Planetary Magnetism - A Heretic's View

by Wilf James
(Click on the images to see enlarged versions.)
Updated 22nd September 2006

Author's Note November 2009
This essay was started more than 10 years ago in 1999, shortly after I had learned enough about the internet to create my own website. The reader will see at the end how it has been modified since then. In 2009 I decided to try to write a more organised essay to cover many of the points raised in this essay in a simple way with the minimum of mathematics. In so doing I found that I had stumbled upon an answer to something that had mystified me about the apparent coolness of sunspots. I also wanted to expose what I call the Maxwell Myth that electricity and magnetism are equivalent. As this essay has evolved over time, so has my thinking about what I describe on my business card as "Errors Found In Astronomy Books". I would like you to read this first so that you can follow the evolution of my thinking about this subject. If you read this after reading Basic Electricity and Magnetism For Astronomers you will be able to see how that essay represents how my thoughts about the subject have. developed.

Additions May 2012
New attempts to describe magnetic phenomena on the Earth and on the Sun are:
Earth's Magnetism
The Sun's Magnetism
Astronomical Howlers

A Preface

I never thought of starting this essay with a quotation but I have just found one from Galileo, reviewing William Gilbert's treatise on magnetism:

"I extremely praise, admire and envy this author. I think him moreover worthy of the greatest praise for the many new and true observations that he has made, to the disgrace of so many vain and fabling authors, who write, not from their own knowledge, but repeat everything they hear from the foolish vulgar, without attempting to satisfy themselves of the same by experiment, perhaps that they may not diminish the size of their books."

In the context of this essay I would change Galileo's 'hear from the foolish vulgar" to 'have read in other books'. I also think that the reference to William Gilbert's treatise on magnetism is appropriate to what I have written here..

Self Introduction
I have studied astronomy on and off for more than 40 years - including a one-year course on the Solar System with Ian Nicholson at the Hatfield Polytechnic. (It is now called The University of Hertfordshire.) I have been involved with electricity and electronics for even longer. As a result I have become increasingly dissatisfied with certain aspects of the 'accepted wisdom' promulgated in the books I have read on astronomy. In almost all references to the magnetic fields in the Solar System there seems to be a pre-supposition that they are 'just there' and all movements of ionised gases are affected by the presence of these fields. The references to magnetic fields tend to treat them as the causes of events rather than the reverse.

Beginnings
When I was about eight I was given a book which included information about electricity and magnetism. The book contained a drawing showing a battery, a bulb and a coil of wire in a simple circuit. Near the coil was a compass. I made up the circuit and checked to see if what was written about coils, electricity and magnetism was right. The compass moved when the bulb was lit. It moved back again when the battery was disconnected. From then onwards I have been convinced that electricity always comes before magnetism. It is not a chicken and egg question about which came first. Electricity was first produced in the universe when gases that were hot enough to be ionised began to move, or, when moving gases became hot enough to be ionised. Magnetism was created by the movement of these ionised gases.

Every magnet that ever existed has been created by the primary or secondary effect of an electric current. When a magnet has been made, it can transmit some magnetism to another piece of unmagnetised magnetic material. Unmagnetised magnetic material cannot become magnetised spontaneously.

The Earth's Dynamo Theory
In my studies I have learned about the solar wind and I have read and understood the theory of the Earth's dynamo, based on flows of liquid iron within the Earth. However, this theory does not seem to make much sense to me for several reasons. The main reason is the 'standard' explanation of the circular movement of iron within the Earth. The easiest way to check this is by using a gyroscope as an analogue. The flywheel of a gyroscope is usually made of a conducting metal. How effective would a gyroscope be if it generated a magnetic field as it spun? Gyroscopes do not generate magnetic fields because the atoms and molecules that make up the flywheel are electrically neutral. Any currents generated in one direction are cancelled by currents in the opposite direction. A gyroscope flywheel does not generate a magnetic field, no matter what metal is used to make it or how fast it is rotated.
Note
A spinning metal disc in a magnetic field will slow down quickly. Currents induced in the disc by the magnetic field are effectively short circuited. These currents heat the disc somewhat, the heat energy being extracted from the mechanical energy used to make the disc spin. This principle is used as the magnetic braking system in electricity consumption meters.

Fluid metals and Convection
The iron in the Earth's core must be mobile for the liquid iron dynamo to work. If it is mobile, it must have been stirred and mixed to be in an homogeneous state over geological time. In other words it is likely to be electrically neutral. Neutral rotating conductors generate no electricity, and therefore, no magnetism. Another factor which is often overlooked is that metals are generally good conductors of heat. The concept of convection is mainly noticeable with water and air. Both of which are very bad conductors of heat. Convection is caused by a heated part of a fluid becoming less dense than its surroundings and therefore likely to float upwards within the fluid. With metals like iron and nickel which are presumed to form most of the Earth's core, their relatively high rate of heat conduction will tend to prevent any part from being significantly hotter than its neighbours. Thus it will not be significantly less dense than its neighbours. The motivation for upward movement will therefore be correspondingly low. Any upward movement of a hot piece of fluid metal will bring it quickly into contact with cooler metal, causing it to lose most of the heat differential that it had. This will slow down if it will not stop the upward movement by itself. There is also the third factor. The ease with which convection can take place in a fluid is inversely proportional to its viscosity. Fluid iron and nickel are incredibly more viscous than water. One can therefore presume that any convection within the Earth is very slow. The gravitational action of the moon has an observable effect on the Earth's fluid core. We see the effect in the tides. It happens all the time. The effect on the Moon is to slow it down in its orbit. The energy taken from the Moon is converted into heat within the Earth. Heating of the upper and more fluid part of the Earth's core is likely to hinder if not almost stop convection altogether. The only evidence that we have about the Earth's inner workings has been derived from seismology. This shows that earthquake waves travel trough the Earth in two ways. The two ways that earthquakes are detected in remote locations provide an indication that the Earth's inner core is solid and the outer core is fluid. The only evidence that there is some form of convection within the Earth is through plate tectonics. Europe is moving away from North America at the rate of fractions of an inch per year. This evidence for convection shows that it is very sluggish and probably unlikely to provide enough movement of electrically conducting material to cause more than the slightest effect on a magnetic field.

The Earth's Rotation and the Solar Wind
I have failed to find a satisfying reference to the interaction between the plasma in the solar wind and the Earth's rotation. Let us assume for a moment that the Earth is a sphere in a static fluid. As the sphere rotates, the fluid in contact with the sphere will rotate with it. If the fluid is an electrical conductor, very little will happen because an equal number of moving negatively and positively charged ions will produce mutually cancelling currents. If the fluid is ionised in a particular way, a circular current will form around the sphere.

The Displacement of the Earth's Magnetic Poles
The solar wind is an ionised plasma that radiates more or less uniformly outwards from the sun, so the circular movement of ionised plasma caused by the Earth's rotation will create a magnetic field roughly in line with the Earth's rotation axis. It will be displaced towards the Earth on its sunlit side and away from the Earth on its dark side. This effect has been observed by spacecraft. If the Earth was not moving around its orbit in a plasma field, and did not have an axial tilt, the current caused by the circular movement of plasma would produce a magnetic field in line with the Earth's axis. As this is not the case, the solar wind speed, the Earth's tilt and the Earth's orbital progress, can account for the offset of the magnetic axis from the axis of rotation.

The Displacement of the Magnetic Poles of the Earth and Other Planets
The distribution of the iron and nickel in the Earth's core may well affect the positions of the magnetic poles. However, when the magnetic fields of some of the gas planets are considered, comparable differences between spin and magnetic axes are observed. The axis of the Earth's magnetic field is not noticeably affected by the position of the Moon as it orbits the Earth yet the tides clearly show how the Earth is distorted by the Moon's gravity. Because the mass of the Earth's molten metallic core is the major part of the Earth's mass, it must be affected by the moon like the tides, but the effect is hardly noticeable in the positions of the magnetic poles. The Sun's gravity has a lesser effect on the tides than the Moon's. Since the Moon has little effect on the positions of the magnetic poles, the Sun's gravitational effect must be even less. It therefore cannot account for the displacement between the magnetic axis and the rotational axis of the Earth.

The Iron Dynamo Theory Applied to the Gas Planets
I cannot prove that the iron dynamo theory is wrong directly but I cannot find an electrical analogue to support it. The iron dynamo theory does not seem to fit with the magnetic fields of the gas planets. None of the gas planets contain much iron, and liquid iron is very much less magnetic than the solid element. Dynamo theorists happily substitute hydrogen for iron in the gas planets but, as the gyroscope analogue shows, a spinning magnetic material does not generate a magnetic field. I have not been able to trace a report of research done on the ability of circulating liquid hydrogen to generate a magnetic field.

Solar Wind, Atmosphere and Rotation
Jupiter has a high rotational speed, a large diameter and an extensive atmosphere. These factors tend to indicate that the rotational interaction between the atmosphere and the solar wind is largely if not wholly responsible for its magnetic field. The magnetic fields of the other planets are observed to be roughly in proportion to their equatorial rotational speeds, their diameters and the densities of their atmospheres. The internal convective conductive fluid dynamo theory seems to have no relationship with the sizes, densities, compositions and tilts of the various planets and their magnetic fields.

Uranus and Its Magnetic Field
The internal dynamo theory starts to become untenable when one looks at the magnetic field of Uranus. Its axis of rotation is tilted at 98 degrees with respect to its orbital axis, and its magnetic axis is tilted at 58 degrees with respect to its rotational axis. The orbits of the moons of Uranus and its ring are in line with its equator. Any influence that they might have on the magnetic field would be to make it align with the spin axis. Because the magnetic axis is so far out of line with the spin axis, it must be concluded that the magnetic field is largely if not wholly produced by the interaction of the outer atmosphere and the solar wind.

Electronic Fluids, Plasmas and Magnetism
The movements of an ordinary fluid are fairly chaotic, but if the fluid is ionised, its movement is constrained by the magnetic field that it produces. In electronics it is routine to produce and control ionised fluids with high precision. Evidence for this is can be seen on the screen of any television set or computer monitor that uses a cathode ray tube.. Cathode ray tubes in televisions and monitors make use of magnetic fields to control and deflect electron beams. An electron beam creates its own magnetic field that interacts with the magnetic fields produced by the coils around the tube.

A wire carrying an electric current produces a circular magnetic field around itself. The field strength is proportional to the current. An electron beam has similar properties but its magnetic field also increases with speed. Electrons typically travel in wires at around 6.5kph although their effect travels at around 90% of the speed of light in vacuum. (Compare electrons in a wire with water in a long pipe that is already filled with water. Put in a litre of water in one end of the pipe and almost immediately a litre comes out of the other end - but it is not the same litre.)

Electrons in a beam produce an average cylindrical magnetic field that interacts with the magnetic fields of the individual electrons. An electron with a path that is divergent with respect to average path is constrained by the average magnetic field. The average magnetic field acts like a sort of pipe that keeps the electron within its walls. The strength of the average magnetic field is proportional to the current and the speed of the electron beam. The constrictive effect of the average magnetic field on individual electrons increases as the strength of the magnetic field increases. The result is that an electron beam tends to become narrower as it goes faster.

Electric currents in other plasmas create similar magnetic fields and behave in a similar manner. Lightning and decorative displays that produce lightning effects inside a tube or sphere show this to be true. The illuminated tracks are always very narrow.

An electron beam is one type of plasma. The solar wind is a plasma that is largely made up of protons that are physically much heavier than electrons and carry a similar but opposite electrical charge. The current carried by protons also increases with speed and the constriction produced by the magnetic field they generate increases proportionately. The average solar wind speed is around 600km/s but it can rise to around 2000 km/s or more during solar flares. The particles in the solar wind mix with and are rotated by the earth's outer atmosphere, generating a ring current around the Earth. This creates a bar magnet type of magnetic field which is roughly in line with the axis of rotation of the Earth. The magnetic field assists in the deflection of protons in the direction of the Earth's rotation. In the same way as an electron beam's magnetic field constricts the paths of the individual electrons in the beam, the magnetic field caused by the ring current constricts the paths of the protons that create the ring current in the first place. Countless trillions of separate proton streams form the solar wind that strikes the Earth's outer atmosphere. The magnetic fields of these proton streams oppose the ring field on the dawn side and are repelled, but are attracted to and add to the ring field near the sunset terminator. Electric currents and magnetic fields are always at right angles to each other. Moving ionised particles cannot cross magnetic fields without being deflected and never move parallel to them. In consequence the magnetic field around the Earth acts as a radiation shield against charged particles on the sunward side.

Solar Flares and Their Effects on Earth
When solar flares occur, the intensity and speed of the solar wind increases dramatically. Approximately 21.5 hours after a solar flare has occurred, the increase in speed and intensity arrives at the Earth's orbit. A very rapid increase in the ring current occurs with a corresponding increase in magnetic field strength. At the north magnetic pole between northern Canada and Greenland, the magnetic field is nearly vertical with respect to the Earth's surface. A large and rapid change in the field will induce currents in conductors at right angles to the field. The most affected conductors are the power lines of the Canadian electricity grid which are parallel to the Earth's surface. The power surges in the grid can cause problems ranging from temporary shutdowns to severe damage to the transformers and switchgear.
If the circulating iron theory for the Earth's magnetic field was correct, the effects of solar flares would be less than they are. The theory implies that most of the Earth's magnetism is derived from circulating iron and not the solar wind. Changes in the strength of the solar wind should thus have only a marginal effect on the Earth's magnetism. The evidence indicates that changes in the strength of the solar wind have a large effect. One must therefore presume that the circulating iron theory cannot account for more than a small proportion of the Earth's magnetism.

The parts of the Earth that are least protected from ionising particles are around the magnetic poles where the higher strength magnetic field is nearer the Earth's surface. The ionised particles can penetrate to a lower altitude and excite the gases in the upper atmosphere so that they glow visibly creating the aurorae. The aurorae are bigger and brighter just after a solar flare has occurred.

Magnetic Field Reversals
Geologists have found that the earth's magnetic field has reversed from time to time during the geological past. The circulating iron theory requires a mechanical contrivance to reverse its direction. Geologists have detected nothing that would indicate that the Earth has changed its direction of rotation at any time in the past. One must therefore presume that a very strange and generally harmless process has caused the circulating iron to change direction. What physical law could account for such behaviour? Newton's laws of motion apply. What force could re-route the incredibly massive iron circulation within the Earth without affecting the Earth's surface? Such a force has not yet been conceived even in science fiction. A force field that did not affect a planet's surface but could apply billions of tons of pressure 1000 km below a planet's surface would be regarded as silly by most science fiction readers

At present the solar wind consists of predominantly positively charged particles. Protons have sufficient mass to be able to travel continually outwards from the sun once they have achieved the speed of escape from the sun. Isolated electrons have a similar but negative charge and virtually no mass. Electrons quickly change direction when they encounter magnetic fields so they are generally unable to travel far from the sun on their own as protons can do. However, even a body as large as the sun cannot lose protons indefinitely. Sooner or later the sun will build up an extremely large negative charge because of proton depletion. This will attenuate and eventually stop the emission of protons. What happens next would normally be unpredictable. However, the geological evidence indicates that the Earth's magnetic field reverses from time to time. This could mean that the sun starts to emit negatively charged particles, (atoms with extra electrons attached) creating a negative solar wind. If the rotation of the Earth's atmosphere interacting with the solar wind is responsible for the Earth's magnetic field, the magnetic field polarity will change as the solar wind polarity changes. From the Earth's point of view, such a change in the electrical polarity of the solar wind would have relatively few harmful effects. The fading out of a positive solar wind and a subsequent replacement by a negative solar wind would leave the Earth without a magnetic field for a time. The author is not aware of any reports of extinctions associated with changes in the Earth's magnetic field that are comparable to those at the Cretaceous/Tertiary boundary. The change from a positive to a negative solar wind and back again is based on the laws of electrostatics. There are no laws governing a repeated change of direction in an iron dynamo.

Magnetic Fields, Planetary Rotations and Atmospheres
If the Earth is excluded from consideration, the magnetic fields of the Solar System planets seem to correspond with two factors - the amount of atmosphere and the equatorial rotational speed. If either rotation or atmosphere are absent, there is no magnetic field. If the equatorial speed is high and atmosphere is plentiful, there is an enormous magnetic field. Jupiter, Saturn, Uranus and Neptune have little iron or any other magnetic elements to create a magnetic field with, yet they all have strong magnetic fields. The dynamo theory substitutes hydrogen for iron in these planets but offers no satisfactory explanation for the differences between their axes of rotation and magnetic fields.

The amount of atmosphere a planet has is related to the escape velocity. Other factors also have an effect. These include the surface temperature and the molecular weights of the gases concerned. The effective angle of incidence of the solar wind on a planet is a function of three speeds and the tilt of a planet's rotational axis. The first is the outward speed of the solar wind. The second is the orbital speed of the planet. The third is the rotational speed around the planet's equator. Perhaps some mathematician could derive an equation which would give the angle of the magnetic axis of a planet from these factors and compare the result with the observed figure.

Emulating the Solar Wind's Effect on a Planet
A method to estimate the Solar Wind's Effect on a Planet would be to construct a sort of Orrery that reproduces the orbit, rotation and tilt of each of the planets in turn. The axis of the Orrery is set in the middle of a circular pond filled with salt water. An electrode representing the sun is placed under water at the centre of the pond and an annular sheet electrode is placed under water around the periphery of the pond. A rough-surfaced, non-conducting ball, controlled by the orrery, and held under water, represents the planet. The orrery is then set in motion and a check for the presence of a magnetic field around the ball is made. It is unlikely that a magnetic field would be detected under these conditions. The pond electrodes are now connected to a battery and the experiment is repeated. A magnetic field will be detected around the ball. If the experiment is conducted on a large enough scale, it should be possible to determine the axis of the magnetic field of the simulated planet. If the results of this experiment are similar to the observed magnetic fields of the real planets, it must be concluded that the solar wind is the major factor in the creation of a planet's magnetic field.

An Experiment to Emulate an Iron Dynamo
A related experiment requires a large, non-conducting ball filled with a mixture of salt water and laser toner. [Most laser toners consist of iron dust, carbon black and a plastic binder. The ideal toner for this experiment should remain in neutral suspension in the salt water.] A spherical heater is placed at the centre of the ball. Cooling fans are arranged around the ball. The ball is rotated and observations are made to see if a magnetic field is generated. In this experiment the salt water provides the electrical conductivity and the iron dust provides the magnetic element required for the iron dynamo theory. The heating, cooling and rotational speed should be adjusted to produce a detectable magnetic field. If the heater starts to boil the water before any magnetism is detected, the iron dynamo theory will have received a severe setback.

Attempts to Calculate the Magnetic Field Strengths of the Solar System Planets
The following table shows a possible relationship between an estimated magnetic field strength and known planetary factors. The calculations are based on two factors. The presumed magnetism for each planet is based on the escape velocity multiplied by the speed of rotation. The figures for Magnetism 1 ? have been normalised to give a figure of 1 for the Earth. Decimal points have been aligned with the addition of zeros to make figures from different sources consistent. The assumptions have been based on the fact that the amount of atmosphere a planet has is related to its escape velocity. The current generated by the outer atmosphere is in proportion to the speed at which the planet rotates. The magnetism generated is the result of that current. The figures for observed magnetism in the bottom line are taken from a table in the book Astronomy Today.1

Property\Planet

Mercury

Venus

Earth

Mars

Jupiter

Saturn

Uranus

Neptune
Day in Hrs

1408.800

5832.000

24.000

24.620

9.830

10.230

10.800

15.800

Escape Velocity

4.280

10.300

11.200

5.000

59.500

35.600

21.220

23.600

EV/Day

0.003

0.002

0.467

0.203

6.053

3.480

1.965

1.494

Magnetism 1 ?

0.007

0.004

1.000

0.435

12.970

7.457

4.210

3.200

Magnetism 2 ?      0.0009       0.006   1.000   0.032    6.890   0.311    0.024      0.011
Magnetism A.T.

0.011

0.001

1.000

0.001

13.890

0.670

0.740

0.430

The observed figures for magnetism in Astronomy Today.(shown as A.T.) quoted for Saturn, Uranus and Neptune are presumably based on Voyager data, and the figure for Mercury is from Mariner data. The rough and ready way of deriving a figure for the magnetism of each planet in Magnetism 1 ? seems to have some relationship to the observed data. A different formula for the calculation of the relative amount of affected atmosphere might well bring the estimated magnetism closer to the observed figures. A plasma torus exists along Io's orbit. This may add to or subtract from the calculated figure for Jupiter in the table. The high estimated figure for Mars may be due to the atmosphere being very much less dense than the escape velocity figure indicates. Mars apparently had liquid water once but there is none now. The same applies to the atmosphere - there is hardly any left. Another factor in addition to the escape velocity must account for the observed lack of atmosphere and consequently the observed lack of magnetism.

New Figures 10th June 2005
The Magnetism 2 ? figures were derived by a different method from the Magnetism 1 ? figures. They still do not match the Astronomy Today figures but they bear a slightly closer relationship than the earlier figures. One thing that was noted during the recalculation was that the velocity of the solar wind does not change much from Mercury to Neptune. There is roughly a 0.5% drop in speed. This is because the rate of change in the sun's gravity is diminished to a low level at Mercury's orbit.
As Newton worked out, gravity declines with the inverse square of the distance. At 2 diameters away from the sun the gravity is a quarter that near the surface. At 10 diameters distance the gravity is down to one hundredth the surface level. Mercury is 42 diameters distant, Venus is 78 diameters distant and the Earth is 107 diameters distant. As the sun's gravity gets progressively weaker, the deceleration rate of the solar wind decreases. I could not work out why some early results in the new calculations seemed to give almost the same answers for all the planets out to Neptune. I then tried iteration starting at the sun and working outwards in steps, calculating the gravity at each step, the consequent deceleration rate and the resultant speed of the solar wind. Neptune is 3235 solar diameters away from the sun. The solar gravity at Neptune's mean orbit is therefore almost negligible. The deceleration of the solar wind velocity is is comparably small.
The new figures are based on the mean proton density at the Earth's orbit - 5 per cc. I have assumed that the proton density follows the inverse square law to derive proton densities for the orbits of the other planets. The intermediate figures produced were multiplied by each planet's speed of escape to give the new results. Factors that I have not considered may make the latest figures better or worse but they cannot make a significant enough difference to weaken my theory that almost all planetary magnetism is a function of the solar wind, planetary rotation and planetary atmosphere.

The suppositions and calculations made in this essay have been based on observed data where possible. I have not yet been able to find comparable data that would support the "iron dynamo" theory of planetary magnetism. Note that my calculations are based on observed DATA. The astronomers questioned on the subject have generally taken the iron dynamo theory as read. However, none has so far been able to offer any explanation based on observed data that would support the theory except the fact that most planets have magnetic fields.

A Summary
The electronics literature treats magnetism as an effect produced by an electric current. A magnetic field that has been thus produced can be used to create permanent magnets in a range of iron, nickel and cobalt alloys. However, planetary magnetic fields are not permanent, and, in the case of the Earth, the iron in question is hotter than its Curie point. (The Curie point is the temperature at which magnetic effects in ferromagnetic materials disappear.) The interaction between a rotating planet's atmosphere and the solar wind produces a ring current around the planet. The ring current produces a magnetic field. This fact is not in dispute. The question is: are the ring currents thus produced strong enough to account for the magnetic fields that have been observed? The table of calculations and the manner in which they were derived tends to support the proposition that ring currents account for almost all the planetary magnetic fields observed so far.

The Earth's Magnetic Field Reversals
The possibility that the charge polarity of the solar wind reverses from time to time seems much more likely than a periodic reconfiguration of an iron dynamo. The geologic record includes a very large number of magnetic field reversals that are not apparently accompanied by catastrophic effects. If the iron dynamo was largely responsible for the Earth's magnetic field, the Earth would have had no magnetic protection from an ionised solar wind during the changeover period. Attempts are being made to discover if minor changes to life on Earth occurred during the absences of a terrestrial magnetic field. No records of major changes have been found so far. The Earth would need far less protection from the electrically neutral solar wind that would occur as the solar wind changed polarity. The iron dynamo theory does not offer any explanation of what would happen on Earth if the magnetic field was absent and the solar wind was still electrically polarised.

A Myth Exposed
I have repeatedly encountered references to "lines of force" (or just "lines") in descriptions of the effects of magnetism concerning the Earth's magnetic field. I think that the idea that such lines exist must be due to the way the pattern of a magnetic field is shown by using a sheet of paper laid over a bar magnet and sprinkled with iron filings. The iron filings just show the field orientation and nothing more. If there was significant force in the lines, the iron filings would be dragged either along the lines or towards the body of the magnet. In general, the iron filings do not move much. They align themselves with the field, and, because they are effectively small induced magnets, adjacent filings have the same magnetic polarity and are therefore mutually repulsive. This repulsion causes the line effect seen with iron filings. The lines are an artifact caused by the mutual attraction of strings of filings in line with the field and the mutual repulsion of such strings of filings. If the pattern produced by iron filings is photographed, the pattern can be compared with the same experiment repeated with freshly demagnetised iron filings and photographed again. If this is done repeatedly, it will soon become clear that the lines seen in the iron filings are seldom, if ever, in the same places. If the series of photographs is combined, no lines can be seen because the positions of the lines are different in each photo. In other words, there are no lines in a magnetic field.
There are no comparable references in the literature to lines of gravity or electrostatic forces yet the three phenomena are similar but different forms of stress in spacetime. If there are no magnetic lines of force, all explanations of magnetic fields in terms of such lines have no meaning.

There are also many references to charged particles moving along magnetic lines of force. How easy is it for a physical entity to proceed along an imaginary concept?

The Interactions Between Intersecting Magnetic Fields
A moving charged particle is an electric current that creates a cylindrical magnetic field around itself. The magnetic field is always at right angles to the path of the current. In the case of a current carrying particle that encounters a strong magnetic field, the particle's path is deflected until its own magnetic field aligns with the other magnetic field. Television set cathode ray tubes and electric motors rely on this basic principle. A stream of charged particles may be so energetic that its magnetic field is much stronger than the other magnetic field. When this happens, the other magnetic field is distorted to align with the stream's magnetic field. When the magnetic fields are of comparable strengths, the resultant field is shaped in accordance with the proportions of the strengths of the two fields.

An Experiment to Show the Visible Effect of a Magnetic Field
An experiment to see the effect of the interaction between a plasma current and a magnet can be carried out with a monochrome TV set or monochrome computer monitor and a bar magnet. (This only applies to screens that use glass cathode ray tubes.)

It is best to have a stationary image on the screen to see the effects. One pole of the bar magnet is moved towards the centre of the screen. The image will rotate in proportion to the strength and proximity of the bar magnet. If the experiment is repeated with the other pole of the bar magnet, the image rotates in the opposite direction. The north-seeking pole of the magnet causes a clockwise rotation of the image.

This experiment will demonstrate that the electrons in the beam will align their magnetic fields with the bar magnet's magnetic field. In so doing, their paths are altered to suit. This experiment also shows that the predominant current around the Earth must be produced by protons if the current is responsible for the Earth's magnetic field. The Earth's North Magnetic Pole has the polarity of what would a south pole of a bar magnet because it attracts the north poles of bar magnets. Because the north-seeking pole of a bar magnet rotates an electron beam clockwise, and the Earth's rotation is effectively clockwise as seen from the South Pole, the circulating current that produces a south-seeking magnetic pole at the North Pole must be positive and composed of protons.

DO NOT TRY THE FOREGOING EXPERIMENT WITH A COLOUR TV OR MONITOR

A colour TV or monitor CRT screen has a perforated steel plate behind it to align the red, green and blue electron beams with the appropriate phosphor dots. If the steel plate becomes magnetised, the colour purity of the screen may be irretrievably ruined. Never put a magnet near to a colour TV or monitor screen.

References
I have deliberately avoided using a lot of references because it would be hard to keep the list short enough to be useful and meaningful. Summaries of the present state of received wisdom concerning the solar wind and the Earth's magnetism can be found in Astronomy Today 3rd Edition by Chaisson and McMillan published by Prentice Hall, New Jersey, USA. Copyright date 1999. ISBN 0-13-080100-3.

Other background information has been gained from the Encyclopedia Britannica and the Cambridge Encyclopædia of Astronomy ISBN-0-224-01418-8. The Cambridge Encyclopædia of Astronomy is very old now as it was published in 1977. However, since later books quote the iron dynamo theory almost word for word, it is clear that all reseach on the subject has been on the basis of just finding out what someone else wrote previously (hence the quotation from Galileo).

Additional notes.
The behaviour of electrons in a cathode ray tube (CRT) can demonstrate that many alleged behaviours of ionised gases- as described in books on astronomy are just plain wrong.

The electron beam in a CRT is projected towards the viewer. En route to the screen it is deflected sideways and up and down. A television tube uses magnetic fields to deflect the electron beam. The magnetic field that deflects the beam sideways is created by a pair of coils above and below the neck of the CRT. The sideways deflection creates the lines that make up the picture. A further pair of coils mounted on either side of the neck of the CRT provides the vertical deflection necessary to create what is known as a raster of lines.

From this it can be seen that a vertical magnetic field deflects electrons sideways and a horizontal magnetic field deflects electrons vertically. At no time do the electrons move along "magnetic lines of force" as claimed in many astronomical sources.
One must not forget that magnetic lines of force are an imaginary concept.
(They are no more real than contour lines on a map.) What applies to electrons applies equally to streams of positively ionised gases. Positively ionised gases move in the opposite direction to electrons but the rule is the same: a vertical field causes lateral deflection.

The behaviour of electrons and protons is different because protons are 1,800 times more massive than electrons. A magnetic field that can deflect an electron stream through 70 or 80 degrees can only deflect a comparable proton stream through less than one degree. Since the space between the sun and Earth is filled with magnetic fields, an electron emitted from the sun is not likely to get very far but a proton could well travel all the way to Earth almost unhindered. An atom that is negatively charged will be deflected in inverse proportion to its mass.

Since the sun is currently emitting protons towards the Earth, the Earth must be gradually accumulating a positive charge with respect to the sun. At the same time the sun must be gradually accumulating a negative charge. At some point the negative charge on the sun will restrict the emission of protons and the positive charge on the Earth will attract negatively charged particles.

Using a Computer Simulation
I have heard of a computer simulation that is claimed to have shown the earth's magnetic field reversals. Since it must be an iterative program, the same code is used repeatedly. Such a program must follow the standard way numbers are represented in computers. That is to say that the most significant bit (MSB) of a number is a 1 if it is negative and a 0 if it is positive. How likely or unlikely is it that the MSB is accidentally changed by a glitch in a very long running iterative program? If such a glitch occurred, it would give the result of a reversal of the Earth's magnetic field. In my opinion, such a computer simulation would be aimed at proving an existing hypothesis and not to disprove it. Science is littered with examples of experiments where the results were cooked or carefully selected to give the desired answers. I think that the computer simulation of the Earth's magnetic field is one of these.

Update 07/03/04
Email Correspondence

After very many attempts to get a response from astronomers about how they arrive at their ideas about magnetism, I have had an email correspondence with Loren Acton who is a professor of astronomy. The exchange of emails has led to a deeper analysis of the foundations of astromomers' magnetism. As a result some basic factors have emerged. Astronomers have interpreted Maxwell's equations to indicate that electricity and magnetism are interchangeable. This led Harold and Horace Babcock to derive hypotheses about the sun's magnetism which underlie what I call "astronomers' magnetism". This assumes that both the Sun and the Earth produce magnetism in the same way. In each case it seems that a variation on the iron dynamo theory applies.

After looking at a website http://www.phy6.org/earthmag/dynamos2.htm which describes this theory in more detail, I have found that it relies on a misconception of the way electricity and magnetism relate to each other. It is claimed that the Earth's rotation in the magnetic field (generated by the electric currents flowing within the Earth) causes currents to flow that generate the magnetic field in the first place. When I read this I knew there was something fundamentally wrong with this concept but I could not put my finger on it. Then, when I turned it inside out, I had an answer.

Quote:
"So the molten metal is believed to be circulating. By moving through the existing magnetic field, it creates a system of electric currents, spread out through the core, somewhat like Faraday's disk dynamo, discussed earlier. Currents create a magnetic field--a distribution of magnetic forces--and the essence of the self-sustaining dynamo problem is to find solutions such that the resulting magnetic field is also the input field required for generating the current in the first place."
An Extended Explanation Concerning the Faraday Disk Dynamo

A Relatively Non-technical Explanation of Electric Motors and Dynamos.
A dynamo and a motor are two more or less equal but opposite applications of the same principles. The way electric motors work is very well known so it is possible to use this knowledge to show the relationship between an inducing current and an induced current. A D.C. electric motor has a rotating part called an armature. This is wound with coils that have a very low electrical resistance. The connections to the armature are via a series of contacts called a commutator and a pair of sliding contacts called brushes. This connection arrangement ensures that the magnetic field produced by the windings around the armature is always in the same direction as the armature rotates. Motors that use this connection system are universal. They are used extensively in cars to operate the heater fan, the starter motor, the windows, and the door locks. In the home the same sort of motor is used in vacuum cleaners. In all cases the motor prevents itself from being burned out by preventing an excessive current flowing through the armature windings. This is because the motor, when it turns, generates a voltage that opposes the input voltage.

A D.C. Motor Example
Let us take the motor that drives the heater fan in a car as an example. The car's battery voltage is 12 volts. The resistance of the armature windings is around 1/10 of an ohm. If the armature was held stationary while the motor was switched on, a current of around 120 amps would flow through the armature windings. (Voltage (Volts) divided by resistance (Ohms) = current (Amps). 12/0.1 = 120) The wire used to wind the armature is around the same thickness as 15 amp fuse wire. If the armature remained stationary, it would burn out in a fraction of a second. As we all know, this does not happen most of the time so something must stop this from happening. What happens is that the motor also acts as a dynamo when it turns and generates an opposing voltage that is close to the input voltage. A car heater fan normally draws around 4 amps when it is running. In this case the motor generates a voltage like a dynamo of minus 11.6 volts. This leaves 0.4 volts to turn the armature. It might not seem much but it is enough. As the armature has a resistance of 0.1 ohms, the current drawn is 4 amps.(0.4/0.1 = 4) The power consumption is around the same as a car headlamp bulb at 48 watts. (Watts = Voltage times Current. 12 times 4 = 48) We usually treat the motor as an entity without bothering about what goes on inside it.


A Dynamo Example
Now we can look at the opposite of a motor which is a dynamo. With a motor we use electrical energy to produce mechanical energy. With a dynamo we use mechanical energy to produce electrical energy. The layout for motors and dynamos is the same. Both use a fixed magnet stator and a wound armature rotor. A dynamo is a machine for producing direct current or D.C. The fixed magnets for either can be permanent magnets or temporary magnets energised with electricity. Most electric motors and dynamos use electrically energised fixed magnets. The dynamos used in older cars during the 1950s relied on what is known as residual magnetism. That means the very small amount of magnetism left behind when a temporary magnet is no longer energised with electricity. The way one of these old dynamos was wired used this very small amount of magnetism to generate a small amount of electricity to power the temporary magnets. This made the magnets stronger so that more electricity could be generated. In this way a dynamo could quickly generate enough power to charge the car's battery and run the car's electrical services.

Comparing a Basic Dynamo With the Earth's "Iron Dynamo"
The basic dynamo is made in two parts. These are the rotating armature and the fixed magnets. Note that the fixed magnets of a dynamo are separate from the armature and can therefore be connected to be of either polarity. The "Iron Dynamo" alleged to be in the Earth consists of just moving liquid iron which acts as an armature that is supposed to produce a current which creates a magnetic field which in turn causes the "armature" to generate the current.
It might be simpler to visualise a dynamo and a motor coupled together. The motor turns the dynamo which generates the electricity to drive the motor. If this arrangement could work we would have a perpetual motion machine. In practice, both motors and dynamos have an efficiency of around 50%. The electrical energy produced by a typical dynamo is around half of the mechanical energy used to turn it. The mechanical energy produced by a typical DC motor is around half of the electrical energy that drives it.
Note: A bicycle "dynamo" is not a dynamo at all. It is an alternator. Its output is AC. Proper dynamos only generate DC.

The dynamo in the dynamo theory that is used to explain the Earth's magnetism has only one part. It is the molten moving metal around the Earth's core. Its rotating part and its magnet are fixed together and the electrical connections are fixed in the opposite way to those which are used in the basic car dynamo. The connections are the same as for a basic car dynamo's fixed temporary magnet in reverse. That is to say, any current generated is effectively used to destroy any magnetism that might be there in the first place.

Conclusion about the Earth's and Suns's Dynamos
A self sustaining magnetic field that is generated by the current that it induces cannot exist. The current that produces the magnet would be opposed by the current induced by the magnet. Therefore the iron dynamo theory is based on a misunderstanding of basic electrical theory.

An Update - 8th March 2004
After coming to the conclusion that the Earth's and Sun's internal dynamos could not work for the reasons described, I thought that I would dig out one of my old physics books to see if it could provide any more information about the relationship between magnetic fields and induction. I soon discovered that I had floundered my own way to describing Lenz's Law.

Lenz's Law
"The direction of the induced E.M.F. is such that the current which it causes to flow (or would flow in a closed circuit) opposes the change which is producing it."

For the less technical readers the term E.M.F. means Electro Motive Force. In practice it means the voltage. In electrics a closed circuit is one where there is a continuous connection from start to finish. An open circuit is one where there is a break in the circuit like a switch in the off position.

The dynamo theory as explained in many descriptions contradicts Lenz's Law and is therefore invalid.

The Electric Motor and Lenz's Law
Now, let us assume that the motor mentioned earlier is 50% efficient. That means 50% of the power used just turns the motor and 50% is converted to mechanical power to operate the fan. So, if the fan is removed, half the power used would be saved. This means that the motor would only use 2 amps. The motor would spin faster to generate a reverse voltage of 11.8 volts. The next question would be - how efficient would the motor have to be if it only used 2 amps with the fan attached? The answer would be 100% efficient because we have seen that having the fan on the motor consumes 2 amps more than if it is not attached. So the 100% efficient motor would generate 12 volts to oppose the 12 volt input. It would consume no power. Now think of the Earth as a motor that needs no power to make it spin. It will more or less behave as the 100% efficient motor. It would generate the equivalent voltage of its apparent input voltage derived from the magnetic field around the Earth. It would effectively cancel the magnetic field that was there in the first place. This is an example of Lenz's Law in action.

Dynamos and Alternators  
In modern cars an alternator is used instead of a dynamo. A dynamo uses a commutator to make the output D.C. A car's alternator is a bit like a dynamo inside out. The "fixed magnets" rotate inside and the outside part is stationary. The output is alternating current or A.C. Semiconductor diodes rectify the A.C to produce the D.C. needed by the car's services. The electrically energised rotating magnets do not consume much power so they can be supplied via a pair of sliding contacts called slip rings. The older dynamo had to supply all the electrical power via its commutator - a sliding contact system. There are no sliding contacts for the output of an alternator. The alternator system is much more efficient but it is only made possible because of the availability of semiconductor diodes of sufficient robustness to carry the currents used. These diodes only became available in the late 1960s. A typical dynamo as used in old cars would supply 17 amps. A modern alternator can supply 50 amps or more.

New Topic 10th June 2005.
In response to an email asking about the strength of the Earth's magnetic field and if it contacts the Earth I wrote:
The magnetic field of the Earth is similar to that of a bar magnet in some ways. That is to say that the magnetic field is concentrated and vertical at the poles where it intersects the Earth's surface. At the equator the field is horizontal.
The orientation of the magnetic field is three dimensional. A conventional compass gives only the lateral orientation. The vertical component can only be checked with a perfectly balanced steel rod that is balanced when unmagnetised and subsequently magnetised. The rod will take up an orientation that shows the angle of the local prevailing field in the horizontal and vertical. The field strength varies with distance from the Earth's centre more or less in the same way as a bar magnet. It diminishes with the square of the distance from the Earth's centre.
The Earth's magnetic field is not uniform because it is mainly if not wholly caused by the interaction of the solar wind and the Earth's atmosphere. It is compressed on the sunward side and extended almost into a teardrop shape on the dark side.
The magnetic field of Jupiter is similar in shape but very much stronger.

A Further Thought for Astronauts 10th June 2005
It is claimed that the Earth's magnetic field shields us from a lot of radiation in the form of particles from the sun and the rest of the universe. If a large coil of wire carrying a small electric current was wrapped around the parts of a space ship or a space station occupied by humans, it could create a magnetic shield comparable to the Earth's magnetic field. The field strength would have to be much greater than that of the Earth because it would have to be physically very much smaller. The current in the coil can be increased to cope with solar flares. The snags with a magnetic shield are threefold. The magnetic field could upset the way some instruments work on a spacecraft, it would work like a magnet, attracting ferrous particles of debris left by the disintegration of earlier spacecraft, and it would give the spacecraft a tendency to rotate in the solar wind.

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Display Note
A version of this essay first appeared on this website on 10th February 2000 with the screen set to 800 x 600 mode.
This version has been rearranged to make it look better with a 1024 x 768 view. The text has been slightly revised.
Publishers that produce scientific or astronomy magazines are invited to publish this essay.
Copyright © 10th February 2000, 24th May 2002, 8th March 2004, 10th June 2005, 7th September 2005, 1st July 2006 & 22nd September 2006.

Please send your comments to me at my new email address: wilf dot james at ntlworld dot com
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Electricity and Sunspots
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Earth's Magnetism
Hubble Constant

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