The Van Allen Belts and Outer Space Plasmas.

 

Notes to Teachers

The following discussions make use of the following concepts and terms: Atoms, Electrons, Protons, Neutrons, Ions, Plasma, Magnetism, density, speed, gravity, force.

Based on the National Space Science Education Benchmarks (AAAS Project 2061) and most available earth and physical science textbooks used in K12 education, students have been exposed to these concepts by Grade 9. In a number of textbooks that are commonly used in Grade 5-8, terms such as density, force, magnetism, gravity and the basic structure of atoms has been introduced.

 

General education goals after reading this essay:

Critical-Response Skills

12E (6-8)-1 Be aware that there may be more than one good way to interpret a given set of findings

12E (9-12)-4 Insist that the critical assumptions behund any line of reasoning be made explicit so that the validity of the position being taken can be judged

Communication Skills

12D (9-12)-6 Participate in group discussions on scientific topics by restating or summarizing what others have said

Computation and Estimation

12B (9-12)-2 Find answers to problems by substituting values in simple equatuions

12B (9-12)-6 Express and compare very small and very large numbers

12B (6-8)-5 Estimate distances and travel times from scale drawings

12B (6-8) -3 Know that often different explanations can be given for the same evidence

Scale

11D (9-12)-1 Representing numbers as powers of ten makes it easier to compare things that differ greatly

11D (6-8)-1 As complexity increases, scientists depend on averages and summaries to describe a system

11D (3-5) -1 Almost anything has limits on how big or small it can be

 

Constancy and Change

11C (9-12) A system in equilibrim maye return to it if disturbances are not too severe

11C (9-12) Graphs and equations are useful ways to analyze patterns of change

11C (9-12) Most systems are so complex that their precise behavior is unpredictable

11C (6-8) Many systems contain feedbacks that keep the changes within specific limits

 

Introduction.

One of the most commonly asked questions about Outer Space is 'Where does the atmosphere end, and where does space actually begin?' Believe it or not, the Space Shuttle and the Space Station orbit Earth while still inside Earth's atmosphere. There is no hard edge to the atmosphere to mark where it ends and where the vacuum of space starts. Our atmosphere just gets thinner until it blends with other dilute gases in interplanetary space. Visit the NASA Glenn Research Center's 'Interactive Atmosphere Simulator' to explore how density and temperature change with altitude.

Relevant AAS Benchmark (6-8) 11B-Models are often used to think about things that cant be easily seen

(9-12) 12B-2 find answers to problems by substituting values in simple formulas

(9-12) 11B-1 Mathematical models can be used to represent physical systems

Activity 1 Use a simple equation to calculate air density at the height of the Space Shuttle

....Figure 1)

In the part of the atmosphere where the gas is dense, say at sea level, we feel currents of air caused by the motion of heated air from warmer to cooler areas. The air is heated by contact with the oceans and land, and the Sun is the main source of this heating. This motion drives a complex system of weather patterns that bring everything from a clear, sunny day to a furious thunderstorm or deadly hurricane. These weather systems are very potent in moving dust, soil, and at times rocks and houses, not because of the speed of the air, because of its density. Have someone throw a bag of sand at you. It hurts! Now have someone throw the same-sized bag but with 10 grains of sand in it. You hardly feel anything!! At sea-level, there are over a trillion trillion atoms of gas in every cubic centimeter. If you travel 100 kilometers above the ground, there are only a million atoms per cubic centimeter. As you travel even higher, to 10,000 kilometers, the density of the air drops to only 100 atoms per cubic centimeter or less. So, when astronauts work in space, they are not traveling through a vacuum at all. There is still air up there, but so little of it that even at astronaut speeds of 28,000 km/hour they hardly notice any breeze. Check out the Satellite Lifetimes Page at IPS in Australia to see how the atmosphere affects how long satellites can remain in orbit...even at 250 kilometers!

 (Relevant AAS Benchmark....(

Activity 2....Use the satellite lifetimes chart to estimate the lifetime for a satellite orbiting 1000 km which requires extrapolating a model.

Figure 2)

 

Because there is still 'air' surrounding Earth in space, are there also currents and storms up there as well just like the ones at ground level? The answer to this is 'Yes' but not the kinds of storms and currents we are so familiar with. The thing that makes them different is that the particles are charged. This lets them interact with each other and with Earth' s magnetic field in complex ways, so complex in fact that it took much of the 20th Century to discover their many motions, and what they were doing together as a system. This system is very complex because it involves the interactions between charged particles and magnetic fields.

 

States of Matter: The Mysterious Plasma State

It sounds like a mysterious word, and unless you watch a lot of science fiction programs on TV you have probably not heard this word very often. The truth of the matter is that, even though it is a rare word, in fact, all of the visible universe is in this so-called fourth state of matter beyond the familiar Solid:Liquid:Gas phases. Here's a great page at Perdue University that shows the differences between solid-liquid-gas better.

(Relevant AAS Benchmark (6-8) 4D-1 and 4D-3 about atoms and 3 phases of matter

Activity 3... Use the plasma chart to compare different terrestrial plasmas to ones found in space.

Plasma Diagram)

If you heat a gas hot enough, the atoms in it will collide so violently that molecules will be shaken apart, and the individual atoms like oxygen and nitrogen will lose one or more of their many electrons that orbit their nuclei. Every atom consists of a heavy nucleus that contains one or more protons and neutrons. This dense core is what gives an atom nearly all of its mass. Surrounding the nucleus is a cloud of electrons; one electron for every proton in the nucleus. You now have a 'neutral' atom because there are just as many negative electrons as there are positively-charged protons. If you hit this atom hard enough with another atom, energetic particle or even a particle of light (photon) you can knock one or more of the electrons out. If the atom had 8 protons and 8 electrons (oxygen for example), knocking one of the electrons out now makes 8 protons and 7 electrons. The atom now has a net charge of +1 because the 7 electrons cancil the positive charges of 7 of the protons in the nucleus, but there is one remaining proton with a positive charge. If you removed 6 electrons from the oxygen atom, it would have a positive net charge of +6. Atoms that have a net charge are called ions. So, a plasma is a gas in which some, but not necessarily all, of the atoms have been converted into ionsVisit NASA's Space Place for a great discuussion about ions. Did you know that the Deep Space 1 spacecraft used an Ion Engine to propell itself through space, just like in science fiction stories?

(Relevant AAS Benchmark. (9-12) 4D-1 and 2 'Structure of atoms. and neutrality

(9-12) 4F-4 Equal and opposite forces

(9-12) 12B-2 substitute values in simple equation

Activity 4....Throwing ions out the back of a rocket produces an equal and opposite force moving the rocket forward..

Figure 4)

Forces and Motion

Usually, plasmas are very messy because they contain mixtures of neutral atoms, ions and electrons. Each of these three components behaves differently.

The, light fast-moving electrons can produce currents of 'electricity'. These currents can produce magnetic fields just the way that a current flowing through a wire wrapped around a nail produces an electromagnet which you can use to pick up paperclips.

(Relevant AAS Banchmark (6-8) 4D-1 Electric currents and magnets produce forces

(9-12) 12B-2 substitute values in simple equation

Activity 5....calculate how current flow produces magnetic fields in simple solenoid.

Figure 5)

 

The ions are heavier and move more slowly. They can also produce magnetic fields like the electron currents, but they are much weaker because the ions move slower and so their currents are slower. Although the electrons hardly notice they are there, the ions can collide with the other neutral atoms like billiard balls on a pool table. This causes friction, and whenever you have friction, something gets hot as energy is exchanged. The electrons feel a little bit of friction with the ions, and the ions feel a lot of friction with the neutral atoms.

Benchmark (9-12) 4G-3 electrons move faster in matter and cause forces

(9-12) 12B-2 substitute values in simple equation

(6-8) 4E-1 Energy is exchanged and transformed but not destroyed

Activity. If two particles carry the same energy, the less massive particle moves faster.

Another thing that is important with plasmas is that because there are charged particles involved, they can affect each other over very large distances. Neutral atoms have to literally hit each other like billiard balls in order to affect each other. Because charged particles can attract or repell each other across a large distance, they have a much bigger reach physically. They can also generate magnetic fields and interact with magnetic fields that are already present. Amazingly, electrostatic forces are much stronger than gravity. The entire gravitational force of the Earth acting on a paperclip cannot win a tug-of-war with a simple toy magnet! I n space, when it comes to deciding what plasma will do next, it depends almost entirely on the pushes and pulls of electromagnetic forces alone. When charged particles orbit the Earth, they do not follow paths like the Space Shuttle that is controlled by gravity. The orbits of plasmas are complex paths often determined by the Earth's magnetic field and how charged particles interact with it.

(Relevant AAS Benchmark (9-12) 4G-1 electrostatic forces are stronger than gravity

(9-12) 12B-2 substitute values in simple equation

Activity 6....Compare electrostatic, magnetic and gravitational attractions quantitatively

Figure 6)

 

 

Solar Influences.

Another important influence on the Earth is solar radiation. At ground level, this radiation is mostly benign but you still need some protection from it by using a skin ointment or 'Sunblock'. Solar radiation spans a vast spectrum of energies called the Electromagnetic Spectrum, that extends from very short wavelengths of light called X-rays, through visible light which our eye sees, and on to longer wavelengths in the infrared and radio portions. A rule of thumb is that the shorter the wavelength, the more energy that is carried by the light. This is why ultraviolet light (the short wave part of the visible spectrum) is much more harmful than infrared light. The chemistry of living systems, called organic chemistry, requires energies typical of the light in the visible spectrum in order to 'power' the many complex pathways that lead to living systems and their metabolism. Too much of a good thing, however, causes cellular damage, not just at the outer surface of a cell, but genetic damage deep inside the cell's nucleus.

(Relevant AAS Benchmark....(9-12) 4F-3. Accelerating electric charges produce light.

(9-12) 4F-5. Electromagnetic waves and spectrum

(9-12) 12B-2 substitute values in simple equation

Activity 7....Compare energy carried by EM radiation at different wavelengths.

Figure 7)

Luckily, or perhaps inevitably, a planet like Earth with an oxygen atmosphere has a way of shielding the ground from much of this harmful radiation. At 20 km, oxygen atoms become rearranged into a molecule called ozone which then absorbs most of the solar ultraviolet radiation at short wavelengths. Without the ozone layer, life on the land would be impossible because of the tremendous genetic damage and mutation that would occur. Infact, until oxygen respiring bacteria managed to increase the oxygen in Earth atmosphere 560 million years ago, Earth's surface was sterile and life could only exist in the oceans. It took over 3 billion years for this critical transformation to happen!

(Relevant AAS Benchmark....

Activity 8....Figure 8)

At even higher altitudes, however, the atmosphere is so thin that solar radiation is hardly blocked at all. Nearly all of the wavelengths in the electromagnetic spectrum are available to deliver energy to anything that is absorbs them. Individual molecules of nitrogen (N2), oxygen (O2) and water (H2O) are 'zapped' by solar ultraviolet light and become ionized into N+, O+ and H+. Do you know another name for a hydrogen ion? So, as we move higher up in the atmosphere, the atmosphere thins out, but because it is also less able to shield itself from solar radiation, it also becomes a plasma. This changes everything. The motions for neutral atoms that we were so familiar with near the ground now change into the more complex motions of ionic plasmas.

To understand how these plasmas move, and where they are located, we have to realize that they are almost completly under the control of Earth's magnetic field. Gravity has virtually nothing to do with how they move or behave. The region of space surrounding the Earth where its own magnetic forces are important in controlling plasma is called the Magnetosphere.

 

The Magnetosphere

You have probably seen the experiement where a bar magnet is placed under a piece of paper, and iron filings are spirinkled on top. Beautiful curved lines begin to form that follow the magnetic field 'lines' of the magnet. The lines spread out and become weaker the farther from the magnet you get, but they also get stronger near the ends of the magnet in the areas called the poles. Every magnet has exactly two poles which we have historically called 'North' and 'South'. Like charged particles, opposite 'poles' attract and like 'poles' repell.

(Relevant AAS Benchmark....(3-5) 4G-2 magnets cause pulls and pushes.

(9-12) 12B-2 substitute values in simple equation

Activity 9....(9-12) Calculate a magnetic dipole pattern using a simple trig equation for a field line.

Figure 9)

The Earth's field is not like a toy magnet field at all, because it isn't a 'permanent' magnet. It is more like the electromagnet that you make when you let a current flow through a wire wrapped around a nail. If you take away the current, the magnetism dissappears. Deep inside the Earth, just outside its core, there is a very hot liquid region of iron and nickle which flows like a great river along the equatorial regions. This liquid is electrically active and forms an electrical current. It is the flow of this current that generates Earth's main field. The field penetrates through the entire solid Earth, though it is affected here and there by deep deposits of iron ore beneith the crust.

(Relevant AAS Benchmark....(6-8) 4C-1 Interior of the earth is hot

(6-8) 4G-magnetic effects of currents.

(9-12) 4C-3 'slow movement of material inside earth

(9-12) 4G-5 moving elecric charges produce magnetism

(9-12) 12B-2 substitute values in simple equation

Activity 10....Calculate the current in the earths core from its magnetic field strength

Figure 10)

As it leaves the lithosphere which carries the continents and oceans, it continues to expand and weaken. It still looks almost identical to a toy bar magnet field, but at its outer limits 60,000 miles from the surface, it changes in a number of dramatic ways. This happens because, as it steadily weakens in strength, other currents from charged particles flowing around the earth, creats their own magnetic fields that interact with Earth's. Even the solar wind streaming by, distorts Earth's magnetic field into a comet-like shape. The region of space where Earth's field is more important in controlling charged particles is the Magnetosphere. Just outside this zone is a thinner region called the magnetopause where solar wind pressure and Earth's magnetic pressure nearly balance each other. There is a lot of activity within the magnetosphere, and many complicated systems of particles that exchange energy with each other.

(Relevant AAS Benchmark....(6-8) 4B-3 'Everything near earth is pulled by gravity

Activity 11....From a scaled diagram, determine the distances to different regions TBD

Figure 11)

 

 

Bouncing Plasmas.

To understand what these different plasma systems are doing, you have to first understand how they are moving. When the Space Shuttle orbits Earth, its path is a nearly circular path with a center at the core of the Earth. Gravity is the only force that is of any significant consequence in determining this path given the amount of energy (e.g. speed) of the Space Shuttle. The motion of particles in magnetic fields can be more complicated. The best way to think of plasma motion is to imagine yourelf an individual charged particle. The basic rule of thumb is that you orbit whichever magnetic field line happens to be in your vicinity. You can also move along this magnetic field line at the same time, so your path looks like a coiled spring that is bent along the shape of a magnetic field line.

(Relevant AAS Benchmark....(6-8) 4G-3 electric currents and magnets exert forces on each other

(9-12) 12B-2 substitute values in simple equation

Activity 12....Compute the velocity vector of an electron on a magnetic field line TBD

Figure 12)

There is a relationship between how much energy you have as a particle and the size of this orbit. Particles that carry a lot of energy have much larger orbits than particles that carry very little energy. This also means that if you are looking for small things like clouds of plasma floating around the earth, you are mostly out of luck. The typical particle energies are so high that the smallest clumps of plasma are often hundreds, and even thousands of kilometers across. This explains the first difference between the 'weather' in space and the kinds of weather systems we see here near ground level.

(Relevant AAS Benchmark....(6-8) 11B-1 Models are often used to think about processes that cant be observed directly.

(9-12) 12B-2 substitute values in simple equation

Activity 13....Calculate cyclotron frequency and radius vs energy in a table

Figure 13)

Another thing that makes the motion of space plasmas different from ordinary gas is that, because the strength of the magnetic field increases towards each pole, the orbits of the particles around the field lines becomes smaller and smaller. Then, another thing happens because energy and momentum have to be conserved. As the spiriling particles get closer to the poles in ever-tightening orbits, their forward motion along the line slows to a stop, and their direction reverses. The particle has bounced, and is now headed back out into space, unless of course it had the misfortune to collide with an oxygen or nitrogen atom in the atmosphere and become neutralized!

 

There is another kind of motion that can happen at the same time. Not only does the magnetically 'trapped' particle bounce from pole to pole 50 times an hour, but it slowly drifts in an eastern or western direction around Earth. Although this equatorial drift looks something like the orbit of the Space Shuttle, in fact it has nothing to do with gravity at all. To make thinks even more bizzare, particles with positive charges will drift westward while at the same time, particles with a negative charge will drift eastwards! Because the density of the plasma is so low, individual particles hardly collide with each other, and so you can have two plasmas flowing in opposite directions in the same volume of space! This is an important thing to keep in mind, because in the next section we will explore the major systems of plasmas, and many of them occupy the same volume of space around Earth. The first major space plasma system is called the ionosphere. It's the easiest one to picture in your mind's eye, and the first one discovered.

(Relevant AAS Benchmark....

(9-12) 12B-2 substitute values in simple equation

Activity 14....Particle collision times in gases of various densities

Figure 14 coexisting particle systems)

 

 

The Ionosphere.

In 1905, G. Marcconi invented the first radio transmitter, but his transatlantic message to America raised an important scientific puzzle. What was causing the signals to 'bounce' over the horizon from England to America. The English physicist Heaviside proposed that there had to be an electrically active layer in the atmosphere about 10-50 km above the ground that reflected the radio waves before they sped aeway from Earth into the depths of space. Within a few years, the 'Kennely-Heaviside Layer' was renamed the Ionosphere in honor of the fact that its was an atmospheric layer consisting of a mix of ions and electrons. Typically about 1000 electrons per cubic centimeter during the daytime, but still thousands of times more than what you would ever find at sea level.

The ionosphere has been extensively studied by scientists and countless numbers of 'Ham' radio operators. Scientists often describe something, the first time they discover it, as being more or less featureless. These initial simple models help them understand the rough properties of a new unfamiliar system, and are a very important first stem in moving towards a deeper understanding. We know that the ionosphere is far from being a smooth layer of ions. It is clumpy, which causes the 'twinkling' of radio signals that pass through it. There are powerful currents of electricity that flow through it. There are convection currents that connect the motions of particles at this layer, with what is happening out in space and down in the deeper layers of the atmosphere.

Benchmark....(6-8) 11A-3 Any system is usually connected to other systems

(9-12) 12B-2 substitute values in simple equation

Activity...calculate critical frequency and define electron density/reflection

We know that it is, also, a layer that can be directly affected by solar X-rays, especially during solar flares, which can cause radio backouts covering the entire sun-facing hemisphere of Earth. Solar ultraviolet and X-rays also interact with the ions of oxygen and nitrogen in the ionosphere, heating them to make them move faster. Like mineature rockets receiving added fuel, these ions steadily move higher and higher in the ionosphere, eventually leaving it. This causes a steady expansion of the atmosphere into space which has been going on for billions of years. During major solar storms, these ions are even expelled in powerful, though invisible, fountains of matter out of the polar regions.

(Relevant AAS Benchmark....(6-8) 4E-1 Energy is transformed from one form to another

Activity 15....

Figure 15)

 

The Plasmasphere

As the energies of the plasma ions increase, the plasma motions eventually become the bouncing-drifting type. Over time, the particles settle into a system called the plasmasphere. It is an invisible, donut-shaped zone barely distinct from the upper atmosphere, where low-energy particles trapped on particular magnetic field lines bounce and drift around Earth. This continues until some space storm strips them of their lines of magnetism, but there are always more ionosphere ions ready to fill these field lines back up again when the storm passes. It takes about a day or so for the plasmasphere to heal itself after a solar storm.

The plasmasphere can be detected in satellite images such as those provided by IMAGE, out to a distance of about 3 times the Earth's radius ( 3Re or 21,000 km) from Earth. Although the innermost edge seems permanent, its outer edges come and go with solar storms as its contents are shed and refilled from day to day. At a distance of about .... Re, we encounter a boundary to the plasmasphere called the plasmapause. Here, and interior to it, plasma trapped on magnetic field lines is forced to rotate exactly in step with the Earth as its magnetic field sweeps 360 degrees every 24 hours. No spacecraft controlled by gravity alone could ever keep up with this motion...(check this)

(Relevant AAS Benchmark....

 

Activity 16....Scale drawing of magnetosphere/plasmasphere....

Figure 16)

 

At the outer edge of the plasmasphere, and in some sense actually defining its boundary, we encounter the next major plasma system: The Ring Current.

 

The Ring Current.

Most of the time, it is not there at all. In a special slot between 2Re and 6Re, conditions seem to be just right that whenever a severe solar storm impacts the magnetosphere, particles appear 'out of nowhere' to fill this region with very energetic particles. One big clue about where they come from has to do with satellite measurements of the kinds of particles found there during a storm. They are mostly oxygen ions! The only nearby source of oxygen ions is Earth itself. How do they get there?

When we discussed the ionosphere and the plasmasphere, we noted that under certain stormy conditions a fountain of oxygen and nitrogen ions can be launched from the polar regions into space. Scientists think that this is where the Ring Current particles come from, but we still are not sure how it is that low-energy ions from the atmosphere can get boosted by over 1000 times in energy to become part of the ring current. There is some evidence that the origin of this energy comes from processes that are going on even farther from the Earth that heat the Ring Current plasma to high energies.

The ring current is seldom seen unless a major solar storm has just impacted the magnetosphere. Immediately after the storm begins, the ring current brightens and begins to flow around the Earth from the nighttime side to the daytime side. Along the way, its inner edge invisibly rubs against the outer regions of the plasmasphere. Plasmasphere ions pick up energy and are convected with the ring current flow to mingle their matter with this current. The ring current produces its own magnetic field, which interacts with Earths field over the equatorial regions. A significant reduction in the magnetic field at the surface of Earth often accompanies the formation of the ring current. As the storm slackens, the ring current ions rapidly diminish in numbers, perhaps because of collisions with the slower moving plasmasphere particles, and as mysteriously as it appeared, it vanishes. IMAGE satellite observations can watch the entire evolution of this system of plasma, and this has revealed many exciting new clues about how the Ring Current is produced, but there is still much more to learn!

(Relevant AAS Benchmark....

Activity 17.... The Dst index and its correlations.

Figure 17)

 

The last, major plasma system is paradoxically the best know but least understood. It also poses the greatest hazard for astronauts and satellite technology: The Van Allen Belts.

 

The Van Allen Belts.

In ..., TBD proposed that charged particles near Earth should following bouncing-drifting orbits, but it wasn't until 1958 that the tiny Explorer I satellite with its ordinary Geiger counter proved that this was in fact so. James Van Allen's experiment detected these 'trapped' particles, but there was something very odd about them. Their energies were staggering. Even today, space physicists don't fully understand where they come from or how their energies can be so 'astronomical' compared to either the plasmasphere particles or Ring Current particles. Typical 'Belt' particles consist of electrons and protons, with energies between 1 and 100 million volts. Energetic ring current particles, by comparison, hardly carry more than 150,000 volts of energy.

Most textbooks, even those that are used to train professional space physicists, show the 'Belts' as nested, donut-shaped clouds. As we saw in our section on plasma motion, particles tend to bounce from pole to pole and drift east or west. The van Allen Belt particles do likewise. Instead of smooth donuts, it would be more correct to show the clouds as having sharp poleward 'horns' rather than a smoothed shape. At the peak of the horns, particles either collide with the atmosphere and are lost from the Belts, or are reflected back into space along the magnetic field. There is also another aspect to these Belts of particular interest to manned space flight and satellites. Because the magnetic field of Earth is shifted off the rotation axis, in space, its influence is stronger in equatorial regions over South America. This also means that, because the Belts follow the Earth's magnetic field not its geographic shape, they are closer to the ground over South America and the South Atlantic.

This means that if you were in a Space Shuttle, Space Station or operating a satellite as it passes over the South Atlantic, you will be closer to the Belts and receive a larger than average dose of radiation from them as their particles penetrate your spacecraft or satellite skin. This region is called the South Atlantic Anomaly. It affects astronaut radiation dosages as well as data and signal transmission quality from all spacecraft passing through this continent-sized region.

(Relevant AAS Benchmark....(9-12) 5B-5 Gene mutations can be caused by radiation

Activity 18....Figure 18)

 

Extensive satellite studies have identified two families of particles making up the Belts. These are electrons and protons. There are two electron belts and one proton belt. The origins and energies of these belts are very different.

The proton belt is located from about 500 kilometers above Earth's surface and extends to 2RE (13,000 km) and contains hydrogen ions with energies greater then 10 million volts. These ions are inside the Ring Current zone so it is not thought that they originate from terrestrial particles. Scientists currently think that these protons are trapped cosmic ray particles from outside the solar system, or from the Sun itself possibly during severe solar flares.

The two electron belts are segregated into a high-energy belt and a low-energy belt. The low-energy belt is

(Relevant AAS Benchmark....Activity 19....Figure 19)

 

Humans have been affected by Belt particles, though not as severly as some people might believe. Space Shuttle and Space Station astronauts inside their crafts receive about 2? mRems of additional dosage each time they pass through the SAA. Over the course of a week, this adds up to 7 x 30 = 210 mRems which is just below the dosage you get at ground-level in a single year (about 350mRem). Apollo astronauts, however, were forced to traverse the most intense regions of the Belts in their journey to the Moon. Fortunately, the travel time was only about 30 minutes so their exposures were not much more than the total dose received by Space Shuttle astronauts (TBD). This fact counters some modern speculations that the moonlandings were a hoax because astronauts would have instantly died as they made the travel through the belts. They may have experienced minor radiation poisoning if they had been in their spacesuits on a spacewalk, but no spacewalk was ever scheduled for these very reasons. The shielding provided by the Apollo space capsule walls was more than enough to shield the astronauts from all but the most energetic, and rare, particles. Still, the astronauts reported seeing 'shooting stars' (TBD?). These were caused by very energetic particles streaking through the fluid in the eye and leaving behind a luminous, but fleeting, trail of light. Similar streaks have ben reported by astronauts in the Space Shuttle and other near-earth missions during solar storms. It is not known what the long-term consequences of these kinds of brief exposures are upon astronauts, but prospective travelers to Mars will no doubt see many more of them!

(Relevant AAS Benchmark....

Activity 20....Use a graph to estimate radiation exposure to astronauts vs sheilding

Figure 20)

Humans have also made a significant impact upon the Belts through older programs of nuclear testing. In fact, during tests in ...., humans temporarily created a new belt in a 'notch' region just beyond the proton belt. This temporary belt eventually dissipated, but its traces could still be detected in ca 1980's. (Relevant AAS Banchmark....Activity 21....Figure 21)

 

Reading to be Informed Questions

Because of the level of detail, this activity is only recommended for Grade 9-12.

1) Where do scientists think that the Ring Current particles originate? Why?

2) Do the items mentioned in the essay constitute a system?

3) What are the major exchanges of matter and energy that are descibed within the magnetosphere?

4) How do scientists study the Ring Current from the ground?

5) Why is it difficult to study space plasmas?

6) Explain how a radar gun could be used to study invisible clouds of plasma?

7) Why does the ionosphere reflect radio waves? Under what specific conditions would it reflect radio waves with a frequency of 1 gigaHertz?

8) How are the plasmasphere and ionosphere related to each other?

9) Why do scientists have such a hard time understanding the origin of the van Allen Belts?

10) What is the process called 'magnetic reconnection' and why is it important in space physics?

11) What is at least one aspect of space plasmas near earth that scientists currently can not explain?

12) How do scientists develop explanations for processes operating in space?

13) How do terrestrial experiments help scientists construct better models for the magnetosphere?

14) How do charged particles move in magnetic fields in space?

15) Why do positive charges circulate westward and negative charges eastward?

16) Why dont particles traveling in opposite directions collide and disrupt the flows?

17) Are the van allen belts a danger to astronauts?

 

 

More Good Stuff!

For more information about this material, consider visiting the following websites: 

  1. Exploration of the Earth's Magnetosphere' at GSFC by Dr. David Stern.
  2. At SPENVIS.OMA.BE
  3. ssdoo/Education
  4. JPL/Basics
  5. NASA/HQ/PAO
  6. NASA/HQ/PAO
  7. NASA/HQ/BROWSE
  8. POETRY/Storm22
  9. ISTP
  10. OULU/textbook
  11. www.encyclopedia
  12. commkey
  13. clavius.org/envrad
  14. clavius.org/envrad2
  15. Science Forum
  16. GSFC
  17. albany.edu
  18. JSC
  19. globalpolicy.org
  20. GSFC
  21. spacedaily
  22. ScienceNet
  23. Spaceviews
  24. Ulysses
  25. Voyagetothebottom
  26. AGU
  27. NASA
  28. ESTEC
  29. JSC

QUESTIONS and ANSWERS:

  1. What are they? (Imagine the Universe FAQ
  2. Can organic matter pass through them?
  3. What is the South Atlantic Anomaly?
  4. Can astronauts travel throuigh them safly?

 

Illustrations:

 

From David Stern 'Exploration of the Magnetosphere' Mirroring particles from David Stern.

Drifting particles by David Stern.

Trapped particles. from SPENVIS.

 

Trapped proton belt. From AP-8 MAX (SPENVIS)

 

Trapped electron belt. From AE-8 MAX (SPENVIS)

South Atlantic Anomaly. From AP-8 MAX (SPENVIS)

SAA and electron distribution. From AE-8 MAX (SPENVIS)

Trapped particle motions. From http://www.estec.esa.nl/wmwww/wma/rad_env.html

SAA. From http://www.estec.esa.nl/wmwww/wma/rad_env.html

SAA close up in orbit. From http://www.estec.esa.nl/wmwww/wma/rad_env.html

SAA at surface. Intensity map. From http://www.estec.esa.nl/wmwww/wma/rad_env.html

 

 

(Picture 1. See Credits below)

(Picture 2. See Credits below)

Radiation belts. Van Allen's picture of the inner and outer zones of the radiation belt made after Pioneer 3 data returns. J. A. Van Allen and L. A. Frank, from Nature 183 (1959). 430; copyright Macmillan Journals Ltd., 1959. (Picture 3. See Credits below)

It once was thought that the Earth was surrounded by near-empty space, in which the Earth's magneticfield would trace a pattern resembling that of a bar magnet (orange lines). However, the first American spacecraft, Explorer 1 (shown here), discovered a belt of energetic particles trapped in thefield and streaming back and forth above the Earth. It was the first of two such zones, the Van Allen belts, to be found. (Picture 4. See Credits below)

Simulated Van Allen Belts generated by plasma thruster in tank #5 Electric Propulsion Laboratory at the Lewis Research Center, Cleveland Ohio, now John H. Glenn Research Center at Lewis Field. (Picture 5. See Credits below)

(Picture 6atozscience )

http://www.spacedaily.com/news/earth-magnetic-99d.html

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