RANDY L. PHELPS

This is the Magnetospheres Module

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Procedure

1.  For this module, please look through the "lecture" notes for "Planetary Magnetospheres".  These notes contain the material, in condensed form, that I will expect you to become familiar with.  I am sure you will have questions about the material, especially since it is presented in the form of lecture notes.  To help you fill in the blanks, I have added web links that you can follow, in order to gain further insight into the material. 

2.  Seemingly, a large fraction of the class is unfamiliar with the demonstration of dropping iron filings around a bar magnet.   There are a couple of web-based demonstrations, outlined below, that you should do to help you understand the material, and reinforce the concepts:

Web-Exercise 1: Bar Magnets  This is a simple demonstration showing what happens when you place a bar magnetic among flakes of iron (iron filings).  When you first visit the site, you will notice that the orientation of the iron filings is random.  To simulate what happens when you place a bar magnet among the filings, simply turn "on" the magnet by clicking on the "on" button. below the image.  Notice the pattern of the iron filings.  The filings trace the direction of the magnetic field lines.

Web-Exercise 2: The Earth's Magnetic Field In this interactive demonstration, you are asked to click around the Earth with your mouse button to in essence place iron filings around the Earth (consider these to be high-tech sensors, launched by NASA, that detect magnetic fields - it sounds better than saying they are iron filings!).  Place a large number of them there by clicking frequently all around the Earth.  If you place enough of them, you will begin to notice a pattern that shows what the magnetic field of the Earth looks like.   Additionally, you can move the Earth through the filings (or around your detectors!), by positioning your mouse button over the Earth, holding the button down, and then moving the Earth around the screen (through space!).  Notice how the space around Earth reacts to the Earth's magnetic field.  NOTE:   This demonstration had problems at the source on 10/12/2000.

Upon completing this assignment, you should be comfortable with the following material:

• Definitions and Concepts:  Magnetic regions around planets (magnetosphere, magnetopause, magnetosheath, bow shock, magnetotail, plasma sheet).
• Aurorae, and what causes them.
• Characteristics of the magnetic fields of various Solar System objects.
• How to predict the presence of magnetic fields around planets and moons.

Upon completing this assignment, you should be able to answer these, and similar questions

General Concepts

• What is a magnetosphere?  What is a bow shock?  What is a magnetosheath?  What is a magnetopause?  What is a magnetotail?  What is a plasma sheet? 
• Why do aurorae occur in the polar regions of the Earth?
• Why are different colors seen in aurorae?
• What can one say about a planet's interior if aurorae are seen in its atmosphere?
• Which planets in the Solar System have obvious magnetospheres?
• Are the magnetic fields of the outer planets stronger or weaker than those in the inner Solar System?
• Have magnetic field been detected around planetary satellites/moons?
• What are the unusual characteristics of the magnetic fields of Uranus and Neptune?

Applications

• A planet has a rotation period of 10 hours, and a strong magnetic field.   What can be said about its interior?
• A planet has a rotation period of 100 days, and no magnetic field is detected.  What can be said about its interior?
• A planet has a magnetic field, whose axis is tipped 90 degrees relative to its rotation axis.  Where would one expect to observe aurorae on this strange planet?
• The moon does not have a significant magnetic field, and its rotation period is about 27 days.  What can be said about its interior from this information?
• Venus does not have a significant magnetic field, and its rotation period is about 243 days.  What can be said about its interior from this information?
• Mercury has a rotation period of 59 days.  Would you expect to observe a strong magnetic field?
• Mars has a rotation period of 24.6 hours.  If Mars had a fluid interior, would you expect to observe a magnetic field?
• Jupiter has a rotation period of 10 hours, and it has an enormous magnetic field.  What can be said about its interior from this information?
• Would one expect a strong magnetic field around Pluto?

These questions, and similar ones, will form the basis of  the exam material for this section of the course.  If you have problems with the material, please see me.   If you are unable to answer some of the questions, I will help you before the date specified on the syllabus, provided you show me the results of your inquiry into the material.

That is, you must provide me the answers you we able to obtain for all questions, including your attempts at problem questions, before I will help you with any of them!   

In other words, for me to provide you with help with the questions, you must show me that you have undertaken a good-faith-effort to find the answers yourself, in a timely manner.

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