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Thread: Earth's magnetic field

  1. #1 Earth's magnetic field 
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    It is believed that there is molten metal (iron) within the core of the earth and that this molten metal moves due to the earth's rotation and convection. We know that magnetic fields are generated by electric currents. But why should an electric current be associated with a flow of molten metal?


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    Forum Professor pyoko's Avatar
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    I would have a quick read of this, it's not long:

    Magnetic Field of the Earth


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    Thanks - but I have read several web pages, including the one you refer to, and none explain why a flow of molten metal on its own should give rise to an electric current. To do that, the molten metal would have to carry a net charge - but where would that come from?
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    Forum Professor pyoko's Avatar
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    Would you be satisfied that is has something to do with Dynamo theory - Wikipedia, the free encyclopedia , but basically we are not sure yet?
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    I have read that too. Again, it doesn't explain the underlying source of the electric current. A conductor moving in a magnetic field will have an emf induced in it - the dynamo effect - but this presupposes the existence of the magnetic field whose origin we are trying to explain.
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    Forum Professor pyoko's Avatar
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    I don't think they are too sure yet and the best simulations have not yet managed to replicate it. Maybe someone here can give us a hypothesis.
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    Moderator Moderator Markus Hanke's Avatar
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    From what I know it is a dynamic feedback system - electric current loops in the outer core generate changing magnetic fields, and changing magnetic fields in turn induce electric currents. It is a highly complex, non-linear system. The really interesting question is why and how it first started...
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    My guess is that the Earth's Dynamo is a shell of semi-solid iron-nickel formed by the high pressures within the earth. To be magnetic, this shell has to be split somewhere to form the North and the South poles. As this iron shell fractures and rebinds due to expansion and the bulging at the equator, the spinning planet creates our magnetic field. We know that the magnetic field both moves and flips. I attribute this to motion of the iron shell and when two sides crack flipping the polarity. ???
    Earth's Inconstant Magnetic Field - NASA Science


    ..............................
    4_1_5_0_magnetic_01.jpg
    http://www.mnh.si.edu/earth/text/4_1_5_0.html

    proton .....
    Last edited by proton; November 4th, 2012 at 01:58 PM.
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    Forum Bachelors Degree Kerling's Avatar
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    Hm well it is a complex thing, but yes there is no moving charge (except perhaps in the degenerat core, but that is not of the matter)

    The effect has to do with the gradual cooling of our planet. And the fact that it rotates. That is very important. And not all of the mantle is iron. Just parts. Put the iron parts can be causing small loops of current due to their change in flux. Now on earth, where magnetic fields dissipate easily, this isn't such the case. But in a very hot environment like the mantle conductivity is really really low. This cause fields to be sustained. But they are trouble by particles which move through the field, but don't want to, who create a new field in their turn. Sustaining the field and what little charge does move will strengthen this field. As due to the conductivity charge cannot easily escape. Together they form the magnetic field.
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    pyoko,

    ......Maybe someone here can give us a hypothesis.
    Here are two hypothesis. The first tries to explain the present dynamo model via electrical current flow in a liquid core. As the Earth rotates there is a relative difference between the relative motion of the Earths surface and liquid core. As a liquid or gas flows relative to solid, the liquid/ gas ionizes losing electrons via friction with the solid. This is the basis for lightening. The atmosphere is ionized and during a storm current/electrons flows from the Earth to the clouds to reduce the ionized potential while neutralizing atmospheric molecules.

    For similar reasons a liquid rotation core could lose electrons via friction with a solid core and the Earth's crust. This accordingly would create a continuous electrical potential and current flowing through the liquid core from a solid core and/or crust. This electrical potential accordingly would be expressed at the surface via the Earth's magnetic field.

    Another hypothesis is that the dynamo model is the wrong theory of geo-magnetism. There have been alternative models proposed where the relative spin of the atmosphere and oceans create discontinuous ocean electrical currents that create the Earth's magnetic field. In this model the Earth's core would have nothing to do with the Earth's magnetic field.

    Earth
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    Forum Professor pyoko's Avatar
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    Yeah, that second one somehow seems unlikely. Still interesting, thanks.
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    Quote Originally Posted by Markus Hanke View Post
    From what I know it is a dynamic feedback system - electric current loops in the outer core generate changing magnetic fields, and changing magnetic fields in turn induce electric currents. It is a highly complex, non-linear system. The really interesting question is why and how it first started...
    The origin of the Earth's magnetic field is a great question, one that ought to be approached with a great deal of humility and respect for the complex workings of nature. Lately heliophysicists have been working hard on understanding the operation and origin of our sun's magnetic field, into which the Earth is deeply embedded and connected. Very recent research throws doubt on ALL previous hypotheses. Partly because of the difficulty in studying the inner portions of the Earth, it may be apposite to look at the sun for clues regarding Earth's magnetic field.

    Researchers Create
    http://arxiv.org/pdf/1206.3173.pdf
    “However, our results suggest that convective motions in the Sun are nearly 100 times smaller than these current theoretical expectations,” continued Hanasoge, also a postdoctoral fellow at the Max Plank Institute in Katlenburg-Lindau, Germany. “If these motions are indeed that slow in the Sun, then the most widely accepted theory concerning the generation of solar magnetic field is broken, leaving us with no compelling theory to explain its generation of magnetic fields and the need to overhaul our understanding of the physics of the Sun’s interior.”

    Respectfully submitted,
    Steve
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    Quote Originally Posted by Dotini View Post
    Quote Originally Posted by Markus Hanke View Post
    From what I know it is a dynamic feedback system - electric current loops in the outer core generate changing magnetic fields, and changing magnetic fields in turn induce electric currents. It is a highly complex, non-linear system. The really interesting question is why and how it first started...
    The origin of the Earth's magnetic field is a great question, one that ought to be approached with a great deal of humility and respect for the complex workings of nature. Lately heliophysicists have been working hard on understanding the operation and origin of our sun's magnetic field, into which the Earth is deeply embedded and connected. Very recent research throws doubt on ALL previous hypotheses. Partly because of the difficulty in studying the inner portions of the Earth, it may be apposite to look at the sun for clues regarding Earth's magnetic field.

    Researchers Create
    http://arxiv.org/pdf/1206.3173.pdf
    “However, our results suggest that convective motions in the Sun are nearly 100 times smaller than these current theoretical expectations,” continued Hanasoge, also a postdoctoral fellow at the Max Plank Institute in Katlenburg-Lindau, Germany. “If these motions are indeed that slow in the Sun, then the most widely accepted theory concerning the generation of solar magnetic field is broken, leaving us with no compelling theory to explain its generation of magnetic fields and the need to overhaul our understanding of the physics of the Sun’s interior.”

    Respectfully submitted,
    Steve
    Planetary magnetism is very divergent in our solar system as discovered by our satellite probes of them. I think it provides many clues to how planetary and maybe stellar magnetism works, including the Earth and sun. Although the dynamo model of geo-magnetism has long been the leading theory it has also long been suspect as to the validity of its tenets. Much of the Earth's iron core is molten but molten iron in non-magnetic. Although electric currents seem that they likely flow within the core, the core is a very long distance away from the Earth's surface and the insulation of the crust might prevent magnetic influences of the core from reaching the Earth's surface.

    Convection currents of heat influence currents of the sun's plasma and are presently thought by studies to be much weaker than needed to produce the sun's very strong magnetic field. The sun is a large volume of plasma including protons, neutrons and electrons and not a wonder that the sun and other stars would have large magnetic fields. The question is the mechanics of stellar plasma's internal motions.

    Presently the Earth's magnetic field is half way between the Earth's rotation poles and the plain of the solar system. So the sun's magnetic field seems to have a big influence on the Earth's magnetic field.

    Stars and planets which have a large atmosphere and rapid rotation rates have large volumes of ionic currents. Electrons in motion produce magnetism. I think it's just a matter of determining how these currents interact with each other and the solar wind concerning the planets, to produce their observed magnetic fields, or lack thereof.
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