUID water. To keep the hydrogen near the sun, the planet would have to be VERY large and that size would surely result in a solid water core. Violates the OP.


    The second is to have only heavy elements in the gasses in the atmosphere. Venus has both a dense atmosphere and no significant magnetic field. But the atmosphere is dominantly made of CO2. CO2 is much harder to ionize than water and the resultant velocity doesn't often exceed the escape velocity. But CO2 violates the OP.
     

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