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Net Charge of Planets and Stars

  1. May 23, 2008 #1
    The earth is effectively an insulator in space, and the sun continuously beats on the earth with protons, electrons and other particles.

    Does the planet earth and all other planets have a net charge, and if so, how can we measure the polarity and extent of that charge?

    Turning to the Sun and the stars, do they have a net charge, and if so, how could it be measured?
  2. jcsd
  3. May 23, 2008 #2

    From what i've seen it hasnt been directly mearsured. You'd need to take varying measurements of the E-field produced at varying radi to work out the PD at each point, but I think thats harder to do in practise than it sounds. Its known that neutron stars and "quark stars" possess a spherical electrosphere from their charge, but i'm not sure about planets or the sun. You should beable to see a spherical E-field field surrounding the sun if it had a significant charge, but I dont think we've ever seen that. Theres a few predictions based on electric polarization, basically involving the separation of electrons from their orbits in the gravitational field, but they remain very theoretical at this point, and not many other publications have followed this idea I dont think. They predict ~100 C net charge, which is hardly significant compared to the size of the sun.

    This paper gives a good summary (I cant post links yet, just search this paper title) "On the global electrostatic charge of stars" Astronomy and Astrophysics, v.372, p.913-915 (2001)

    One thing I read in my physics book the other day, implies that the Earth is pretty much neutral, I'll quote it;

    Which implies that the positive out = the negative in, so it will remain largely neutral. Unless theres a delay in this process...
  4. May 23, 2008 #3


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    I don't get this thunderstorm argument - these are currents (up and down) that go in the thin atmospheric layer, they shouldn't effect the overall Earth charge, just like electric sparks in the lab don't change electrical neutrality of the building :smile:

    Or am I missing something?

    Last edited by a moderator: Aug 13, 2013
  5. May 23, 2008 #4

    No I dont think so, I think thats pretty much it. If there was a net charge, it would probably alternate between positive and negative between each strike. I think that the positive lightning travels upwards (sprites?) and generally negative lightning down. But I cant be sure. There may be a completely different process at work for all I know, and my textbook that I read this from is only A-level grade, so its probably a simplified explanation anyway :)
  6. May 23, 2008 #5

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    The earth's average electric field at the surface is about 600 V/m. While Borek is right - this doesn't extend to all space, but is canceled by charge in the upper atmosphere, we can use this as an upper limit to the earth's charge imbalance, and it's neutral to about one part in 10^26. That is, one extra (or missing) electron per kilogram of matter.

    Most everyday objects are not nearly this neutral.

    The extreme neutrality is because of the solar wind. If the earth had a large positive charge, it would preferentially deflect protons and absorb electrons until that charge is canceled out. (And the reverse for a negative charge)
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