Planet Earth: a great magnet

  An artists conception of the Earth's magnetosphere. Courtesy of the Space Science Institute. Artwork by Steve Mercer.
Our planet is a giant magnet. You prove this each time you use a compass, but beyond that probably don't notice it much. You may not think of magnetism at all while viewing an aurora, the beautiful light show of polar skies. Or when your AM radio won't tune in, or when your power won't turn on. But all these things are affected by Earth's magnetic field.

Earth's invisible magnetic field extends far out into space to form a region we call the magnetosphere. The force of the solar wind pushes on the magnetosphere, squeezing in the Sunward side and stretching the night side into a long tail (called the magetotail) that extends hundreds of thousands of miles into space. As the solar wind flows past the magnetosphere, it acts like a cosmic generator, producing millions of amps of electric current. Some of this electric current flows into Earth's upper atmosphere which can light up like a neon tube to create the mysterious aurora (Northern and Southern Lights).

A diagram of the Earth's magnetic field, which near the Earth resembles that of a bar magnet. Courtesy NASA.
There are many unique regions in and near Earth's magnetosphere: the bow shock, magnetotail, radiation belts, and the ionosphere. Earth's magnetic field acts like a shield to the supersonic solar wind. A shock wave (called the bow shock), like that produced by supersonic aircraft, slows and heats the solar wind. The magnetotail extends far away from Earth on the nightside. It is in the magnetotail, that charged particles are energized and directed toward the polar regions where they cause the aurora.

The First Major Discovery of the Space Age

The Van Allen Radiation Belts were discovered by Explorers 1 and 3 in 1958. More...
Over 98% of the charged particles from the Sun and from galactic cosmic rays that strike Earth's magnetosphere are deflected by it! The Van Allen Radiation Belts -- two doughnut shaped belts that surround the Earth -- trap the rest of the harmful particles, which bounce back and forth along magnetic field lines between Earth's north and south magnetic poles like beads on a wire.

In the upper part of Earth's atmosphere, right at the edge of Electric Space, lies a charged layer of plasma and neutral gases called the ionosphere. It extends from 50 to 300 miles above the surface of Earth. Here, ultraviolet rays from the Sun and high-energy particles from outer space bombard the gases of our atmosphere. They collide with the atoms, knocking off electrons and leaving the positively charged nucleii--called ions--floating free. Because of these free-floating charged particles, the ionosphere can conduct electricity. During disturbed conditions, huge currents can flow which cause Earth's most spectacular light show: the aurora.


Earth's magnetosphere is very sensitive to space weather. During the Sun's most active periods, solar wind disturbances, created by coronal mass ejections and flares, buffet Earth's magnetosphere and they can produce large magnetic storms lasting one or more days. Magnetic storms have been known to seriously damage electric power networks, affect communications, and damage satellites orbiting near Earth.