Get a Straight Answer

Question #13

My question is about induced magnetism and magnetic shielding.

I understand that we can screen out magnetic fields from a region by wrapping a piece of soft iron around the region. However, I also understand that soft iron can easily receive induced magnetism when placed near a permanent magnet.

So now my question is that: How is it possible to shield a region that near a permanent magnet by using a piece of soft iron? Won't this piece of soft iron eventually get induced magnetization and have the ability to attract any magnetic material that is nearby.?

Ong

Reply

Magnetic shielding is not my speciality and you might get a better answer from an engineer familiar with magnetic design, but I will try.

Soft iron--especially the kind used in shielding (mumetal, etc.) does not take permanent magnetization. Steel does, but even there, the magnetic intensity must be high enough for that to occur.

In shielding (e.g. a video tube) you wrap a sheet of soft iron around the shielded object, and the magnetic field lines which would have closed through the interior are diverted and close through the shield instead. Therefore any magnetic field that existed in the interior is greatly weakened. The field inside the iron sheet is stronger, but that is no problem--in fact, that is what we wanted to do, take the magnetic field from the inside volume and put it elsewhere (you can't just get rid of it, for all magnetic field lines have to close somewhere).

I hope this answers your question

Question #14

I am a student working on a science fair project which deals with possible use of the solar wind in space travel. My hypothesis is that ions in solar wind can be gathered and used as propulsion for long-term spaceflights. In theory, would this work? Thank you. SEG

Reply

Something like this has been considered, but using the pressure of sunlight rather than that of the solar wind (I have not calculated it, but it seems the former is much bigger). The idea is to spread a huge sail, say of mylar with a reflecting coating (the kind that is used to darken glass walls in office building) and have it face the sun, so that sunlight bounces back. It is analogous to the way the wind pushes a sailing ship and in fact, this has been called a "solar sail." None has been tried so far. I believe there was even a story by Arthur Clark on that idea.

Question #15

I am an 8th grade science teacher in Texas. I am trying to find out if anyone has ever tried to make a working model of a sphere capable of generating a magnetosphere. I feel that the testing of such a model in space could provide some insight into geologically problems such as why the earth's magnetic field periodically reverses itself. Please let me know if anyone has ever made such a model to test in space and what has been learned from such models. Thank you -- Jim

Reply

Your short questions requires a very long answer!

Briefly: Yes, people have devised working models of the magneto- sphere, but while such models have provided clues on magnetic fields in space, they tell nothing about reversals of the Earth's field. For that you have to probe the inside of the Earth, on which whatever happens in space has little effect. However, there also exists progress in that direction.

Back to your question: The Earth's magnetism affects surrounding space in interesting ways. But surrounding space has very little effect on it--things would be just the same if the Earth were a hunk of magnetized iron. Look up under "Terrella" (in the index here) and you might see why ideas like yours are nearly 400 years old!

Question #16

Dear sir, I wonder if you could tell me exactly what the VAN ALLEN BELT is and how much radiation does it contain, i.e. how many rems of radiation are there out there?

Plus, what protection would organic life need to be protected from this radiation?

Reply

The radiation belts are regions of high-energy particles, mainly protons and electrons, held captive by the magnetic influence of the Earth. They have two main sources. A small but very intense "inner belt" (some call it "The Van Allen Belt" because it was discovered in 1958 by James Van Allen of the University of Iowa) is trapped within 4000 miles or or so of the Earth's surface. It consists mainly a high-energy protons (10-50 MeV) and is a by-product of the cosmic radiation, a thin drizzle of very fast protons and other nuclei which apparently fill all our galaxy.

In addition there exist electrons and protons (and also oxygen particles from the upper atmosphere) given moderate energies (say 1-100 keV; 1 MeV = 1000 keV) by processes inside the domain of the Earth's magnetic field. Some of these electrons produce the polar aurora ("northern lights") when they hit the upper atmosphere, but many get trapped, and among those protons and positive particles have most of the energy .

I looked up a typical satellite passing the radiation belts (elliptic orbit, altitude ranging from 200 miles to 20000 miles) and the radiation dosage per year is about 2500 rem, assuming one is shielded by 1 gr/cm-square of aluminum (about 1/8" thick plate) almost all of it while passing the inner belt. But for ourselves no danger exists. The way these particles move in the magnetic field prevents most of them from hitting the atmosphere, and the few scattered into orbits that intersect the ground, are absorbed by the atmosphere before they get very far. Even the space station would be safe, because the trapped orbits usually stop above it--any particles dipping deeper down are lost much faster than they can be replenished.

Question #17

I'm curious as to what effect the shape of a magnet has on the nature of the magnetic field patterns generated. For example, would there be any significant or even noticeable difference between a cylindrical bar magnet with fillet 'radiused' edges and one without the fillets?

Instead of your run-of-the mill bar magnet or cylindrical bar magnet with flat ends, what can be expected in a spherical magnet, an oval/oblate spheroid ('jelly bean' shape), a cylindrical bar magnet w/hemispherical divots scooped out of the ends?

Thanks, -- Rhamis

Reply

The shaping of magnetic fields is a complicated art, with formulas and computer codes. In general engineers separate the source of the magnetic field--an electromagnet or a piece of magnetized iron-- from the "pole pieces" which shape the field, which are usually made of soft iron or special alloys and are fitted to the ends of the magnet.

The virtue of soft iron is to confine the magnetic field lines inside it. So if a magnet has conical pole pieces, tapering to a sharp point, the iron will try to keep the field lines inside itself even though (as one approaches the tip) the cross section becomes smaller and smaller. When the lines finally emerge near the tip (the must emerge somewhere), they form a tight small bundle, and therefore the magnetic field is much stronger there--though in a much smaller area--than it would be in the absence of any pole pieces. Recording heads of audio and video tape recorders use such tapered poles to concentrate the magnetic field to the strength needed for writing a record.

I don't know about spherical and elliptical magnets, but formulas probably exist for them. Some intricately shaped magnetic fields are used inside research accelerators which speed up protons and electrons to very high energies, to keep the beam confined to its vacuum tube, to focus the beam's particles and to push them out of the machine onto the target area. As noted above, it is a whole science unto itself.

David Stern

Question #18

My name is Jon and I am a 6th grader. I have an invention using magnetism to prevent cars from being stolen and to keep them from bumping into each other. I tried making an electromagnet with a 9Volt battery, but it wasn't very strong. Can you tell me how to make a stronger magnet? Can I use a larger battery or real electricity? Thank you,

Reply

I don't know what your invention is, what the magnet is supposed to do. If you want it to close an electric circuit, you are essentially building a device known as a relay. You can probably get old relays from a radio repair shop, or any place which has junked electric devices (cars have relays, too). Or ask your science teacher for help.

Building electromagnets without calculating and measuring is not simple: you must match the size of the wire and its length to the source of current (manufacturers of relays do so, of course). In particular be cautious about using house current (you call it "real electricity", but anything you use is real electricity). A small battery is limited in what it can do--usually, not much. House current is backed by big power stations, which can pour a LOT of "juice" into whatever you attach. If your wire is short and thick, it will try to draw a big electric current: a battery will be unable to provide it, but the power station can and will, enough electricity to perhaps melt a wire and cause a fire, or at least blow the fuses or trip the circuit breakers which are meant to protect houses against just this.

Also, house current is backed by a relatively high "electric pressure" (voltage) and can cause a nasty shock. Finally, even if you got the magnet working on this, it would hum and jitter, because houses have an "alternating current", which goes down to zero and up again more than 100 times each second. If you ever heard an electric device humming (old fluorescent lights somethimes do), that is the reason.

So my advice--stick to batteries, get a relay (you can also disassemble it and use just its magnet, if that's what you want), and most important, read and learn. You are just at the very beginning of an interesting adventure.

David Stern

Question #19

Could a large ring of wire (or concentric rings) placed in space with current flowing through them be used to effectively focus solar energy? Would space help toward a superconductor effect such that power consumption is reduced?
  Rings of wire are cheap, if they could form a magnetic lens it could be directed to a point and harnessed...

Curious.... Mike

Reply

It wouldn't work, for several reasons, but mainly, the ring's magnetic field would only affect charged particles of the solar wind, and these carry much less energy than ordinary sunlight. A mirror is a much more efficient way of harvesting solar energy.

(Maintining the current in the ring also consumes energy, and the particles are not deflected and concentrated the way light is focused by a lens.)

Question #20

I have a question pertaining to the forecast Solar Maximum. I have heard about the upcoming Solar Maximum starting soon (CNN.com article, Nov. 11, 1999). I have also heard (unofficially), that there could be a very large solar storm near the end of April.

Finally, it is relatively commonly known that there is going to be an unusual alignment of the planets in our solar system at the beginning of May, 2000. Has there been an in-depth study to determine effects of the combination of these phenomena, and the potential impacts on both our solar system, and our planet? Could this combination of phenomena:

1. Promote a solar flare, or CME, significantly larger than previously experienced in recorded history?
     I have heard of Super flares emitting from G Class Stars, and the theory describes large planets in a close orbit (Jan. 8th Article, Sun-like stars said to emit super flares, CNN). Now, I don't expect this size of phenomena to happen here, but with the unusual planetary alignment, I do believe that this could create larger effects than normal, like a significant Solar-Magnetic Ejection, especially with the excitation of the Solar Phenomena. I'm just curious as to how much larger.

2. Disrupt the crust of our planet, creating a significant amount of tectonic activity, and if so, by how much?
     Now, I know our planets are very far apart, but if the magnetic attractions are larger than normal, and these magnetic attractions promote significant SME activity, this could promote some strange tectonic happenstance, especially with the fragility of our planet and its crust.

3. Potentially disrupt our magnetic field severely with the combination of solar magnetic and gravitational forces?

  I am aware that during our earth's geological history the magnetic poles have sometimes changed. Could this happen here with the combination of a large CME and gravitational forces?

I hope you don't mind this intrusion, I did receive these e-mail addresses through a simplistic study I conducted on the internet surrounding this conceptual theory. No calculations, or in-depth study has occurred, but I have a hunch this should be looked at more closely, and by qualified people.

Sean.

Reply

Your message made me once more appreciate the amount of misleading and loose information circulating on the web. I have spend a great deal of time and thought on creating a web site describing what is known about the magnetic field of the Earth and the Sun's effects on it, and for a real understanding, you better look there: http://www.phy6.org/Education/Intro.html

To answer your questions in brief: The solar maximum is already here. It is not an abrupt event you can date, but the crest of a wave whose width extends over at least several years. From what I have heard, the current peak is lower than expected.

No one can predict a large solar storm months ahead of time--the best we can say is that they are more frequent near the peak of the sunspot cycle. Some big ones cause little disturbance near Earth--depends on factors like the precise orientation of the interplanetary magnetic field. Planetary alignments have no effect whatsoever. [Please look up the following item below, too!]

The large planets you read about are unlike anything in the solar system --usually Jupiter-size or bigger, and very close to the star (this has to do with the method of detection--it's hard to detect distant planets).

No solar eruption has ever been found to affect the solid Earth. Their energy is too small, and almost all of it is dissipated outside the breathable atmosphere. No earthquakes follow CMEs.

I have no control over CNN. But if you seek to understand Nature, please look up my site and at sources linked or cited there!

Happy new century

Dr. David P. Stern
Goddard Space Flight Center

Question #21

In your experience, has anyone tried to correlate lineups of the sun, earth and major planets' magnetospheres with the sunspot cycles? My spare-time effort found some correlation between lineups and cycles in a number of years. My wonderment centers around the possibility that some forces of the planets when lined up, possibly relating to their magnetospheres, impact the sun's magnetosphere causing a maximum of solar activity. I've also considered the possibility that related magnetosphere effects could be the cause of previous polar reversals on the earth. Additionally, ringing of our magnetosphere might impact charged tectonic plates...but that is again another direction. Only if you have time, please comment.

A copy of this goes to a high school physics teacher working on translating these kinds of ideas into lesson plans for students - and for my daughter.

Hugo

Reply

There exists a tempting closeness between the length of the solar cycle and the orbital period of Jupiter, but I don't think the two are related. I cannot imagine any mechanism coupling the two-- especially since the Sun rotates in about 27 days, so the relative period of Jupiter going around the Sun is of that order. Furthermore, the solar wind moves with supersonic speed, which means that solar disturbances can (and do) travel downstream with it, but disturbances from a planetary magnetosphere (whatever they might be) propagate too slowly to make it back to the Sun, upstream against the flow of the solar wind. Above and beyond all these, there is always the question of energy-- the currency in which the price of any physical process must be paid. The energy required by the solar cycle is much bigger than anything planetary magnetospheres can supply.

So what causes the cycle? The Sun rotates unevenly, slower near the poles, faster near the equator, probably because of the way gas flows in it (Jupiter also has such a difference). In a magnetized hot gas, this difference deforms and amplifies the magnetic field, and there exist some general theories of the sunspot cycle based on this, although many details remain unclear. The general idea is that as the magnetic field gets amplified, it forms concentrated "ropes" which push out the hot gas, and when they reach a certain strength, gas is displaced making the ropes are light enough to float to the surface, where they are seen as sunspots.

Again, the magnetosphere is a relatively weak influence on the Earth's internal magnetism--even a big magnetic storm only reduces the surface equatorial field by 1%. Furthermore, the time scale differs--reversals happen on time scales of 0.5-1 million years, while magnetic storms have a 1-day scale or faster.

Magnetic reversals seem to be connected to the currents which circulate in the Earth's core, presumably driven by flows there, which (like flows on the Sun) get their energy from heat. The magnetic field is fairly complicated--the 2-pole structure we see (north-south poles) is dominant, but not by as much as it seems, because more complicated modes get filtered away faster by distance. Right now the 2-pole field is declining at about 5-7% per century, but the late Ed Benton has shown that the more complex parts are gaining energy, and the total sum is fairly constant. Maybe, when a reversal occurs, for a while the 2-pole part gets small and the total field is rather complex (4, 8 poles..), and later when the simple pattern re-emerges, it is reversed.

Anyway--keep studying, keep up your sense of wonderment

Dr. David P. Stern
Goddard Space Flight Center

Question #22

Air Crew Captain

Reply

I don't know where you obtained your information, but I guess you are not referring to sunlight (one kind of radiation), but to ionizing radiation--fast ions and electrons, like those emitted by radioactive substances.

The Sun does occasionally emit such radiations into space, and I have described this in a web site on solar energetic particles

http://www.phy6.org/Education/wsolpart.html

part of a much larger web site "The Exploration of the Earth's Magnetosphere", with home page at http://www.phy6.org/Education/Intro.html

In general, I would not worry about such particles. Even at the height of the 11-year sunspot cycle, they are emitted quite rarely, maybe for a few hours in the year. Furthermore, we have a double protection against them--the thickness of the atmosphere which stops all but a few (at energies which most solar eruptions do not reach), and the magnetic field of the Earth, which deflects them from middle and low latitudes. The only aircrews who might have cause to worry would be those of the Concorde, flying 15 km high or more, and only when their path passes over the polar caps. The Concorde, I believe, has radiation detectors, so even in such an event, a red light would flash and the pilot will have time to descend to lower altitudes, where the atmosphere is a sufficient shield.

David

Question #23

I am a auto mechanic and I have a simple question for you. Scientists say their are 2 holes in the atmosphere, ironically they are around the north and south pole, and they blame these holes on chlorine monoxide or refrigerants i.e. Fluorocarbons (CFC) escaping into the ozone. Wouldn't the more likely cause of the holes be the magnetic lines of flux?
  One more quick question: could there be a way of tapping into that magnetic field as an energy source?

Thank you

Peter

Reply

There do indeed exist two "holes" in the Earth's magnetic field, around the MAGNETIC poles, whose magnetic field lines go very far from Earth and afford an easy connection to the solar wind and to interplanetary plasma phenomena. On those lines we do observe "polar rain", a drizzle of fairly energetic electrons (more energy than those of the ionosphere, less than those of the usual polar aurora) which seem to come from the Sun. Also, when solar activity floods interplanetary space with energetic ions and electrons, that is where they are most likely to come down to Earth.

However, the creation and destruction of the ozone layer does not involve the magnetic field. Instead, its factors are chemistry and sunlight, and the "ozone hole" is around the geographic poles, not the magnetic ones.

The ozone layer is maintained by an equilibrium between creation of ozone by ultra-violet sunlight, and its destruction by various natural processes (this is not my field, and I do not know details, but a lot of chemistry is involved). During polar winter, the polar cap is dark and ozone is not created, just destroyed (near the pole, with just a few hours of sunlight and the sun shining at a shallow angle, ozone creation is also reduced). The observation of an "ozone hole" in recent years suggest accelerated destruction, as predicted by Rowland and Molina.

As for tapping electric currents from space, I don't think it will work, because (1) they are very spread-out, by our standards--how can you tap a current sheet 100-1000 miles wide?; and (2) between us and them lies the atmosphere, a very effective electric insulator--as is well known to power companies, which string their high-voltage cables through air without worrying about the power leaking away. Even if we knew how to tap those current sheets, we would lack the extension cords needed for reaching them.

David

Question #24

Your site states:

  The fringes of the atmosphere at these heights are strongly heated by the Sun's x-rays and ultra-violet light (and by other causes as well), causing negative electrons to be torn off atoms and leaving the remainder of the atoms as positively charged "ions".

Dave

Reply

There exist many different ways of separating ions from electrons. Some of them are used commercially--just try a web search engine on "ion sources". Of course, any ion accelerator of the many used to study elementary particles and high-energy interactions needs such a source for generating its beam, before that beam is accelerated.

Some types of radiation detectors, e.g. Geiger counters (described in "Exploration") have radiation hit gas inside a tube. Current then briefly flows across the tube--and if you think about it, it is not enough to collect negative electrons by the central wire, which is maintained at about +1000 volts. The electric circuit will not be closed unless an equal electric charge flows to the outer cyclinder, carried by positive ions.

"Ionization chambers" operate similarly but at lower voltage--they only collect the originally produced ions and electrons, creating a much smaller signal, but one which tells about the initiating particle from the ionization it produces.

The mass spectrometer is an instrument creating an ion beam and then measuring the mass of its components by bending the beam in a magnetic field. Ancient artifacts of wood or fabric are dated by measuring the amount of carbon-14 in them, a heavy isotope of carbon created by cosmic rays in the atmosphere and decaying radioactively with a lifetime of about 5730 years. At one time the amount of carbon-14 was derived by measuring its faint radioactivity, an insensitive process which required large samples. Today a tiny sample is converted into a mass spectrometer beam, and the atoms of normal carbon-12 and of radioactive carbon 14 are simply counted.

There is much more, but I hope you get the idea.

David Stern

Question #25

Thanks in advance .... Olivier.

Reply

I presume you looked at the web site "The Exploration of the Earth's Magnetosphere" at http://www.phy6.org/Education/Intro.html. Linked to the end of that site is a web copy of the article "A Brief History of Magnetospheric Physics During the Space Age," Rev Geophys.34, p. 1-31, 1996, http://www.phy6.org/Education/bh2_1.html

The above address gives the beginning of the article, which was divided into 8 sections (including references). In unit 3, "Artificial Belts and Early Studies", below Figure 3, you will find a short discussion of "Starfish" and some references. I particularly recommend the 1968 book by Wilmot Hess, and perhaps the 1965 article in Rev. Geophys. Space Phys. by Hess at all. Bill Hess was personally involved in measuring the Starfish belt (he was my boss at the time!) and has many details which might be hard to find. The article by Brown et al. (1963) is also very useful, because it is just the introduction to an entire issue of the Journal of Geophysical Research, devoted to Starfish.

You may not find there the reason for the "Starfish" experiment. The US Air Force at the time was worried about nuclear war, in which it would have to send bombers over Russia (as in the movie "Dr. Strangelove"). Someone had the idea that by exploding a hydrogen bomb at the other end of the field line, which was not defended, enough fast electrons could be produced to saturate the ionosphere at the other end to an extent which would interfere with defending radars. Legend has it that when Hans Bethe, heard about this, he pulled out a piece of paper and quickly calculated "it would work, but only for 15 minutes," which turned out about right. I was never able to confirm that story, however.

The first artificial belts were produced by the "Argus" experiment described in the same web document, at the beginning of this section. Argus also had a special issue of JGR devoted to it, referenced in the article.

The Soviet Union has detonated some very large hydrogen bombs in space, and the book by Hess has dates and some graphs. It was their luck that those explosions were near Novaya Zemlya, where magnetic field lines are long and trapping does not last: they were gone in about 2 weeks. The US chose a near-equatorial site, on field lines where trapping is very stable, and the artificial belts lasted into the next solar maximum, damaging satellites and raising concerns.

Sincerely

David

Question #26

I teach 9th grade Earth Science and my class would appreciate the answer to the following question. What is the effect of the magnetic reversals of the poles on the migratory paths of sea turtles and certain birds and fish?

Thank you..... Janet

Reply

I have no idea how to answer your question. How could one find out? The last reversal was 700,000 years ago!

I heard that some bacteria, suspended in water, find the "down" direction using magnetic materials embedded in their bodies. When they are moved to the opposite hemisphere, they tend to orient themselves in the opposite direction. That's as far as I know

Question #27

I'm a teacher from Sweden. I'm also studying science and I have a question that I would like to ask you, about magnetism. I found your e-mail at http://www.phy6.org/Education/ The Earth's geographic northpole is near the magnetic northpole. But if the Earth's magnetic northpole is up north, why does a compass point up north? Then the magnetic northpole has to be a magnetic southpole, because south and north attract each other. So, my question is: Why isn't the Earth's magnetic northpole a "true" magnetic northpole?

Yours sincerely Asa

Reply

Your question has come up before and it is not really about science, but about language. The needle of the compass--or of any bar magnet-- has two ends, the N end tends to point to the north magnetic pole of Earth and the S end tends to point to the south magnetic pole.

So, if the source of the Earth's magnetism were a very powerful bar magnet somewhere deep inside, where would its N pole be and where its S pole? The answer, of course, is--the S pole would be at the northern end and the N pole at the southern end. How confusing!

Teachers and students have struggled with this ambiguity since times immemorial. One popular solution has been to call the N pole of a bar magnet, not its "north pole" but its "north-seeking pole", and the other end its "south-seeking pole," marking them N and S for short. You might try doing so with your students, too.

Sincerely

David

Question #28

I am a complete novice with regard to electric and magnetic energy. Where might I find some simple introduction to magnetic and electric energy? Are human (or other living creatures) producers of electric and magnetic energy?

Reply

Dear Carolyn

Look up some physics textbook at a level you are comfortable with, section on electricity and magnetism. You will find it describes components named capacitors and inductors. A charged capacitor stores electric energy, and an inductor with current flowing through it stores magnetic energy. Break the current through the inductor, or short-circuit the capacitor and that energy can create a visible spark.

The amount of energy stored, in general, is not large, but in devices using alternating current or radio frequency, you usually only need store energy for half a cycle, a short time. Thus an inductor (the ballast coil) is sufficient to keep a fluorescent tube lit when the AC cycle goes through zero (or more accurately, relight it afterwards), and a power supply converting AC to DC (on a radio, etc.) has a capacitor to maintain the power input over such breaks, too.

The human body stores no appreciable electric energy, because it conducts electricity too well (blood is a salt solution!) to hold electric charge; an exception may exist with electric eels, I don't know how they work. Also, electrical currents in the body are tiny, so no appreciable magnetic energy is generated.

Question #29

I am a student at the American school in Karachi and have been doing research on solar wind. I have found your website to be a useful source for primary data but have one question: is there a relationship between solar wind and solar flares? I have gathered lots of data on both but they don't seem to be connected.

Reply

Is there a connection? Depends what you mean by solar flares... The solar wind originates in the solar corona, essentially because the corona is too hot to be held by gravity (and conducts heat too well). It blows all the time.

Flares are impulsive releases of magnetic energy, seen by the light they emit in the chromosphere--which is below the corona, though the place where the energy is released may be elsewhere. Flares are quite sporadic--most of the time there are no conspicuous ones. So on the face of it, no connection.

However... we do not know too well what makes the corona so hot. One theory which is getting popular (see note in latest "Scientific American"--December 2000, p. 28) is that a lot of little flare-like releases of magnetic energy occur at the base of the corona or below it. So in this sense, maybe yes, there is a connection.

Question #30

Does ozone also effect the magnetic field around the earth? I know it is also highly magnetic. What effect would the depletion of ozone, caused by pollution have on the magnetic field surrounding the Earth?

Reply

As far as I know, ozone has no effect. I am not familiar with the magnetic properties of ozone --how paramagnetic it may be--but you should realize that the total amount of ozone in the upper atmosphere is very small, less than 10 parts per million of the atmosphere above 30 km (fig 10.2, p. 157, in the chapter on ozone of "The Upper Atmosphere and Magnetosphere", Natl Acad. of Sci. 1977).

Ozone is not a recognized as a factor in any model of the Earth's distant magnetic field, whereas electric currents in the ionospheric E-layer (125 km) do play an important role there.

Question #31

David,

I really enjoyed reading the information on the site regarding the magnetosphere but I was unable to find the answer to a question I have.

What would Earth be like if there was no magnetosphere or if the strength of the magnetosphere was decreased to the point the inner radiation belt was at the Earth's surface instead of a diameter away?

Reply

Dear Jim

All these "what if" questions have been answered by nature.

If the Earth had no magnetic field of its own but an atmosphere, the solar wind would hit the top of the atmosphere, create there a standing shock and then flow around. Much like the actual magnetosphere--but the obstacle would be much smaller, and of course, no trapped particles. That's the case with the planet Venus,

If the Earth had no magnetic field AND no atmosphere, it would be like the Moon. The solar wind hits the Moon and is absorbed--but it is so rarefied that it does not make much of a difference. The interplanetary magnetic field goes through the Moon as if it weren't there, because the Moon is an electric insulator--and you know well that a magnet can pull through a sheet of paper or other insulators. Further behind the Moon is a wake of sorts, because a "shadow cylinder" there is left empty of the solar wind (that's the part lost when it hit the surface) and like the eddies behind a moving truck, the gas from the sides gradually fills that space again.

The lower limit of the inner radiation belt is set by the atmosphere. It ends gradually, where the density of air gets high enough, so that the lifetime of a trapped proton is not a year but a month, a week, a day or (if you go down further) even less. If no atmosphere existed, the protons would hit the surface SOMEWHERE--usually, where the field was weakest-- and the radiation belt would stop there. In other regions, where the field is stronger, the lower boundary would be well above the ground. In the actual magnetosphere, the weakest field is above the southern Atlantic ocean, so that's where the inner belt may come down to, say, 600 km--but after that, collisions with the atmosphere quickly put a limit to it even there.