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The Earth's Mysterious Magnetosphere
Date: 17th September 2004.
Author: Greg Alexander
We are informed that the Earth’s magnetic field, which stretches far out into space, is capable of deflecting the myriads of charged particles streaming from the Sun commonly known as the ‘solar wind’. In this respect it forms a natural barrier against these sometimes highly energetic particles.
Although this sounds straightforward enough, knowing in detail how the exact physics works with regard to moving charges or currents being acted upon by magnetic fields how is the Earth’s magnetosphere actually able to do this?
For example we are informed that in this instance Fleming’s left-hand rule would apply. This easy to remember guide has the thumb, forefinger and second finger extended in such a way that a right-angle is formed between each. The second finger represents the direction of motion of the charged particle or current (the two being identical and hence interchangeable), while the forefinger represents the direction of the field and the thumb the direction of the resultant force.
However if you apply this rule to a charged particle which is speeding towards the Earth the following would occur: pointing your second finger towards an appropriately spherical object representing the Earth and with your forefinger pointing directly up showing the direction of the magnetic field to north, the particle will tend to be deflected sideways to the East. In the case of a particle which is arriving at the east-side of the Earth, the particle will be deflected away and out into space. However if the particle is arriving at the west-side of the Earth it will be deflected directly into the Earth itself. It is clear from this therefore that just as many particles will be deflected towards the Earth as will be deflected away. It would appear from this therefore that the Earth’s magnetosphere would not act as the natural barrier against the solar wind as has been made out.
The picture given by astrophysicists is that particles from the Sun hit the Earth’s magnetosphere forming a ‘bow shock wave’. The particles then stream in all directions around the magnetosphere, taking curved paths as they do so, and then head out directly behind the Earth in a straight line. The result of this is that the Earth’s magnetosphere becomes stretched out forming a ‘tail’ which points directly away from the Sun. In this respect its shape very much resembles that of a comet. The particles which get inside of this natural barrier and which give rise to the aurorae (the northern and southern lights) are said to ‘leach in’ either from behind the Earth via the magnetotail or via the poles when the field lines continually rejoin as a result of the Earth’s rotation.
But how can charged particles which are accelerating in a magnetic field, form queues and then move out in all directions around the Earth despite of the direction of the field lines? Indeed considering how rarefied the solar wind is (perhaps a dozen charged particles per cubic centimetre) how is it possible to speak of a shock wave as well?
If the physical laws which describe the forces acting upon a charged particle moving within a magnetic field are at all reliable, then the Earth’s magnetosphere should not work in the manner pictured above. Indeed it would not act as a ‘shield’ at all in this respect but the charged particles in question would directly bombard the Earth’s ionosphere (the layer of hot, ionised gas immediately surrounding the upper atmosphere).
But what of the allegedly scientifically accurate measurements of such particles made both by satellites in Earth orbit and by probes outside of the magnetosphere? The data they are stated to have gathered strongly correlates with the accepted picture which we have shown cannot be the case anyway. So how are we to reconcile physics theory with the observational data gained?
Even taking into account the magnetic field brought by the solar wind itself (which is an extension of the Sun’s own magnetic field), the shield-like qualities of the Earth’s magnetosphere are still a mystery. The Sun’s magnetic field at the Earth is thousands of times less intense than the Earth’s itself so this factor would not make a great deal of difference either.
We are also left wondering whether the Van Allen belts that are spoken of would really exist either. These take the form of two concentric doughnut shapes above the Earth’s equator in which trapped particles of certain energy levels circulate. Discovered by the early Explorer satellites, they are described as ‘radiation belts’ existing within the Earth’s magnetosphere. Considering that charged particles probably do not ‘leach in’ through the magnetopause (the boundary between the Earth’s magnetic field and that of the Sun), it is questionable whether they could become trapped in this way anyway.
It is also the case that ‘cosmic rays’ interact directly with the Earth’s atmosphere without being deflected by the magnetosphere. These rays not only come from galactic sources but also from the Sun. They take the form of charged particles travelling at relativistic velocities. However it must also be noted that these same cosmic rays coming from the Sun make up part of the solar wind. So how can it be said therefore that the Earth’s magnetosphere only deflects some charged particles from the Sun and not others?
It is also the case that the vast bulk of the charged particles making up the solar wind have strikingly different masses. For example there are not only high velocity electrons but also high velocity protons. Considering that electrons and protons have the same charge, though of course exactly opposite, and that the mass of a proton is about 1840 times as great as that of an electron, would it not be the case that the protons would be deflected by only 1/1840th of that with the electrons? On this consideration alone it is apparent that the Earth’s magnetosphere would not act as the same barrier with respect protons as it would with electrons.
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