MadSci Network: Astronomy
Query:

Re: what is the interaction between cosmic radiation and Earth's magnetic field

Area: Astronomy
Posted By: Jay H. Hartley, Grad Student,Lawrence Livermore National Lab
Date: Tue Feb 11 12:16:24 1997
Message:

Well, Phillip, you have a very interesting theory. First I'll address your initial question about cosmic radiation and the Earth's magnetic field, then we'll get back to your idea for heating the core.

When astronomers discuss "cosmic radiation," or more commonly "cosmic rays," they refer to electrically charged particles coming from sources outside of our solar system. The particles can have very high energy, even beyond what we can produce in our most powerful accelerators. Their exact source is a mystery, and they are an interesting topic all on their own.

In your question, you are talking about what astronomers call the "solar wind." This is a stream of charged particles that are constantly being ejected from the violent surface of the sun. They are at much lower energy than cosmic rays, but still travelling up to 1 million miles per hour, and there are many more of them. I say "many," but there are really only about 5 particles in a cubic centimeter, which is a much better vacuum than I can produce with the best equipment in my lab!

This current of particles is enough to distort the magnetic field of the earth. To see a picture of this distortion, check out http://wwwssl.msfc.nasa.gov:80/SSL/PAD/SPPB/edu/magnetosphere/mag2.html. When the Sun erupts with a particularly large solar flare, the added burst of particles can cause variations in the Earth's field. Such flares also distort radio transmission, can disrupt and even damage the electronics in satellites, and pose a health risk for astronauts in orbit. For this reason, scientists study the "weather" of the sun almost as closely as they do the weather here on earth, in the hopes of being able to predict these solar storms.

When a charged particle encounters a magnetic field, it is forced to travel along the field lines. In this way, the particles streaming at the earth are directed around it by the magnetic field. They follow the field lines to either the North or South pole. There they channel down into the atmosphere, and can collide with the molecules of air. This causes the oxygen and nitrogen in the air to give off light, producing the Aurorae. ("Borealis" around the north pole, "Australis" in the south.)

Some of these particles get trapped in the earth's field, travelling back and forth along the field lines from the North Pole to the South Pole. There are two large clouds of these trapped particles around the earth, shaped like big donuts. These are referred to as the Van Allen Belts. Most books you read will tell you that the Van Allen Belt particles are all from the Sun, but recent research suggests that many of the particles may come from our own atmosphere. You can learn more about a new experiment to study this question and others about the earth's "magnetosphere."

Now to your theory about the heating of the earth's core. It is true that forcing changes in a magnetic field can act back on the magnet itself and cause heating; however, I don't think there is nearly enough energy in the solar wind, even including flares, to significantly heat up the earth's core. The current in the solar wind channels about 100 million kilowatts of power into our atmosphere. That sounds like a huge amount, but the light from the sun hitting the earth delivers about 100 Watts per square meter of the earth's surface, which works out to 100,000 times the power in the solar wind (according to my quick calculations).

It is *possible*, but not certain, that solar activity might have a significant influence on our weather. An unusually quiet period of solar activity between 1645 and 1715 does correspond with a "Little Ice Age" in Europe, and a drought in colonial America, but there are many other things, such as volcano activity and such, that could also account for the climate changes.

As you can see, the interactions between the Sun and Earth are a rich, rich field of active study! I hope this gives you a taste of what is involved, and hope I didn't overwhelm you!

Stay curious,
Jay H. Hartley


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